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Early to rise makes a plant healthy, wealthy, and wise
Ecology
Abstract
Seedling emergence time is a crucial event in the life cycle of a plant, determining its fitness via different components including survival, growth, and fecundity. Precocious emergents usually survive, grow, and/or reproduce earlier in the life cycle, but for perennials it is unknown whether these benefits are maintained throughout the life of the plant. Here, we examine for the first time whether fitness benefits due to the early emergence of perennial plants are perpetuated or vanish with time. For nine years, in a Mediterranean gorse community, we followed the fate of 2118 seedlings belonging to the four dominant woody species. We estimated phenotypic selection gradients on emergence time for three fitness components (survival, growth, and fecundity), under two experimentally simulated scenarios (fire and fire þ erosion), at two different times in the life of the plant (3 and 9 years). Fire and erosion represent two potential selective forces constraining the temporal window of seedling emergence in Mediterranean habitats. All the species exhibited selection for early emergence, but through different fitness components. Directional selection favoring early emergence via survival in both fire scenarios was detected in the two Cistaceae species (Helianthemum marifolium and Cistus albidus), in which precocious emergents had higher fitness values late in the life cycle (9 years). In contrast, Fabaceae species (Ononis fruticosa and Ulex parviflorus) were not selected for early emergence via survival. Early emergents of all species in both fire scenarios had higher fitness values through growth early in the life cycle; these benefits decreased slightly with time but remained statistically significant, except in H. marifolium. Finally, late fecundity was enhanced by early emergence in both fire scenarios in C. albidus and U. parviflorus but not in H. marifolium. In conclusion, benefits acquired by emerging early are perpetuated for at least nine years.
... The timing of germination is an important factor that can affect future plant performance in terms of survival, growth, and/or fecundity [24]. Early germination can increase plant fitness in general, and the benefits can be especially pronounced in perennials, such as C. reticulata, as opposed to annuals [25,26]. Because many perennials are iteroparous and can reproduce across multiple years, their seeds tend to germinate under the best conditions that a given year offers, whereas annuals, which can only reproduce in the year in which they germinate, tend to spread germination out over time to reduce the risks associated with reproducing in only one year [25]. ...
... Early germinators reduce the time of exposure to seed predation [27]. Once seedlings germinate, early-season growing conditions may offer more abundant water and soil nutrients [28], provide better light environments in deciduous forests [29], cooler temperatures with reduced loads of pathogens and herbivores [29], offer reduced competition with siblings [8,22,25,26], and allow for more time for root establishment before the water stress of summer [21,26,[30][31][32]. In the Wasatch Mountains, establishment before summer drought is particularly key. ...
... Early germinators reduce the time of exposure to seed predation [27]. Once seedlings germinate, early-season growing conditions may offer more abundant water and soil nutrients [28], provide better light environments in deciduous forests [29], cooler temperatures with reduced loads of pathogens and herbivores [29], offer reduced competition with siblings [8,22,25,26], and allow for more time for root establishment before the water stress of summer [21,26,[30][31][32]. In the Wasatch Mountains, establishment before summer drought is particularly key. ...
Research Highlights: Frugivory by mammals is a common plant–animal interaction, but additional studies that examine the effects of frugivory on woody plants are needed. We show that ingestion of netleaf hackberry (Celtis reticulata Torr.) fruits by coyotes (Canis latrans Say) cuts the time to germination nearly in half and results in seedlings that are taller than the controls. Background and Objectives: Netleaf hackberry is a deciduous shrub to small tree that can be long-lived, but newly established stands are rare. The lack of juvenile hackberry in its native range of southwestern North America could be due to low percentages of germination and seedling survival. We hypothesized that passage through the digestive tract of a coyote would increase the germination and subsequent growth of netleaf hackberry. Materials and Methods: In the Wasatch Mountains of Utah, we collected coyote scats containing visible hackberry fruits and picked fresh fruits from nearby hackberry shrubs. All samples were cleaned and cold-stratified. We sowed 20 seeds from each of the 34 samples into containers in the greenhouse (a total of 680 seeds). We noted the date of emergence and final height of each seedling after 131 days. Results: The germination percentage of the coyote-treatment seeds did not differ from that of the controls. However, the coyote-ingested seeds took just over half as many days to germinate as did the undigested controls (35 days vs. 69 days, respectively; p < 0.001) and the resulting seedlings were 9.5% taller by the end of the growing season (6.4 vs. 5.8 cm, respectively; p < 0.001). Conclusions: Consumption by coyotes can benefit hackberries by enabling their seeds to germinate earlier in the year when conditions are wetter and cooler. The additional time for establishment and growth afforded by frugivory likely increases the fitness of netleaf hackberry seedlings that emerge into the unpredictable conditions of a semi-arid region.
... Perennial plant species do not need to spread the emergence risk temporally because they are more independent of temporal environmental variation than annuals, due to their iteroparous reproduction (Rees, 1996). However, in perennials, early emergence is often related to higher fitness and fecundity in terms of seedling recruitment, survival, height, biomass and number of flowers (Cook, 1980;Verdú and Traveset, 2005;De Luis et al., 2008). Germination differences of 15 d have even been detectable 3 years later in the perennial Viola blanda (Cook, 1980). ...
... Especially for autumn-germinated seedlings of perennials or winter annuals, which have to survive the unfavourable winter period, larger and thus more vigorous seedlings have an advantage (Leishman et al., 2000;Schmiede et al., 2013). Similarly, seedling emergence early in spring is advantageous when competing with crops (Black and Wilkinson, 1963;Dyer et al., 2000;De Luis et al., 2008). On the other hand, these seedlings are especially threatened by environmental hazards, such as spring drought or frost and agricultural measurements (Jones and Sharitz, 1989;Storkey et al., 2010). ...
... This is in line with a former study about the impact of seedling emergence time of subterranean clover, where a germination delay of 5 d led to a reduction of about 50% in final biomass (Black and Wilkinson, 1963). Other studies demonstrated that early emerged seedlings grew taller than later ones, but these studies addressed germination delays of several weeks or months (Rice, 1990;Quintana et al., 2004;De Luis et al., 2008). In our experiment, the investigated plants that germinated 7 d later and grew together with barley were about 23% shorter at the end of their life cycle, compared to the controls. ...
Time of seedling emergence is an important step in the life cycle of annual plants because it may determine subsequent performance and success. Timing of emergence is especially critical to plant performance in habitats like arable fields which are subject to frequent disturbances. Within-season variation in timing of germination in the range of only a few days is typical for many arable weeds. However, since it is unclear whether such small deviations in germination date translate into fitness differences in the course of the life cycle, the aim of this paper was to quantify the effects of short germination delays on plant performance. We conducted two generalized randomized block experiments in an unheated greenhouse to study the impact of delayed germination (1, 2, 3 and 7 d) with and without competition, respectively, on the fitness of the arable weed species
Agrostemma githago
(L.). We expected that delayed germination significantly reduces fitness in terms of several life-history traits, and that the decrease of fitness is higher in the presence of competition. Under realistic conditions with competition through barley,
Agrostemma
plants with delayed germination of 7 d produced 54% fewer shoots, 57% less biomass, 52% fewer flowers, 36% lighter seeds and were 23% shorter as compared to control plants without delayed germination. Without additional stress through competition with barley this pattern was less pronounced. Thus, in the situation of interspecific competition, early emerging seedlings have biologically significant fitness advantages over later emerging seedlings of the same species.
... This species is hermaphroditic with entomogamous pollination (Rodríguez-Pérez 2005). Its seeds have a short dispersal distance, and the species seems to have a life cycle of about 15-20 years (De Luis and Raventós 2008). The species thrives in thermophilic scrubland with Rosmarinus officinalis and is often associated with pioneer plant situations or regressive succession after recurrent fires (Tison et al. 2014). ...
... Fires allow pioneer plants to develop by simultaneously opening up the environment and making the ecological niche available. The germination of H. marifolium is usually triggered after fires, then the population gradually disappears as the vegetation becomes denser (De Luis and Raventós 2008;Raventós et al. 2010;Gauthier et al. 2019). In some species, particularly in the Cistaceae family, seed germination is induced by high heat or other fire-related mechanisms such as smoke (Thanos et al. 1992;Santana et al. 2013). ...
In the context of a land development project, we carried out an experimental translocation before the proposal of mitigation hierarchy related to the project. By doing this early, we obtained results on the experimental translocation and thus better inform the measure proposed as part of the project. This project is likely to impact a large population of the plant species Helianthemum marifolium, which has a national protected status in France. We present here the pre-translocation phase, proposing different methodologies to better understand and prepare for a translocation. First, we studied the potential future distribution based on climate factors. Then, we sought to improve our knowledge of the local populations studied. To do this, we carried out pollinator surveys and a study of reproductive success. Finally, we presented the results of germination and cultivation tests, which enabled us to determine the mechanism for breaking dormancy and the most favourable substrate for growing, and we compared potential host sites regarding soil analyses. These different aspects allowed us to determine a protocol to be followed for a more significant translocation of this species. This case study illustrates requirements of the pre-translocation planning and can be used to inform future translocations of Helianthemum marifolium. The case study also presents methods other translocation practitioners can use to improve their protocols in the future.
... These temperatures are related to the rainfall period in autumn when germination often occurs (Espigares and Peco, 1993;Céspedes et al., 2012;Chamorro et al., 2017a). Early germination ensures appropriate root development to help plants withstand the harsh summer drought (De Luis et al., 2008). Likewise, the response of seeds to light can control the timing of germination in the field, a decisive factor for survival of the seedlings as well as for growth and fitness in subsequent life stages (Donohue et al., 2010). ...
... Specifically, we wondered if final germination was affected by temperature and light factors, and especially if the effect of light was temperature-dependent. Fire opens a narrow window free of competitors, where success depends on being the first to germinate (Verdú and Traveset, 2005;De Luis et al., 2008). According to this argument, species from fire-prone areas should germinate immediately after fire, regardless of the environmental conditions present. ...
Cistus species have seeds with hard coats which impose physical seed dormancy that can be released after seed scarification. In fire-prone habitats, the break of physical seed dormancy is usually related to the heat produced during fires. It is commonly accepted that most hard-seeded species, including those of the genus Cistus , are able to germinate under a wide range of temperatures in light as well as in darkness, once the seed becomes permeable. However, although many studies have focused on the release of physical dormancy only, a few have done so on the effect of environmental factors once dormancy is released. In this research, through a factorial experiment, we analysed the effects of light (light and darkness) and a range of temperatures (10, 15, 20, 25 and 30°C) on the seed germination of eight Cistus species after a heat shock. On average, almost 60% of the seeds did not germinate despite being viable, and this lack of germination increased with higher temperatures during the treatment. Although an idiosyncratic germination response emerged, temperature had a significant effect in all the species, reaching the highest levels of germination between 10 and 20°C. Light interacted with temperature in four cases by increasing the germination, especially under the least favourable temperatures. Environmental factors, such as temperature and light, appear to modulate the germination of the studied Cistus species after the release of physical seed dormancy.
... Such changes could likely shift the temporal window of germination. Timing of germination is important for establishment ( Quintana et al., 2004 ;De Luis et al., 2008 ). Consequently, the future plant community could be aff ected by variations in germination induced by changes in temperature and rainfall. ...
... When temperatures were low, germination was suppressed during the winter and did not resume until the following spring, which could reduce the risk of germination during the coldest period of the year. Frost causes severe mortality due to soil upheaval ( Quintana et al., 2004 ;De Luis et al., 2008 ;Gómez-Aparicio et al., 2008 ). Halimium ocymoides is a slow-germinating species (mean T 0 = 34 d, vs. mean T 0 = 21 d for the three Cistus [unheated seeds]), which indicates that its germination phase is likely to occur during winter and into spring. ...
PREMISE OF THE STUDY: Species differ in their temperature germination niche. Populations of a species may similarly differ across the distribution range of the species. Anticipating the impacts of climate variability and change requires understanding the differential sensitivity to germination temperature among and within species. Here we studied the germination responses of four hard-seeded Cistaceae seeders to a range of current and future temperatures.
METHODS: Seeds were collected at sites across the Iberian Peninsula and exposed or not exposed to a heat shock to break dormancy, then set to germinate under four temperature regimes. Temperatures were varied daily and seasonally, simulating the temperature range across the gradient, plus an increased temperature simulating future climate. Time to germination onset and cumulative germination at the end of each season were analyzed for the effects of temperature treatments, seasons, and local climate (temperature of the germination period, Tgp) at each site.
KEY RESULTS: Tgp was a significant covariate of germination in all species but Cistus populifolius. Temperature treatments significantly affected Cistus ladanifer, C. salviifolius, and Halimium ocymoides. Germination occurred in simulated autumn conditions, with little germination occurring at later seasons, except in unheated seeds of H. ocymoides. Exposure to a heat shock changed the sensitivity to temperature treatments and the relationships with Tgp.
CONCLUSIONS: Germination responses to temperature differ not only among species but also within species across their latitudinal range. The responses were idiosyncratic and related to the local climate of the population. This germination variability complicates generalizing the impacts of climate variability and climate change.
... Whether the benefits of differences in germination timing between invasive and native species change over time remains unclear. The majority of studies on this topic have been conducted over one season or one year only, while only few studies have explored the effects of differences in the timing of germination between alien and native species over multiple years (Young et al. 2001;De Luis et al. 2008;Vaughn and Young 2015). Evidence of the persistence of community effects associated with early germination by one or more species is contrasting, showing that the initial advantage of early germination increases or decreases over time (Verdú and Traveset 2005;Körner et al. 2008), or is perpetuated for several years (De Luis et al. 2008). ...
... The majority of studies on this topic have been conducted over one season or one year only, while only few studies have explored the effects of differences in the timing of germination between alien and native species over multiple years (Young et al. 2001;De Luis et al. 2008;Vaughn and Young 2015). Evidence of the persistence of community effects associated with early germination by one or more species is contrasting, showing that the initial advantage of early germination increases or decreases over time (Verdú and Traveset 2005;Körner et al. 2008), or is perpetuated for several years (De Luis et al. 2008). ...
Aims
Plant invasions represent a unique opportunity to study the mechanisms underlying community assembly rules and species distribution patterns. While a superior competitive ability has often been proposed as a major driver of successful plant invasions, its significance depends crucially on the timing of any competitive interaction. We assess whether a mismatch in germination phenology can favor the establishment of alien species, allowing them to exploit vacant niches where competition is low. As well as having important effects on the survival, growth and fitness of a species, asymmetric competition and potential soil legacies resulting from early or late germination can also impact on species recruitment. However, early or late germination comes at a cost, increases the risks of exposure to unfavorable conditions and requires an enhanced abiotic resistance if it is to lead to successful establishment.
Important Findings
While there are several anecdotal accounts of early and late germination for invasive species, there are limited comparative data with resident species growing under natural conditions. Available evidence from grassland communities indicates that a short-term germination advantage or priority (few days/weeks) provides invasive species with a strong competitive advantage over native species and is a critical factor in many invasions. While the exploitation of periods of low competition is a plausible mechanism for the successful establishment of many invasive plants, direct evidence for this strategy is still scarce. This is particularly true with regard to the exploitation of late germination niches. Consequently, long-term comparative monitoring of the germination phenology of invasive and native plants in situ is needed to assess its significance in a range of ecosystems and its impact on community dynamics.
... Seeders are supposed to germinate promptly in response to fire cues under a wide range of environmental conditions. This high capacity to germinate and emerge early in the first rainy season after a fire, regardless of other conditions, endows an ecological advantage because these species would be the first ones to establish (De Luis et al., 2008b). Furthermore, seedlings of seeders show traits that allow them to deal with water-limited and highly variable conditions (Vilagrosa et al., 2014). ...
... Germinating too early can result in seedlings being exposed to a high number of threats, but seeds that germinate too late are exposed to predation for longer periods (Donohue et al., 2010). In the Mediterranean, early germination may ensure the appropriate root development for facing up to summer drought (Moreno and Oechel, 1992;De Luis et al., 2008b) but also can lead to seedlings being exposed to frosts (Quintana et al., 2004) or unpredictable torrential rainfalls (De Luis et al., 2006). Therefore, a fine tuning between environmental conditions and germination patterns can improve plant fitness by ensuring seedling survival (Fenner and Thompson, 2005;Donohue et al., 2010). ...
Water availability regulates timing of germination, especially in those environments where it is a limiting factor. However, the water requirements for germination of most wild Mediterranean species are unknown. In this work we analysed the germination response to water stress of eight Cistaceae species with hard-coated seeds, which are typical for the Mediterranean shrublands. Seeds were exposed to a heat shock in order to overcome physical dormancy and then incubated under five water potentials (0, −0.2, −0.4, −0.6 and −0.8 MPa). Ungerminated seeds following these treatments were transferred to water in order to evaluate the recovery of germination. Additionally, at the end of the experiment, viability of still ungerminated seeds was examined. We analysed final germination percentage, time to reach 50% of the final germination (
t
50
), recovery of germination and seed viability in relation to water stress treatments. Furthermore, hydrotime analysis was performed; sensitivity to water stress, as characterized by Ψ
b
(50), was checked in relation to seed size of species. Overall, water stress delayed and decreased germination but species showed different germination sensitivities, which were not related to seed size. Recovery of germination was high after disappearance of water stress but seed viability decreased in some species. Consequently, post-fire germination of Cistaceae must be strongly regulated by water availability and their seeds can recover germination capacity when sufficient water is available after long periods of incomplete hydration. However, some seeds die during the wait.
... Instead we propose that in the case of early emergence after stand clear cutting, interspecific competition for the resources was low. Early emergence is known to benefit seedling growth [38,39]. In our study, thanks to the early establishment of their root and shoot systems, gorse seedlings may have been less sensitive to the interspecific competition that increased later. ...
... The strategy of regeneration that appeared in our results-the importance of the early emergence after a disturbance, sensitivity to water availability and the importance of the facilitation by nurse plants during dry episodes-is totally consistent with former results regarding the Mediterranean gorse, Ulex parviflorus [15,39]. As to the gorse regeneration niche, we showed evidence that P and water availability are important ecological factors for species regeneration. ...
The identification of an ecological niche specific to the regeneration phase has mobilised significant attention. However, the importance of the regeneration niche concept remains unclear. Our main objective was to study the existence of such a regeneration niche for a leguminous shrub, Ulex europaeus. This study was carried out in southwest France in the context of water and nutrient stresses (mainly phosphorus limitation) due to the presence of nutrient-poor sandy soils. We analysed the regeneration of the species from the germination of seeds and emergence of new seedlings until the seedlings reached young shrub size. Our design included a P fertilisation treatment. We also investigated microsite characteristics (micro-topography and vegetation development) as they can interact with meteorological conditions and determine water availability for seeds and seedlings. We found that P availability controlled seedling growth and the time necessary to reach young shrub size. Water availability appeared to impact the species germination and seedlings survival. We also found that P and water availability depended on the interactions between microsite characteristics and climatic variations. Finally we found evidence that P and water availability are important ecological factors shaping the regeneration niche of the species, but we found weak evidence that any microsite would be appropriate for the regeneration of the species in the long term. Future studies regarding regeneration niches need to distinguish more clearly the ecological factors important for regeneration (the regeneration niche per se) and the physical world where the seedlings appear and develop (the regeneration habitat).
... Despite occasional reproductive events without fire in some obligate seeding species (Nathan et al., 1999), the bulk of the effective reproduction in these species occurs after a fire when the plant dies, and thus they can effectively be considered semelparous with a single reproductive event per fire cycle and mostly with nonoverlaping generations. In fact, there is evidence of selection acting to favor early emergence in postfire seeding species (de Luis et al., 2008). The two life histories have consequences in the cohort structure (obligate seeding species form even-aged populations while resprouting species form multiple-cohort populations) and in the genetic variability and the evolutionary potential (obligate seeding species have shorter generation time and faster population turnover). ...
... In addition to delayed reproduction enforced by deep seed dormancy and germination stimulated by heat or smoke, traits expected to be selected in postfire seeders include early emergence and rapid seedling growth. These traits allow seedlings to quickly capture resources and become more competitive, and this can be adaptive for seedlings under crowded postfire conditions where recruitment is concentrated in a single point in time (de Luis et al., 2008). Concomitant with the evolution of postfire seeding, one might also expect selection for traits that enhance flammability. ...
There are two broad mechanisms by which plant populations persist under recurrent disturbances: resprouting from surviving tissues, and seedling recruitment. Species can have one of these mechanisms or both. However, a coherent framework explaining the differential evolutionary pressures driving these regeneration mechanisms is lacking. We propose a bottom-up approach in addressing this question that considers the relative survivorship of adults and juveniles in an evolutionary context, based on two assumptions. First, resprouting and seeding can be interpreted by analogy with annual versus perennial life histories; that is, if we consider disturbance cycles to be analogous to annual cycles, then resprouting species are analogous to the perennial life history with iteroparous reproduction, and obligate seeding species that survive disturbances solely through seed banks are analogous to the annual life history with semelparous reproduction. Secondly, changes in the selective regimes differentially modify the survival rates of adults and juveniles and thus the relative costs and benefits of resprouting versus seeding. Our approach provides a framework for understanding temporal and spatial variation in resprouting and seeding under crown-fire regimes. It accounts for patterns of coexistence and environmental changes that contribute to the evolution of seeding from resprouting ancestors.
... The passage of seeds through the digestive tract can promote chemical or physical scarification, which can remove parts of the fruit responsible for mechanical and chemical dormancy (Baskin and Baskin, 2004), thus eliminating inhibiting factors for germination and facilitating the activation of metabolic processes (Traveset and Verdú, 2002). This process may have implications for plant recruitment and establishment, since early germination may increase competitive fitness (Verdú and Traveset, 2005;Traveset et al., 2007;De Luis et al., 2008). ...
The interaction between fish and plants in Amazon floodplain is fundamental for the maintenance of frugivorous fish and tree communities. The viability of seeds after passing through the digestive tract of fish is a central factor for seed dispersal since it can influence colonization and regeneration of these environments. Our study investigated the seed dispersal by frugivorous fish in a flooded forest in the Central Amazon. We also evaluated the seed germination speed after passage of the digestive tract of fish and how the size of fish and the seeds can influence the dispersion of tree seeds in floodplains. A total of 5,012 seeds from 49 plant species were found in the digestive tracts of 11 frugivorous fish species. The length and weight of the frugivorous fish were positively related to the size of seeds in the digestive tract. The germination of the seeds removed from the fish varied between species. The passage of the seeds of the different plant species through the digestive tracts of the fish did not significantly increase the germination speed. Considering the anthropogenic pressures present in these environments , we can expect that a reduction in body size for some species of fish, due to overexploitation, may have negative consequences for some tree species that are dispersed mainly via ichthyochory.
... While more seedlings emerging earlier might give species an interspecific competitive advantage leading to a higher abundance of a species in a plant community, higher seedling densities might induce increased seedling mortality due to higher intraspecific competition (Fenner and Thompson, 2005). Several studies showed that a reduced emergence time fosters plant growth faster and flower production per plant (de Luis et al., 2008;Orrock and Christopher, 2010;Verdú and Traveset, 2005). Still, in the long run, stimulation of emergence through changes in the seed's environment may lead to a depletion of the soil seed bank that species developed as a bet-hedging strategy against short-and long-term environmental stochasticities (Hölzel and Otte, 2004), which are particularly given with grazing (Fenner and Thompson, 2005). ...
Sheep function as effective endozoochorous seed vectors in grasslands. Recent laboratory-based studies showed that this important function can be impaired by macrocyclic lactone anthelmintics, which are used to control parasites and enter into the environment mainly via faeces; however, there is a lack of in vivo studies. We conducted a seed-feeding experiment with sheep that included four temperate grassland species from four different families (Achillea ptarmica, Asteraceae; Agrostis capillaris, Poaceae; Dianthus deltoides, Caryophyllaceae; Plantago lanceolata, Plantaginaceae). A series of three feeding trials was carried out after one of two groups of sheep received a single administration of a common oral formulation of the macrocyclic lactone moxidectin. Faeces were collected to determine seedling emergence rate and emergence timing as well as moxidectin concentration via HPLC. Seedling emergence differed significantly between the anthelmintic-treated sheep and the control group. This impact depended on time of seed uptake after anthelmintic administration. Number of emerging seedlings was significantly reduced (27.1 %) when faeces moxidectin concentrations were high (on average 3153 ng g−1; 1 d post treatment) and significantly increased (up to 68.8 %) when moxidectin concentrations were low (≤86 ng g−1; 7, 14 d pt). Mean emergence time was significantly lowered at low moxidectin concentrations. These results demonstrate dose-related effects of deworming on seedling emergence which might affect endozoochory and eventually plant population dynamics in grasslands.
... On the other hand, seeder species with transient soil seed banks would be expected to disperse before the fire season to maximally benefit from the current seed crop in case of fire. If chilling would be required, this would just delay the germination in time until late winter or early spring, which might compromise establishment (Luis et al. 2008;Moreno et al. 2011), but would not affect dispersal temporal patterns. Obligate resprouter species (R + S −) with transient seed soil seed banks would be expected to disperse before the wet season would start in autumn. ...
Background
Mediterranean shrublands are composed of species that have different regeneration strategies after fire and soil seed bank types. However, differences over the years in seed dispersal temporal and spatial patterns of the various plants composing a community have been little investigated. Here, we studied the temporal and spatial patterns of seed dispersal in four shrubs of an old (> 40 years) shrubland in central Spain. Three of them are seeders ( Cistus ladanifer , Erica umbellata , and Salvia rosmarinus ), and one is a resprouter ( Erica arborea ); the first two have persistent soil seed banks, and the latter two, transient. A 15 × 10 m plot was chosen and divided into a 0.5 × 0.5 m grid, where plant cover and density were measured. At 106 quadrats, seed traps were set and periodically (1–2 monthly) monitored for 3 years.
Results
S. rosmarinus dispersed in late spring-early summer, E. arborea dispersed during the summer, and C. ladanifer and E. umbellata dispersed from early summer to nearly late spring of the next year. Globally, seeds were being dispersed all year round. The seed crop size of a given species varied between years, although species differed in the year their seed crop was largest, despite large differences in climate. Seed rain and plant cover of each species were poorly related in terms of the variance explained by the models. Semivariogram analysis showed that seed dispersal expanded beyond that of the plant cover of each species by a few meters. No association between seed crop size and spatial dependence was ascertained. While species dispersal in space tended to be negatively related to one another, E. arborea seeds tended to dominate underneath the majority of the other species.
Conclusions
S. rosmarinus dispersed before the fire season, which is consistent with seeds avoiding fire while on the plant; C. ladanifer and E. umbellata dispersed mostly after the fire season, which is coherent with a bet-hedging strategy against seed predators; E. arborea dispersed before the rainy season, which is expected for a plant that germinates readily after imbibition. Seed dispersal in time was compatible with the type of soil seed bank and post-fire regeneration of the species. The evidence of such a relationship with spatial patterns was weak. The dominance of E. arborea seeds underneath most of the other species suggests that this mid-successional species might dominate when openings form due to the deaths of standing plants of the seeders between two fires, given their lower longevity.
... Several studies in temperate environments have found a positive effect of early germination and emergence on seedling performance in both annual and perennial species, mainly through enhancing seedling growth and fecundity (Verdú and Traveset, 2005). Early emergence in the growing season may confer a competitive advantage and/or a longer duration of seedling growth and reproduction before the onset of unfavourable conditions, resulting in larger, more competitive seedlings that can survive harsh conditions, such as low light and low water availability (Miller et al., 1994;Jones et al., 1997;Seiwa, 1998;De Luis et al., 2008;Mercer et al., 2011;Afonso et al., 2014). However, other studies have demonstrated that early germination and emergence were associated with low seedling survival, because it increased the probability of exposure to early-season climatic hazards, such as drought, waterlogging (soil water saturation) and frosts (Quintana et al., 2004;Weekley et al., 2007;Akiyama and Ågren, 2014;Center et al., 2016). ...
Background and aims:
Timing of seed dispersal determines the environmental conditions that plants face during early life stages. In seasonal environments, selection is expected to favor dispersal timing that is matched to environmental conditions suitable for successful recruitment. Our aim was to test whether the timing of seed dispersal influences seedling establishment success in two populations of Euterpe edulis that are located at contrasting altitudes, that have different seed-dispersal phenologies, and that are subjected to distinct climatic conditions.
Methods:
We sowed E. edulis seeds in contrasting altitudes on different dates, and monitored seed germination, emergence, and seedling establishment at each altitude over four years. At the high-altitude site, five seed-dispersal cohorts were established during the natural dispersal period. At the low-altitude site, three seed-dispersal cohorts were established during the natural dispersal, and two were established either before or after natural dispersal.
Key results:
At the high-altitude site, seed-dispersal timing did not affect seed germination, seedling emergence, or seedling establishment success. In contrast, at the low-altitude site, late seed dispersal near the end of the wet season resulted in a lower probability of seedling establishment, possibly due to the exposure of seeds, germinants and seedlings to unfavorable drought conditions. In addition, at the low-altitude site, natural seed-dispersal period was poorly matched to favorable environmental conditions for seedling establishment.
Conclusions:
The greater effect of seed-dispersal timing on seedling establishment at the low-altitude site is likely related to a more seasonal and drought-prone environment that favors a restricted period of seed dispersal. The magnitude of the effect of dispersal timing on seedling establishment success was modulated by environmental conditions that vary across altitude. Furthermore, reproductive phenology appears to be exposed to more intense selection at the lower limit of altitudinal range, due to a more restrictive window of opportunity for successful seedling establishment.
... Scientists agree that the early growth period is a crucial time for plants, which can affect their whole life. It is not only important to ensure that the soil is well prepared but also that it is rich in microorganisms that can enhance the growth of young plants such as raspberry seedlings and protect them from pathogens that are present in the soil [48][49][50]. Soilborne pathogens can be transported from the nursery to newly set up plantations, and from soil to leaves by soil splash that periodically occurs, e.g., during the rain [51,52]. The early effect of selected strains of bacteria on the growth of raspberry plants varied depending on the phytopathogen contamination variant and naturalization strategy. ...
The current study focuses on the optimization of bacterial growing medium composition, including the carbon and nitrogen source in different concentrations, the pH value of the medium and the temperature. Optimization was performed for four environmental bacterial isolates belonging to the genera Arthrobacter, Pseudomonas and Rhodococcus, which were previously obtained from wild raspberries. These bacteria proved to be potent antagonists against certain fungal and fungal-like plant pathogens. Furthermore, three preservation methods and three sample preparation techniques were evaluated. In addition, a prebiotic supplementary blend based on previous research was tested. The research included a pot experiment to estimate the influence of bacterial cultures on the growth of plant shoots and roots, on the soil enzymatic activity and the content of macronutrients, minerals and nitrogen in the soil depending on the naturalization strategy. The best carbon and nitrogen source were chosen. The addition of a supplementary blend resulted in the increased growth of two bacterial isolates. Bacterial inoculum applied to the roots and watering resulted in increased shoot mass in objects infected with plant pathogens, although in plants without the pathogen infection, bacterial inoculum resulted in the decreased mass of plants. Naturalization strategy should be matched to the pathogens present at plantations.
... The main difference between both years was that the spring of 2017 was drier than the spring of 2015. It is possible that seedlings that emerge in average and wet springs may be more drought-resistant by developing larger and deeper roots during the wet season than seedlings that emerge in a dry spring (Castro 2006;De Luis et al. 2008). Deep and extensive rooting allows plants to avoid drought stress and access to more water resources during the summer drought (Padilla and Pugnaire 2007;Cuesta et al. 2010a). ...
Planted woodland islets can provide seeds for restoring forest ecosystems in Mediterranean old fields lacking seed sources, but other factors than seed arrival can also hinder the establishment of woody species. We experimentally examined factors affecting the emergence, survival, growth, and recruitment of holm oak (Quercus ilex) seedlings juveniles from 25-year-old 100-m2 oak woodland islets planted in a Mediterranean old field. Wet springs and summers increased seedling emergence and survival. Distance to the islets per se did not affect seedling performance. However, emergence and survival increased in microsites close to the islets in less sun-exposed orientations of the islets and far from the islets in more sun-exposed orientations. Damage by wild boar reduced emergence, and unsheltered seedlings had 26% lower survival than sheltered ones. Herb community biomass and light reduction by herbs increased with distance from nearest islet; the sparse herb cover around islets was due to competition from woodland islets, not to herbivory. There was a mismatch between the pattern of seedling survival and how the abundance of naturally recruited oaks varied with distance from the nearest islet; this suggests that other drivers can counteract the spatial pattern of seedling survival. We conclude that natural regeneration of Q. ilex in old fields from planted woodland islets is slow (5.7 seedlings ha-1 yr-1) due to acorn and seedling predation, and drought during spring and summer. Despite their small size, planted islets affected survival of oak juveniles depending on the orientation and distance relative to the islets.
... We found this same positive correlation, but between the emergence of the first year and recruitment at the end of the fourth year post-fire ( Fig. 3). This reinforces the idea that emerge early gives the plants a competitive advantage (De Luis et al. 2008) and what happens during the first year post-fire is critical for the long-term fate of the populations of these species. However, within this overall response to the fire, we were able to distinguish differences among species. ...
La disponibilidad hídrica se considera como el factor más limitante en el crecimiento y la distribución de las especies vegetales presentes en los ecosistemas mediterráneos, donde los rigores del clima imponen una doble adversidad a los sistemas biológicos: la escasez de precipitaciones y la irregularidad de las mismas. Por su parte, el fuego ha sido una perturbación recurrente en los ecosistemas mediterráneos durante los últimos miles de años, modelando su paisaje y las formaciones vegetales presentes en los mismos. Sin embargo, se espera que las condiciones en ambos factores varíen en el futuro, ya que con el cambio climático se proyecta un aumento en la frecuencia e intensidad de los periodos de sequía, lo cual unido a la elevación de las temperaturas provocará un aumento en el riesgo de incendios y en la ocurrencia de los mismos. En la presente tesis doctoral se muestran los resultados obtenidos a partir de un experimento de manipulación del régimen de precipitaciones llevado a cabo durante cinco años en un matorral mediterráneo del centro de la Península Ibérica. Para ello se instaló en campo un sistema de riego y cubiertas de exclusión de lluvia automatizadas, con las que se simularon varios tratamientos de sequía antes y después de llevar a cabo una quema experimental. El objetivo principal de este trabajo ha sido estudiar y entender mejor la respuesta frente a la sequía de la vegetación presente en estos ecosistemas de matorral, tanto en su estado maduro (antes del fuego) como en su fase juvenil (después del fuego). El estudio se ha realizado desde una perspectiva de grupos funcionales, intentando discernir si la respuesta frente a la sequía es diferente o no en especies con distinta estrategia de regeneración (especies semilladoras frente a rebrotadoras). Así mismo, el desarrollo del trabajo se ha realizado de una forma integral, estudiando desde la ecofisiología y la respuesta funcional a nivel de planta hasta la estructura y composición de la comunidad vegetal en su conjunto, pasando por la dinámica de las distintas poblaciones de plantas. La tesis doctoral se ha estructurado en cuatro capítulos en formato de artículos científicos: En el capítulo 1, “Modificación de los patrones de lluvia en un matorral mediterráneo: diseño del sistema, respuestas de las plantas y quema experimental”, se describe el diseño y la implantación del experimento de manipulación del régimen de precipitaciones. Los objetivos de este capítulo fueron evaluar el efecto de estas manipulaciones sobre la humedad del suelo y el microambiente de las parcelas, analizar las primeras respuestas de las plantas frente a la sequía antes de la quema experimental y reportar las características del fuego registradas en dicha quema. En el capítulo 2, “Diferencias en los rasgos morfo-fisiológicos de la hoja reflejan la respuesta del crecimiento frente a la sequía en una especie mediterránea semilladora pero no en una rebrotadora”, se presenta la respuesta de dos especies con diferentes características foliares y estrategias de regeneración (la semilladora Cistus ladanifer y la rebrotadora Erica arborea) frente a la sequía durante una estación de crecimiento antes del fuego. Los objetivos de este trabajo fueron entender mejor los mecanismos funcionales que las plantas utilizan para hacer frente a la sequía y determinar los principales rasgos morfo-fisiológicos de la hoja relacionados con el crecimiento de la planta. Una vez realizada la quema experimental de las parcelas de estudio, en el capítulo 3, “Los ambientes post-fuego son favorables para el funcionamiento de los arbustos mediterráneos semilladores y rebrotadores, incluso bajo sequía”, se describe la respuesta ecofisiológica frente a la sequía en las principales especies leñosas de la comunidad (Cistus ladanifer, Erica arborea, Erica scoparia y Phillyrea angustifolia) durante los tres primeros años después del fuego. Los objetivos de este capítulo fueron comparar la respuesta funcional de las plántulas y rebrotes respeto a las plantas adultas (es decir, quemado frente a no quemado), estudiar el efecto de la sequía post-incendio en estas respuestas e intentar discernir si existía o no una sensibilidad diferente entre especies con distinta estrategia de regeneración (semilladoras frente a rebrotadoras). Finalmente, en el capítulo 4, “Dinámicas post-incendio a corto plazo en un matorral mediterráneo sometido a una sequía experimental”, se muestra la dinámica de regeneración de la comunidad vegetal presente en la zona de estudio durante los cuatro primeros años después del fuego. En este caso, el objetivo del estudio fue evaluar el efecto de la sequía post-incendio en la dinámica poblacional de las principales especies leñosas semilladoras (Cistus ladanifer, Rosmarinus officinalis y Genista hirsuta) y rebrotadoras (Erica arborea, Erica scoparia y Phillyrea angustifolia), averiguar si la estrategia de regeneración (semilladoras frente a rebrotadoras) jugaba un papel clave en la recuperación de las especies y evaluar si los cambios a nivel poblacional, en caso de producirse, afectaban finalmente a la configuración de la comunidad en su conjunto. En resumen, los resultados obtenidos en la presente tesis doctoral nos muestran que el matorral mediterráneo presenta una alta resiliencia frente a la sequía, tanto antes como después del fuego, aunque algunas especies (especialmente las semilladoras) pueden verse afectadas negativamente por dicho factor. De hecho, hemos visto que los cambios que las plantas sufren a nivel funcional, pueden traducirse posteriormente a nivel poblacional y terminar afectando significativamente a la comunidad en su conjunto. Por ello, creemos que experimentos como el realizado en esta tesis, aun siendo complejos, son claves para estudiar y entender de una manera global el papel de la sequía y el fuego en los ecosistemas mediterráneos, ya que nos permiten abordar la respuesta de las plantas desde distintos niveles de análisis y a lo largo de diferentes momentos en su ciclo vital. Además, ahondar en nuestro conocimiento acerca de los efectos de la sequía y el fuego sobre la vegetación puede ser clave para entender y prever los efectos del cambio climático en los ecosistemas mediterráneos, puesto que las proyecciones nos indican que ambos factores jugarán un papel determinante en la futura composición, estructura y funcionamiento de muchos ecosistemas en dichas regiones del globo.
... Many of campo rupestre's species resprout vigorously and flower rapidly, which creates an abundance of seeds soon after fire , overcoming the limitations of a poor seedbank. Early emergence allows seedlings to take advantage of reduced competition and increased resource availability and have long-term effects on plant fitness (de Luis et al. 2008). In our study, most species showed earlier germination of only a few days. ...
Fire is an important disturbance in terrestrial ecosystems and plays a key role in the germination process and seedling establishment of many species. In grassland ecosystems, seeds normally tolerate heat-shocks associated with low intensity fires but are negatively affected by higher heat doses. Additionally, smoke-stimulated germination is not commonly recognized as important in neotropical grasslands. This may result from a negative relationship between the ability to resprout after fire and fire-stimulated germination ability, as many species in these grasslands regenerate well after fire by resprouting. To ascertain the role of heat and smoke in the post-fire germination response of campo rupestre vegetation, we exposed seeds of nine species (that regenerate after fire by resprouting) to various treatments related to fire (heat, smoke, and heat plus smoke) and analysed their germination behaviour. Our results suggest that these species have high seed germination in the absence of specific dormancy breaking conditions and/or that stimulated germination triggered by fire-related cues is not common. Additionally, while seeds from some species can withstand temperatures of 80 °C for 5 min without affecting germination, most species are negatively affected by higher heat doses. However, our results suggest an important role of smoke enhancing germination rate (speed) of campo rupestre species. In view of the characteristics of campo rupestre environmental conditions and vegetation, we provide a novel outlook of enhanced germination rate by smoke as an important mechanism for seed regeneration after fire of campo rupestre’s species that resprout, particularly for seeds resulting from post-fire seed dispersion.
... Early-emerging seedlings feature higher growth rates than those emerging later (de Luis, Verdú, & Raventós, 2008;Orrock & Christopher, 2010;Trimble & Tryon, 1969), which may be due to the fact that early emergence implies exposure to higher light availability and thus higher carbon gain (Augspurger & Bartlett, 2003), with photosynthetic activity peaking before canopy closure (Augspurger, Cheeseman, & Salk, 2005). Indeed, higher light availability prior to the development of the forest canopy is another advantage that early-emerging seedlings benefit from (Winkler, Hülber, & Hietz, 2005). ...
Global warming is expected to result in earlier emergence of tree seedlings that may experience higher damages and mortality due to late frost in spring. We monitored emergence, characteristics, and survival of seedlings across ten tree species in temperate mixed deciduous forests of Central Europe over one and a half year. We tested whether the timing of emergence represents a trade‐off for seedling survival between minimizing frost risk and maximizing the length of the growing period. Almost two‐thirds of the seedlings died during the first growing period. The timing of emergence was decisive for seedling survival. Although seedlings that emerged early faced a severe late frost event, they benefited from a longer growing period resulting in increased overall survival. Larger seedling height and higher number of leaves positively influenced survival. Seedlings growing on moss had higher survival compared to mineral soil, litter, or herbaceous vegetation. Synthesis. Our findings demonstrate the importance of emergence time for survival of tree seedlings, with early‐emerging seedlings more likely surviving the first growing period. In Central European temperate forests, the timing of seedling emergence determines survival and represents a trade‐off between decreasing the frost risk and increasing the length of the growing period. Early emerging tree seedlings benefited from a longer growing period resulting in increased survival, although they faced a severe late frost event.
... On the other hand, as the temperature and growing season declined with increasing altitude, seeds of the populations growing at high altitude must be adapted to earlier germination under low temperature to maximize the length of growing season to ensure their growth and reproduction (Körner 2003;Giménez-Benavides et al. 2005;Montesinos-Navarro et al. 2011). Interestingly, De Luis et al. (2008) detected that fitness (survival, growth, or fecundity) benefits acquired by early seedling emergence could be maintained throughout the life cycle of four woody species. ...
Key message
Seeds of a relict tree species collected from high latitudes were more sensitive to temperature and warming could accelerate germination.
Abstract
Seed germination is a crucial process in a plant life cycle and is highly vulnerable to environmental change. Studying among-population variation in seed germination in response to environmental and geographic gradients is an important tool, allowing us to understand how plants adapt to different environmental conditions and to predict population dynamics under future climate change. Here, we collected seeds of Euptelea pleiospermum, a relict broad-leaved tree species, from six provenances along latitudinal and altitudinal gradients across its distribution in China. We investigated variation in seed germination percentage and germination timing of seeds from these different origins (low, middle, and high latitudes/altitudes) at three incubation temperatures (15 °C, 20 °C and 25 °C). The key results were as follows: first, seeds collected from high latitudes were more sensitive to temperature and was likely to benefit from the higher incubation temperature with increasing germination percentage and shorter germination timing; second, for seeds across latitudes, germination percentage of central populations was lower than that of marginal populations; seed origin and its interaction with temperature were the major drivers of germination percentage variation; germination timing was significantly affected by incubation temperature, and warming could accelerate germination; third, for seeds across altitudes, both germination percentage and germination timing were not significantly affected by seed origin, incubation temperature, or their interaction. Our results indicate that climate warming may influence the population dynamics of relict tree species by altering their seed germination patterns, especially for the leading-edge populations along latitudinal gradient. It is vital to take inter-population variation across species’ geographic distribution into account when estimating the impact of environmental changes on plant species’ distribution and population persistence.
... For example, during intense fires, temperatures at the soil surface can exceed 900°C and within 2 cm temperatures can decrease to 150°C (Odion and Davies 2000), or to 80°C and stay above 60°C for 1 h at a depth of 4 cm (Newton et al. 2006). Most seed banks are concentrated in the top 5 cm of the soil (Roberts 1981;Simpson et al. 1989); however, the tiny seeds of the Cistaceae are unable to emerge from depths of more than 2-3 cm (Odion and Davies 2000;De Luis et al. 2008). The temperatures experienced by buried seedbanks during fires are important for post-fire germination since low intensity fires or high depths may not provide the adequate heat to break physical dormancy in seeds. ...
Background: Species of the Cistaceae family have hard-coated seeds and consequently require scarification for germination. It is widely assumed that the high temperature caused by fire is a scarifying agent that triggers seed germination in the Cistaceae. However, to date there is insufficient knowledge regarding species, populations and diverse variables associated with germination to consider such a fire-trigger generally applicable.
Aims: We tested the relationship between exposure to fire and germination in 10 species of the Cistaceae family to identify the modulating role of species.
Methods: We quantified after different heat treatments the germination and seed viability in 10 species of the Cistaceae from the western Mediterranean. Seeds of species of Cistus, Fumana, Halimium, Helianthemum and Tuberaria were germinated after being exposed to different heat treatments for 10 minutes. Final germination percentage, t50 and seed viability were determined.
Results: Heat treatment increased germination in all except the species of Helianthemum, however, the rate of increase was dependent on species. Germination speed (t50) was less affected by heat than final germination, and seed viability did not decrease except for H. hirtum, which was damaged by the highest temperature applied.
Conclusions: Most of the species showed high tolerance and a positive response to heat although germination patterns were idiosyncratic of each species. This work evidences the wide range of germination responses to heat within Cistaceae, and consequently the differential role of fire within this plant family.
... The underlying rationale is that the first seeds to appear have more time to develop and face the upcoming unfavorable seasons (cold winters or dry summers) with a bigger root system that allows for more extensive soil exploration, and longer and thicker hypocotyl or stems that protect against damaging temperatures (Woods et al. 2014). This hypothesis contrasts with the safe site hypothesis, in that it postulates that the spatial arrangement of seedlings does not ultimately drive recruitment, but that the date of emergence within a window of opportunity plays a crucial role (de Luis et al. 2008). ...
... In accordance with this, we found a positive correlation between emergence in the first year and recruitment at the end of the fourth year after fire in all seeder species, despite the implemented drought treatments. This supports earlier findings by Moreno et al. (2011) and reinforces the idea that emerging early gives the plants a competitive advantage (De Luis et al., 2008), in such a way that what happens during the first year post-fire is critical for the long-term fate of the populations of these species. Therefore, since population controls rested largely on emergence, not so much on survival and subsequent recruitment, further understanding is needed about how emergence is controlled under variable rainfall patterns. ...
In fire-prone ecosystems, changes in rainfall after fire could differentially affect seeders and resprouters, thus leading to long-lasting impacts on the vegetation. Climate change in the Mediterranean region is projected to reduce precipitation, expand the summer drought and increase fire danger. Understanding the sensitivity to changes in rainfall during the post-fire regeneration stage is critical to anticipate the impacts of climate change on Mediterranean-type areas of the world. Here, we investigated how species differing in post-fire regeneration strategy (seeders vs resprouters) responded to rainfall changes in a Cistus-Erica shrubland of central Spain. Drought treatments were implemented using a system of automatic rainout shelters with an irrigation facility before (one season) and after (four years) burning a set of experimental plots. Treatments applied were: environmental control (natural rainfall), historical control (mimicking the long-term rainfall), moderate drought (−25% rainfall), and severe drought (−45% rainfall). Plant demography and vigour (main woody shrubs), as well as abundance (shrubs and herbs) were monitored during the first four years after fire. The first post-fire year was the key period for the recovery of seeders (Cistus ladanifer and Rosmarinus officinalis), and their recruitment, cover and size significantly decreased with drought. However, density four years after fire was larger than unburned and it was significantly correlated with emergence during the first year, indicating that population controls were more on emergence than on establishment. In contrast, resprouters (Erica arborea, Erica scoparia and Phillyrea angustifolia) were hardly affected by drought. Plant community dynamics in the burned control plots progressively converged with the unburned ones, while that in the drought-treated plots lagged behind them, maintaining a higher cover, richness and diversity of herbs. This post-fire “herbalization” due to drought might facilitate an untimely fire, before seeders would reach sexual maturity, which could have major implications for the maintenance of the community.
... In the case of E. australis, the heat shock increased germination sensitivity to temperature, which was against our expectations. Fire generates open environments suitable for plant establishment, where earlier germination would be advantageous to increase fitness (Verdú and Traveset, 2005;De Luis et al., 2008). According to this, after fire, species from fireprone areas must germinate rapidly, and have a broader tolerance to environmental factors such as temperature, water or light, which should become less important as germination controls. ...
In seasonal climates, germination timing is mainly controlled by temperature, especially in species with physiological seed dormancy. The germination response to temperature may, however, vary among populations across the distribution range of species. Understanding how populations along climate gradients vary in their sensitivity to temperature is important for determining their vulnerability to climate variability and change. Here, we investigated the germination response of two Erica species with physiological seed dormancy ( E. australis and E. umbellata ) to changes in temperature throughout the seasons (simulated autumn through to spring) and to the local climate in six localities across a latitudinal gradient in western Iberia. Effects were studied with and without exposing the seeds to a heat shock. The local climate of seed provenance emerged as a key factor in modifying the germination sensitivity to germination temperature and their variation through the seasons. Although each species showed idiosyncratic germination responses to temperature treatments and across the gradient, germination of both species was sensitive to warmer temperatures and to a heat shock. Both showed similar seasonal germination patterns: as we moved from south to north, populations tended to have a larger germination peak in spring, which was greater at colder temperatures. We conclude that rising temperatures associated with climate change will affect these species, particularly at their northern ranges, where many seeds will remain dormant during warmer winters. Arguably, models aiming at assessing climate change impacts in these species need to include such variability across latitude.
... competition, seedling herbivory) are reduced ( Bond and van Wilgen, 1996;Keeley and Fotheringham, 2000;Nelson et al., 2012), thus promoting effective recruitment. In addition, germinating late after a fire may prevent recruiting plants from reaching maturity before the next fire event, compromising their reproductive potential ( McMaster and Zedler, 1981;Enright et al., 1998) and, hence, their fitness ( de Luis et al., 2008). On the other hand, less attention has been paid in the scientific literature to the role of negative signals, such as allelochemicals, that can also regulate post-fire seed germination (e.g. ...
In fire-prone ecosystems, many plant species have specialized mechanisms of seed dormancy that ensure a successful recruitment after fire. A well-documented mechanism is the germination stimulated by fire-related cues, such as heat shock and smoke. However, less is known about the role of inhibitory germination signals (e.g. allelopathy) in regulating post-fire recruitment. Plant leachates derived from the unburned vegetation can enforce dormancy by means of allelopathic compounds, acting as a signal of unfavourable (highly competitive) niche for germination in pyrophyte species. Here, we assessed the separate effects of heat shock and plant leachates on seed germination of Drosophyllum lusitanicum, an endangered carnivorous plant endemic to Mediterranean fire-prone heathlands. We performed a germination experiment in which seeds were subjected to three treatments: (1) 5 min at 100 °C, (2) watering with plant leachate, and (3) control. Germination rate and seed viability was determined after 63 days. Heat shock stimulated seed germination in D. lusitanicum while plant leachates had inhibitory germination effects without reducing seed viability. Thus, both positive and negative signals could be involved in its successful post-fire recruitment. Fire would break seed dormancy and stimulate seed germination of D. lusitanicum through high temperatures, but also by eliminating allelochemical compounds from the soil. These results help to understand the population dynamics patterns found for D. lusitanicum in natural populations, and highlight the role of fire in the ecology and conservation of this endangered species. Seed dormancy imposed by plant-derived leachates as an adaptive mechanism should be considered more in fire ecology theory.
... The underlying rationale is that the first seeds to appear have more time to develop and face the upcoming unfavorable seasons (cold winters or dry summers) with a bigger root system that allows for more extensive soil exploration, and longer and thicker hypocotyl or stems that protect against damaging temperatures (Woods et al. 2014). This hypothesis contrasts with the safe site hypothesis, in that it postulates that the spatial arrangement of seedlings does not ultimately drive recruitment, but that the date of emergence within a window of opportunity plays a crucial role (de Luis et al. 2008). ...
Over the past 15 years, 3 million hectares of forests have been converted into shrublands or grasslands in the Mediterranean countries of the European Union. Fire and drought are the main drivers underlying this deforestation. Here we present a conceptual framework for the process of fire-induced deforestation based on the interactive effects of fire and drought across three hierarchical scales: resistance in individuals, resilience in populations, and transitions to a new state. At the individual plant level, we review the traits that confer structural and physiological resistance, as well as allow for resprouting capacity: deforestation can be initiated when established individuals succumb to fire. After individuals perish, the second step toward deforestation requires a limited resilience from the population, that is, a reduced ability of that species to regenerate after fire. If individuals die after fire and the population fails to recover, then a transition to a new state will occur. We document trade-offs between drought survival and fire survival, as embolism resistance is negatively correlated with fire tolerance in conifers and leaf shedding or drought deciduousness, a process that decreases water consumption at the peak of the dry season, temporally increases crown flammability. Propagule availability and establishment control resilience after mortality, but different hypotheses make contrasting predictions on the drivers of post-fire establishment. Mycorrhizae play an additional role in modulating the response by favoring recovery through amelioration of the nutritional and water status of resprouts and new germinants. So far, resprouter species such as oaks have provided a buffer against deforestation in forests dominated by obligate seeder trees, when present in high enough density in the understory. While diversifying stands with resprouters is often reported as advantageous for building resilience, important knowledge gaps exist on how floristic composition interacts with stand flammability and on the "resprouter exhaustion syndrome," a condition where pre-fire drought stress, or short fire return intervals, seriously restrict post-fire resprouting. Additional attention should be paid to the onset of novel fire environments in previously fire-free environments, such as high altitude forests, and management actions need to accommodate this complexity to sustain Mediterranean forests under a changing climate.
... The underlying rationale is that the first seeds to appear have more time to develop and face the upcoming unfavorable seasons (cold winters or dry summers) with a bigger root system that allows for more extensive soil exploration, and longer and thicker hypocotyl or stems that protect against damaging temperatures (Woods et al. 2014). This hypothesis contrasts with the safe site hypothesis, in that it postulates that the spatial arrangement of seedlings does not ultimately drive recruitment, but that the date of emergence within a window of opportunity plays a crucial role (de Luis et al. 2008). ...
Over the past 15 years, 3 million hectares of forests have been converted into shrublands or grasslands in the Mediterranean countries of the European Union. Fire and drought are the main drivers underlying this deforestation. Here we present a conceptual framework for the process of fire-induced deforestation based on the interactive effects of fire and drought across three hierarchical scales: resistance in individuals, resilience in populations, and transitions to a new state. At the individual plant level, we review the traits that confer structural and physiological resistance, as well as allow for resprouting capacity: deforestation can be initiated when established individuals succumb to fire. After individuals perish, the second step toward deforestation requires a limited resilience from the population, that is, a reduced ability of that species to regenerate after fire. If individuals die after fire and the population fails to recover, then a transition to a new state will occur. We document trade-offs between drought survival and fire survival, as embolism resistance is negatively correlated with fire tolerance in conifers and leaf shedding or drought deciduousness, a process that decreases water consumption at the peak of the dry season, temporally increases crown flammability. Propagule availability and establishment control resilience after mortality, but different hypotheses make contrasting predictions on the drivers of post-fire establishment. Mycorrhizae play an additional role in modulating the response by favoring recovery through amelioration of the nutritional and water status of resprouts and new germinants. So far, resprouter species such as oaks have provided a buffer against deforestation in forests dominated by obligate seeder trees, when present in high enough density in the understory. While diversifying stands with resprouters is often reported as advantageous for building resilience, important knowledge gaps exist on how floristic composition interacts with stand flammability and on the “resprouter exhaustion syndrome,” a condition where pre-fire drought stress, or short fire return intervals, seriously restrict post-fire resprouting. Additional attention should be paid to the onset of novel fire environments in previously fire-free environments, such as high altitude forests, and management actions need to accommodate this complexity to sustain Mediterranean forests under a changing climate.
... 20 years) and early first reproduction events (ca. 2 years) with full reproduction capacity (ca. five years) are all characteristic ecological features of C. albidus (Roy and Sonié 1992;De Luis et al. 2008). Climate data were collected from weather stations situated 50 and 450 m from plants of the two habitats, respectively. ...
Background: Population structure and dynamics in natural ecosystems can be affected by seed viability and dormancy. However, how the endogenous contents of phytohormones and vitamin E in seeds relative to the environment affect viability and dormancy is not yet fully understood.
Aims: We studied seed viability and germination capacity in two populations of the Mediterranean shrub, C. albidus exposed to contrasting environmental conditions.
Methods: We measured seed viability and germination capacity, and endogenous contents of ABA, gibberellins and vitamin E in seeds collected from two populations, in two environmentally contrasting environments in north-eastern Spain.
Results: Plants growing in the natural site produced seeds with lower germination percentage but similar viability, indicating higher seed dormancy. Enhanced seed dormancy was paralleled with higher contents of ABA and lower levels of gibberellins. Contents of tocopherols and tocotrienols were higher in seeds of the natural population. Alfa-tocopherol contents in seeds correlated positively with the ratio living:total aerial biomass.
Conclusions: Two Mediterranean populations of C. albidus growing in two sites with contrasting environmental conditions showed marked differences in seed dormancy and germination, which may be explained, at least in part, by differences in seed hormonal contents.
... By germinating under drier conditions, seedlings from seeds with low base water potential are exposed to higher risks, since subsequent dry conditions or droughts might kill them (Daws et al., 2008;Mollard and Naeth, 2015). However, earlier germinating seedlings might also have higher fitness (Luis et al., 2008), because they produce more offspring and are larger or have higher survival rates at the end of the first growing season. Larger seeds are known to generate seedlings with higher survival rates in dry environments (Leishman and Westoby, 1994) and are even known to be associated with drier environment in local moisture gradients (Baker, 1972). ...
Understanding how plant traits interact with climate to determine plant niches is decisive for predicting climate change impacts. While lifespan and seed size modify the importance of germination timing, germination traits such as base temperature and base water potential directly translate climatic conditions into germination timing, impacting performance in later life stages. Yet we do not know how base temperature, base water potential, seed mass, lifespan and climate are related. We tested the relationships between base temperature and base water potential for germination, seed size and lifespan while controlling for bioclimatic regions. We also quantified the phylogenetic signal in germination traits and seed size using Pagel's λ. We used a worldwide data set of germination responses to temperature and moisture, seed size and lifespan of 240 seed plants from 49 families. Both germination temperature and moisture are negatively related to seed size. Annual plants show a negative relation between seed size and base water potential, whereas perennials display a negative relation between base temperature and seed mass. Pagel's λ highlighted the slow evolution of base temperature for germination, comparable to seed mass while base water potential was revealed to be labile. In the future, base water potential and seed mass can be used when moisture niches of plants are to be predicted. Lifespan, seed size and base temperature should be taken into account when analysing thermal limits of species distributions.
... Fast seedling emergence provides the opportunity for seedlings to absorb available nutrients quickly and to become more resilient to subsequent harsh environmental conditions. This was observed for four physically dormant Cistaceae and Fabaceae species from a Mediterranean gorse community, where early emergence resulted in higher fitness than late emergence, with differences remaining significant for at least nine years post-fire ( De Luis et al. 2008). One of the most striking results from our study was that differences in seedling performance between low and high-threshold seeds were only produced under the competition treatment. ...
The production of morphologically different seeds or fruits by the same individual plant is known as seed hetermorphism. Such variation is expected to be selected for in disturbance-prone environments to allow germination into inherently variable regeneration niches. However, there are few demonstrations that heteromorphic seed characteristics should be favored by selection or how they may be maintained. In fire-prone ecosystems, seed heteromorphism is found in the temperatures needed to break physical dormancy, with seeds responding to high or low temperatures, ensuring emergence under variable fire regime-related soil heating. Because of the relationship between dormancy-breaking temperature thresholds and fire severity, we hypothesize that different post-fire resource conditions have selected for covarying seedling traits, which contribute to maintenance of such heteromorphism. Seeds with low thresholds emerge into competitive conditions, either after low severity fire or in vegetation gaps, and are therefore likely to experience selection for seedling characteristics that make them good competitors. On the other hand, high temperature threshold seeds would emerge into less competitive environments, indicative of stand-clearing high severity fires, and would not experience the same selective forces. We identified high and low threshold seed morphs via dormancy-breaking heat treatments and germination trials for two study species and compared seed weight and other morphological characteristics between morphs. We then grew seedlings from the two different morphs, with and without competition, and measured growth and biomass allocation as indicators of seedling performance. Seedlings from low threshold seeds of both species performed better than their high threshold counterparts, growing more quickly under competitive conditions, confirming that different performance can result from this seed characteristic. Seed weight or appearance did not differ between morphs, indicating that dormancy-breaking temperature threshold variation is a form of cryptic heteromorphism. The potential shown for the selective influence of different post-fire environmental conditions on seedling performance provides evidence of a mechanism for the maintenance of heteromorphic variation in dormancy-breaking temperature thresholds. This article is protected by copyright. All rights reserved.
... Fire temporarily produces a competitor-free environment, where success is often contingent on being the first to germinate, establish and develop. It has been argued that species adapted to fire should reduce variability in the timing of germination, such that they would germinate as early as possible in order to increase fitness (Verd u & Traveset 2005;De Luis et al. 2008). We found, however, that germination was tightly related to low water stress, notably after seeds were exposed to fire cues. ...
Mediterranean shrublands are generally water-limited and fire-driven ecosystems. Seed-based post-fire regeneration may be affected by varying rainfall patterns, depending on species' sensitivity to germinate under water stress. In our study, we considered the germination response to water stress in four species from multiple sites across the Mediterranean Basin. Seeds of species with hard-coated (Cistus monspeliensis, C. salviifolius [Cistaceae], Calicotome villosa [Fabaceae]) or soft-coated (Erica arborea [Ericaceae]) seeds, which were exposed or otherwise to a heat shock and smoke (fire cues), were made to germinate under water stress. Final germination percentage, germination speed and viability of seeds were recorded. Germination was modelled using hydrotime analysis and correlated to the water-balance characteristics of seed provenance. Water stress was found to decrease final germination in the three hard-seeded species, as well as reduce germination speed. Moreover, an interaction between fire cues and water stress was found, whereby fire cues increased the sensitivity to water stress. Seed viability after germination under water stress also declined in two hard-seeded species. Conversely, E. arborea showed little sensitivity to water stress, independent of fire cues. Germination responses varied amongst populations of all species, and hydrotime parameters were not correlated to site water-balance, except in E. arborea, when not exposed to fire cues. In conclusion, the species studied differed in germination sensitivity to water stress; furthermore, fire cues increased this sensitivity in the three hard-seeded species, but not in E. arborea. Moreover, populations within species consistently differed amongst themselves, but these differences could only be related to the provenance locality in E. arborea in seeds not exposed to fire cues. This article is protected by copyright. All rights reserved.
... Fire temporarily produces a competitor-free environment, where success is often contingent on being the first to germinate , establish and develop. It has been argued that species adapted to fire should reduce variability in the timing of germination , such that they would germinate as early as possible in order to increase fitness (Verd u & Traveset 2005; De Luis et al. 2008). We found, however, that germination was tightly related to low water stress, notably after seeds were exposed to fire cues. ...
High germination percentage after fires is usually thought to result from heat scarification or dispersal of seeds. Foliage removal by fire causes changes in light quality and soil temperature fluctuations. Here we show that a change in light quality enhances germination of the fire-promoted species Sarcopoterium spinosum L.: A change in the red to far-red ratio from 0.3 to 1.1 increases the germination percentage ten-fold. The seeds do not have a red light requirement but are inhibited by far-red radiation. Germination of S. spinosum was not enhanced by heat nor by an increase in temperature fluctuations.
... Fire temporarily produces a competitor-free environment, where success is often contingent on being the first to germinate, establish and develop. It has been argued that species adapted to fire should reduce variability in the timing of germination, such that they would germinate as early as possible in order to increase fitness (Verd u & Traveset 2005;De Luis et al. 2008). We found, however, that germination was tightly related to low water stress, notably after seeds were exposed to fire cues. ...
... Passage through frugivore gut could change the seed germination rate 46,47 . Seed germination time is related to the fate of seedling establishment and survival 48 ; early germination generally enhances competition and plant fitness 49,50 . In this study, the SGT and MGT of seeds after gut passage (SFD and SID) were lower than those of SFF and SIF, regardless of the other storage conditions. ...
Plant-frugivore mutualism serves an important function in multiple ecological processes. Although previous studies have highlighted the effect of frugivore gut passage on fresh seed germinability, no study has investigated the effect on seed storage after frugivore gut passage. We used the endangered plant, Euryodendron excelsum, to determine the combined effects of frugivore gut passage and storage conditions on the germination percentage and rate of seeds. In particular, three treatments that included storage periods, storage methods, and seed types were designed in the experiment. We hypothesized that seeds that passed through the gut will exhibit enhanced germination capacity and rate during storage. Results showed that the final germination percentage decreased in seeds that passed through the gut, whereas the germination rate increased during seed storage. Germination decreased in most types of seeds under both dry and wet storage after 6 months compared with storage after 1 and 3 months. The results suggest that after frugivore gut passage, E. excelsum seeds cannot form persistent soil seed bank in the field, and were not suitable for species germplasm storage. These finding underscore that seeds that passed through frugivore gut have long-term impact on their viability and germination performance.
... Therefore, increased germination speed in pioneers may improve recruitment (Jacomassa & Pizo 2010) if early growing seedlings succeed during the intense intraspecific competition that follows germination (Weaver & Cavers 1979). Additionally, reduced germination time may be advantageous in fire-prone habitats (de Luis et al. 2008) such as the Cerrado. In this case, early germinants may have increased chances of growing and reproducing after a major disturbance, such as fire. ...
Background and aims - Frugivory and seed dispersal are of major importance for plant recruitment and distribution. However, few studies have addressed the effects of gut passage on seed germination in complex fruit-frugivore systems involving multiple species. Here, we examined whether gut passage by seven bird species affects seed germination of eight Melastomataceae species from the Brazilian Cerrado, a Neotropical savanna.
Methods – We take advantage of the generalist dispersal system of melastomes in order to compare the dispersal quality among bird species by contrasting seed germination of hand-cleaned, gut-passed seeds and seeds within intact fruits. We studied gut passage effects on seed germination percentage and mean germination time (MGT) of Clidemia urceolata and seven Miconia species.
Key results – Less than 4% germinability was observed for seeds within intact fruits across all plant species, indicating that seed cleaning is required prior to germination. The action of guts on the seeds had non-significant or minor additive effects on germinability compared to hand-cleaned seeds depending on the plant species. Gut treatment had no effect on MGT of two species and minor effects on other three species. However, mechanical/chemical effect significantly decreased MGT of C. urceolata and M. albicans while it increased MGT of M. ibaguensis. There were significant species-dependent effects depending on both bird and plant species, suggesting that specie-specific outcomes arise from Neotropical fruit-frugivore interactions in plants with generalist dispersal systems.
Conclusions – Germination enhancement deriving from gut scarification was not observed for all species, but seed cleaning seems to be an important benefit provided by frugivores to Cerrado melastomes. The variable outcomes resulting from complex fruit-frugivore interactions potentially affect the recruitment of Cerrado melastomes.
... days), though the difference was not statistically significant (P = 0.25). This pattern could be expected since early germination in low elevation (the core of vulgaris) may reduce mortality by allowing more time for seedling growth before the onset of the summer stress (De Luis et al. 2008). Similarly, late germination in high elevation (the core of nevadensis) can improve seedling survival by reducing the risk of experiencing late frosts (Giménez-Benavides et al. 2007;Ramírez et al. 2006). ...
Abstract
Aims
Phenotypic plasticity and local adaptation of populations at their distributional limits are crucial to understand species colonization and persistence in novel or marginal environments, as well as species divergence and niche width evolution. We assess the
contribution of these processes to shape current elevational limits and determine elevational phenotypic divergence between two subspecies of Aquilegia vulgaris (subsp. vulgaris and nevadensis).
Methods
We conducted sowing and transplant experiments considering four elevations throughout the current elevational range of Aquilegia vulgaris in southern Iberian Peninsula. Experiments were designed to explore, on the one hand, local adaptation through three components of performance (germination, survival and growth) and, on the other hand, the phenotypic differentiation and/or plasticity associated to local adaptation. Four populations per subspecies (three from the elevational core and one from the elevational boundary) were used as seed sources. Patterns of local adaptation and phenotypic differentiation are examined in the context of the “centre-periphery” hypothesis.
Important Findings
Central populations of both subspecies performed better at their local elevations while marginal populations were maladapted, confirming the hypothesis and contributing to explain the current elevational segregation of these subspecies. Density of glandular pubescence and germination timing seem to be related to local adaptation, through phenotypic differentiation between subspecies or elevations. The widespread subsp. vulgaris showed signals of adaptive plasticity in the timing of germination while it was not the case in the endemic subsp. nevadensis.
In August 2021, very intense fires swept through various forested areas in northern Algeria, particularly in Kabylia. The population dynamics of Cistus salviifolius and Cistus monspeliensis were studied along a post-fire successional gradient during the first nine months (September 2021 – May 2022), in two forest communities: the Cork oak ( Quercus suber ) and the Aleppo pine ( Pinus halepensis ) forests in the coastal zone of Bejaia province. The Cistus spp. germinations were counted monthly in each forest on 10 plots of 1 m ² , evenly distributed along 2 transects of 45 m each. The results showed that the majority of germinations occur in December with 207.5 ± 24.2 seedlings in the Cork oak forest and 171.3 ± 18.0 seedlings in the Aleppo pine forest. Student's t-test does not reveal significant differences for December between the two communities. During the first months following the fire (September and October 2021), germinations were almost absent. The monthly rainfall in September 2021 was estimated at 16.25 mm, an insufficient amount for effective germination. Late germination results in an extension of its period, showed a high rate in January 2022 with 42.2 ± 2.1 and 11.5 ± 0.8 seedlings, respectively, in the Cork oak forest and the pine forest. Beyond January, germination was practically nonexistent in both communities. Therefore, the majority of the seed germination was concentrated in November, December, and January with a unimodal germination pattern.
Predation of cotyledons can reduce short-term survival and growth in emerging oak seedlings, potentially affecting species recruitment. However, the physiological basis of reduced seedling performance after early cotyledon predation and the mid-term consequences of cotyledon predation on seedling drought tolerance remain poorly understood. We performed an experiment where we simulated predation by systematically removing cotyledons from Quercus variabilis seedlings at seven growth stages during emergence in the first growing season. We assessed survival, growth, and nitrogen (N) and non-structural carbohydrate (NSC) storage. Subsequently, in the second growing season, we assessed drought tolerance in seedlings with cotyledons removed at four growth stages in the previous season, and subjected seedlings to two drought levels to assess overall performance. During the first growing season, seedling survival showed less sensitivity to cotyledon removal compared to growth, N and NSC storage, which were significantly reduced when cotyledons were removed within the first 4 days after emergence. Early cotyledon removal (4 days after emergence) in the first growing season enhanced drought tolerance in the second growing season by reducing leaf embolism vulnerability, but it did not affect leaf drought tolerance traits such as the osmotic potential or the modulus of elasticity. Early cotyledon removal had a lasting effect on seedling growth and N and NSC storage building in the second growing season. Additionally, it exacerbated the negative consequences of drought on seedlings growth and N storage building, but it did not influence survival or NSC storage. Our findings evidence that early cotyledon removal in emerging oak seedlings has significant short- and medium-term repercussions on growth and capacity to store N and NSC, and it hinders the capacity of seedlings to respond to drought despite early cotyledon removal increases leaf drought tolerance. These functional legacies can influence oak seedling recruitment.
Background
Species of Mediterranean shrublands regenerate after fires from persistent (PSSB) or transient (TSSB) soil seed banks, which can affect postfire regeneration owing to the different importance of the current seed crop depending on soil seed bank types. However, seed dispersal in these shrublands has been little investigated. Here, we recorded temporal and spatial patterns of seed dispersal in four shrubs with different soil seed banks (persistent soil seed sank, PSSB; transient soil seed bank, TSSB), three of them are seeders (Cistus ladanifer [PSSB], Salvia rosmarinus, [TSSB] and Erica umbellata [PSSB]) and one is a resprouter (Erica arborea [TSSB]) in an old (> 40 year.) shrubland in Central Spain. A 15 x 10 m plot was chosen and divided into a 0.5 x 0.5 m grid, where plant cover and density were measured. At 106 quadrats, seed traps were set and periodically (1–2 monthly) monitored for three years.
Results
S. rosmarinus dispersed in late spring-early summer, E. arborea dispersed during the summer, and C. ladanifer and E. umbellata dispersed since early summer until nearly late spring of the next year. Globally, seeds were being dispersed all year round. Seed crop varied between years although species differed in the year their seed crop was largest, despite large differences in climate. Seed rain and cover of each species were poorly related. Semivariogram analysis showed that seed dispersal expanded beyond the cover of each species a few meters. No association between seed crop size and spatial dependence was ascertained. While species dispersal tended to be negatively related to one another, E. arborea seeds tended to dominate underneath the other species.
Conclusions
Seed dispersal was consistent with the type of soil seed bank and postfire regeneration strategy: S. rosmarinus dispersed before the fire season; C. ladanifer and E. umbellata dispersed mostly after the fire season, which is coherent with a bet-hedging strategy against seed predators; E. arborea dispersed before the rainy season. The dominance of E. arborea seeds underneath the other species suggests that this midsuccessional species might dominate when openings form due to the deaths of the seeders standing plants, which have lower longevity.
The ecological stability of Mediterranean ecosystems is being threatened by climate change. One of the impacts that is expected to be aggravated is the effect of summer drought prolongation toward previous or subsequent seasons by becoming more frequent. This, along with wildfires, could trigger synergistic negative effects on ecosystem regeneration capacity. Here we assessed how extending summer drought in two different ways (to autumn, AutExcl treatment, or bringing it forward to the following spring, SprExcl treatment) would affect plant recovery after an experimental fire carried out in summer in a Mediterranean seeder community. By installing rainout shelters, we assessed differences in seedling emergence, survival and establishment in the main families (Cistaceae, Labiatae, Leguminosae), and the effect on species richness and community composition. We observed that these post-fire dry season extensions reduced the total number of established seedlings and species richness. The most impacting drought treatment was AutExcl. However, the regeneration response was variable depending on the studied family. SprExcl was also determinant for Labiate survival rates. These results suggest that drought events which prolong the usual summer season may have a permanent drought legacy effect on seeder communities as practically all the seeder species populations were established in the first post-fire year. This fact is relevant for Mediterranean ecosystems dominated by seeder species as severer and longer droughts are increasingly recorded and are expected to become more frequent in forthcoming decades.
Large‐scale abortion of immature fruits is a pervasive phenomenon across seed plants due to maternal physiological decisions associated with matching resources with fruit crop size. Aborted fruits are usually disqualified from studies of both fruit production and seed dispersal. However, a considerable number of developing seeds occur within immature aborted fruits. We evaluated the untested hypotheses that seeds within aborted fruits are viable and that incomplete predation of seeds within aborted fruits by hoarding rodents provides, in addition to seed movement, increased germination and seedling emergence. To this end, we studied the system composed by the Iberian pear Pyrus bourgaeana and several rodent species in Mediterranean Spain. About a third of aborted fruits found beneath tree canopies (n = 2430) were partially eaten by rodents. Using a seed sowing experiment, we revealed that a considerable fraction of seeds from P. bourgaeana aborted fruits are viable, germinating, and emerging seedlings. Paradoxically, however, these seeds are de facto unviable since they are confined within the extremely hard pericarp of aborted fruits, which prevents any seedling emergence and thus any contribution to tree recruitment. We show that only when rodents partially gnaw the pericarp walls of aborted fruits, seeds that escaped from predation have the prospect of emerging and thus potentially contributing to tree regeneration. Thus, in this and probably in many other similar synzoochore systems, rodents act as rescuers of seeds confined within aborted fruits, conferring the plants a largely overlooked benefit that could shape the reproductive strategy of many plant species.
Wildfires trigger changes in vegetation dynamics if the existing community does not resist the fire and succumbs. However, the same vegetation state may still occur if populations show post-fire resilience, that is, if they are able to regenerate after fire. Such regeneration will be a function of interactions between propagule availability (aerial or soil seed banks or other seed sources nearby), its establishment success (dependent on soil resources, dormancy break, herbivores, and microsite conditions), fire recurrence, and mycorrhizal networks. When pre-fire species fail to survive and regenerate after the fire, changes in the vegetation state may lead to either a forested or a deforested state, depending on legacies from the previously established community, climatic conditions and water balance, and other processes. Climate change may compromise post-fire state changes when newly established communities cannot survive under the novel environmental conditions expected for the end of this century. Here we review overall post-fire vegetation changes, with a particular emphasis on Mediterranean environments.
Fire has been present on Earth since vascular plant expansion over land at the turn of the Devonian, 420 mya. It is thus to be expected that wildfires have shaped physiological plant traits. The question is which traits have evolved under fire activity and to which extent. Here we present the general hypothesis that plants have evolved bet hedging strategies, whenever possible, to jointly deal with the multiple stresses and disturbances they face during their evolutionary lifetimes. We also note that, in some instances, trade-offs in the adaptations to stress and disturbance have also developed. The traits that are most likely to have evolved in response to fire are related to post-fire recruitment and persistence. We argue that the evolution of these traits has also been shaped by drought and other environmental factors. We also discuss the evidence on whether plant traits that enhance flammability could have evolved in response to fire, but we find more plausible the explanation that plant traits affecting fire behavior emerge from plant responses to other environmental factors.
Islands are well-known to house an incredible biodiversity, higher level of threatened species and extinctions than mainlands. Because of human activities and climate change, these endangered regions required advanced conservation and restoration strategies.
In this study, we investigated seed germination ecology of four native Malvaceae species (Dombeya acutangula, Dombeya populnea, Ruizia cordata and Thespesia populneoides) of degraded dry lowlands of Reunion Island. We measured seed imbibition, investigated the dormancy class of seeds, determined light requirements for germination and identified treatments to improve germination of these species. For this purpose, germination tests were performed over 32 days and two photoperiods (12 h/12 h or 0 h/24 h), by using seeds treated with H2O2, gibberellic acid and smoke water. Mechanical and chemical scarifications as well as heat treatment were also carried out. Germination percentages were analyzed by fitting generalized linear models (GLMs) with a logit link function.
For the four species, a significant mass increase is detected for scarified seeds after a week imbibition (>60% mass increase). Germination percentages of seeds treated with H2O2, GA3 and smoke water were not significantly different from control seed. On the contrary, scarified seeds exhibited significantly higher germination percentages than control seeds. In addition, germination speed was also significantly higher for scarified seeds. These results are congruent with a physical dormancy phenomenon of seeds of the four Malvaceae shrubs. In addition, no particular light requirement was observed for germination. Artificial methods to break dormancy and stimulate germination described in this study could improve establishment success in arid habitats.
Key message
The rapid production of a large, deep root system during seedling establishment is critical for pines to colonize dry Mediterranean locations.
Abstract
Root properties can influence plant drought resistance, and consequently plant species distribution. Root structure strongly varies across biomes partly as a result of phylogeny. However, whether the spatial distribution of phylogenetically close plant species is linked to differences in root properties remains unclear. We examined whether root properties mediate the strong correlation between summer drought intensity and the spatial segregation of pine species native to southern Europe. For this, we compared the seedling root growth and structure of five ecologically distinct pine species grown in 360 L rhizotrons for 19 months under typical hot and dry Mediterranean conditions. We studied the mountain and boreo-alpine pines Pinus sylvestris and Pinus nigra, and the Mediterranean pines Pinus pinaster, Pinus pinea, and Pinus halepensis. Mediterranean pines formed deep roots faster than mountain pines, their shoots and roots grew faster and had higher root growth, especially P. halepensis, at low air temperature. By the end of the study, Mediterranean pines had larger root systems than mountain pines. Neither distribution of root mass with depth nor root-to-shoot mass ratio varied significantly among species. Across species, minimal annual rainfall to which species are exposed in their range related negatively to root growth but positively to specific root length and the time needed for roots to reach a depth of 40 cm. This study highlights the importance of root growth as a driver of pine distribution in southern Europe and suggests that rapidly producing a large, deep root system may be a key attribute for pines to colonize dry Mediterranean locations.
In degraded dryland systems, native plant community re‐establishment following disturbance is almost exclusively carried out using seeds, but these efforts commonly fail. Much of this failure can be attributed to the limited understanding of seed dormancy and germination traits.
We undertook a systematic classification of seed dormancy of 26 species of annual and perennial forbs and shrubs that represent key, dominant genera used in restoration of the Great Basin ecosystem in the western United States. We examined germination across a wide thermal profile to depict species‐specific characteristics and assessed the potential of gibberellic acid (GA3) and karrikinolide (KAR1) to expand the thermal germination envelope of fresh seeds.
Of the tested species, 81% produce seeds that are dormant at maturity. The largest proportion (62%) exhibited physiological (PD), followed by physical (PY, 8%), combinational (PY+PD, 8%), and morphophysiological (MPD, 4%) dormancy classes. The effects of chemical stimulants were temperature‐ and species‐mediated. In general, mean germination across the thermal profile was improved by GA3 and KAR1 for 11 and five species, respectively. We detected a strong germination response to temperature in freshly collected seeds of 20 species. Temperatures below 10°C limited the germination of all except Agoseris heterophylla, suggesting that in their dormant state, the majority of these species are thermally restricted.
Our findings demonstrate the utility of dormancy classification as a foundation for understanding the critical regenerative traits in these ecologically important species and highlight their importance in restoration planning.
This article is protected by copyright. All rights reserved.
Priority effects are hypothesized to play an important role in community assembly and may promote suppression of native by exotic species. Work in a range of grassland systems has proved valuable for testing these effects, demonstrating that earlier germination by some exotic annual grasses contributes to their competitive dominance over natives. Yet few studies have measured native forb germination phenology under field conditions, and the demographic consequences of emergence timing for competitive interactions and native fitness are not well understood. We focused on three native annual species in a southern California grassland dominated by exotic Bromus spp. over three years, measuring (1) seedling emergence rates, for both early (October) and later (November and December) germinators; (2) effects of exotic grasses on native survival and reproduction, through a grass removal experiment; and (3) interactions between emergence timing and grass competitive effects on native mortality, survival, and flowering. We quantified tradeoffs of emergence timing, by estimating mortality experienced by early germinants until the late cohort emerged (early survival), and then for both cohorts from the time of late emergence to flowering (spring survival). The two most common focal natives, Amsinckia intermedia and Phacelia distans, varied substantially in germination phenology but primarily emerged early. The less abundant Clarkia purpurea germinated late. Late emergence reduced spring survival in control plots but not those where exotic grasses were reduced experimentally, supporting the importance of priority effects and benefits of early germination in competition with grasses. However, early emergence entailed a high cost of initial mortality risk in some years. We found no effect of emergence timing on size at flowering. Estimates of net survivorship to flowering suggest that late emergence consistently was associated with the highest survival when exotic grasses were reduced experimentally. Early emergence was more favored in control than in exotic grass reduction plots, but the survival tradeoffs differed substantially between years. These results suggest that priority effects contribute to suppression of native forbs, but may not consistently promote higher fitness for earlier germinators. Instead, exotic invasion may increase yearly variation in the fitness consequences of native germination phenology, with potential implications for bet hedging strategies.
Cold temperature seed germination and rapid root growth influence the ability of native plants to establish in the presence of invasive winter annuals. This represents a potential problem for plant material selection in the face of climate change. If seeds sourced from cold winter climates germinate and grow rapidly early in the season, managers that select materials from warmer winter climates could miss populations with traits that promote competitive establishment at restoration sites. We examined seed germination timing and seedling growth rates of the exotic grass, Bromus tectorum, two wild-collected Poa secunda accessions, and four commercial P. secunda accessions under two temperature regimes (20°C day/15°C night and 10°C day/5°C night) to examine the mechanisms responsible for differences in establishment and survivorship between P. secunda accessions observed in a previous field study. Our results show that B. tectorum had earlier germination, faster root elongation, and greater total root growth than all P. secunda accessions in both temperature regimes. Wild-collected P. secunda accessions germinated later and had slower cold temperature growth rates than most commercial accessions. Poa secunda accessions sourced from areas with colder winter climates germinated earlier and had greater total root length in the cold temperature treatment, suggesting that source location climate can be used to select plant materials with traits beneficial for seedling establishment and tolerance of invasive winter annuals.
Contribution des Légumineuses à la régénération après feu des forêts de Quercus suber et Pinus halepensis du Nord-Est Algérien.
Le rôle des Légumineuses dans la régénération après feu a été largement étudié sur la rive nord de la Méditerranée, mais aucune donnée n’est disponible concernant la rive sud. Le but de cet article est d’analyser la dynamique des Légumineuses dans une subéraie et une pinède à Pin d’Alep du Nord-Est Algérien durant les premiers mois après un feu de faible intensité. Les aspects de la démographie des germinations des Légumineuses, leur contribution à la biomasse totale et la richesse spécifique sont considérés. Les deux communautés ne présentent pas de différences majeures. Toutes deux montrent des modèles démographiques similaires : les germinations de Légumineuses commencent à émerger très tôt (novembre) après le feu (octobre) et continuent à s’établir abondamment avec un premier pic en décembre et un deuxième en mars, avec un ralentissement significatif en janvier et février. La germination diminue à partir d’avril pour atteindre son minimum en mai et complètement s’arrêter en début juin. Ce modèle en deux pics plutôt qu’un seul, comme déjà rapporté, serait vraisemblablement dû au froid exceptionnel durant janvier et février 2005 (neige jusqu’au niveau de la mer) d’où un ralentissement de la germination et son décalage à mars. Huit mois après l’incendie (vers la fin juin, période où la végétation herbacée commence à sécher), la biomasse aérienne des Légumineuses affiche un maximum de 37,8 ± 1,83 g/ m2 dans la subéraie et 26,7 ± 1,63 g/ m2 dans la pinède. Sept mois après le feu, relativement aux autres familles de plantes, les Légumineuses sont floristiquement bien représentées avec 19,8 ± 1,11 % des espèces dans la subéraie et 24,3 ± 2,05 % dans la pinède, valeurs nettement supérieures à celles rapportées pour d’autres écosystèmes de type méditerranéen (3,8 -13,3 %), probablement en raison de la localisation géographique (basse latitude) de notre aire d’étude et la pression de surpâturage qui favorise l’installation des Légumineuses.
Postfire revegetation with native perennial grasses is difficult to achieve in disturbed arid rangelands. If local populations are adapted to current conditions, then locally collected seed would be predicted to have higher survival than nonlocal seed, and using local seed should improve revegetation success. However, for revegetation projects in the Great Basin, sufficient quantity of local seed is often difficult to obtain commercially, so seeds often originate from source populations that are hundreds of kilometers from the project site. We investigated whether seed source affected first-year establishinent of big squirreltail (Elymus multisetus M.E. Jones) seedlings in a common garden field trial 50 km north of Reno, Nevada. For the trial, we used wild, locally collected seed and commercially produced seed originating from Oregon, Idaho, and California. Several phenological and growth traits varied significantly between source populations. Eighty-six percent of local seeds emerged, compared to 71%, 61%, and 12% of seeds from Idaho, Oregon, and California, respectively. Local seeds emerged, on average, 9 days earlier than seeds from other sources. Fourteen percent of the local seedlings survived through the first year, exceeding survival by Oregon (12%), Idaho (8%), and California (2%) seedlings. Though survivorship was highest for local seed, local seedlings were smaller, producing 24% fewer leaves than the most productive seedlings from the Idaho seed source. Our data suggest that seed source is an important factor in seedling establishment. If local seed can survive significantly better than regionally collected, commercially produced seed, it may be both ecologically and economically beneficial to use local seed in revegetation.
In three Mediterranean old fields, one, seven, and fifteen years after the last ploughing, small scale disturbances (0.25 m2) by contact herbicide associated or not with litter removal and scratching of the top 3 cm of the soil were generated in October 1988, December 1988, and March 1989. Subsequent changes in cover, species richness and composition were observed over the two following vegetation cycles (until May 1990), and compared to the dynamics in undisturbed samples. The identity of the colonizers for each disturbance date were compared to the soil readily-germinable seed content, sampled simultaneously to the disturbances. The species richness of the samples within the fields increased the first year after disturbance. Within-field heterogeneity for taxonomic composition was unchanged, but species turnover was increased by disturbances. The dynamics of richness and composition followed consistent patterns in the three fields. These patterns were strongly related to the seasonal rainfall distribution and clearly linked to the germination timings of the species and to seed bank composition. The identity of species depending on season and treatment were independent between fields. The effects of small scale disturbances on patterns of species establishments and replacements depended on their timings. Disrupting the dominance by autumn established grasses and legumes, they opened windows for germinations of annual forbs and for spring establishment of perennials. These species were otherwise present as understory species or in the seed bank. Results of these experiments provide insights into the mechanisms of maintenance of species diversity in this Mediterranean old field system. Asynchronous small-scale disturbances appear to be effective in maintaining diversity as a result from the interplay of differences in regeneration niches, lottery for establishment, and the incidence of different conditions in time and space.
An examination of 203 seed lots from 42 Old World species (or 54 taxa), with representatives from all five genera (Cistus, Fumana, Halimium, Helianthemum, and Tuberaria) and an additional seed lot of the New World Lechea maritima shows that the phenomenon of hardseededness is a prominent characteristic of the entire Cistaceae family. Promotion of seed germination in the laboratory can be obtained by mechanical scarification and thermal pretreatment, while light seems to be totally ineffective. A seed ecology syndrome for Cistaceae is postulated, featuring small seed size, hardcoatedness (primary dormancy), short-distance dispersal, long-term persistence in soil seed banks, fire- or heat- induced seed “softening”, an opportunistic strategy of germination (germination at a wide range of temperature and light conditions), and a slow germination rate of “softened” seeds. This syndrome is suggested to endow Cistaceae, a principally Mediterranean family, with a considerable ecological advantage in the summer-dry and fire-prone Mediterranean climatic conditions.
This is the second edition of a multi-author book first published in 1992. It deals with all aspects of plant regeneration by seeds, including reproductive allocation, seed dispersal and predation, longevity, dormancy and germination. All chapters have been updated, and four new chapters added on seed size, seedling establishment, the role of gaps, and regeneration from seed after fire.
The time at which a seedling emerges can determine its future success as a plant. Despite the large number of studies that have examined the effect of emergence time on different components of plant fitness (survival, growth, and/or fecundity), the potential evolutionary response to selection on seedling emergence date is still poorly known. In this study, we review 55 of those studies by a random-effects meta-analysis, considering the phylogenetic relatedness among taxa. We test the following hypotheses: (1) early emer- gence increases seedling survival, growth, and fecundity, (2) early emergence is more advantageous to large-seeded species than to small-seeded ones, as the former can com- pensate for the lower number of seeds by increasing seedling survival, (3) perennial plants benefit more than annuals from early emergence, as the iteroparity of the former allows them to risk seedling emergence to the best conditions each year, whereas the semelparity of the latter forces them to spread the risk of emergence over time, and (4) the effect of emergence time may depend upon the experimental conditions (field vs. controlled exper- iments in a greenhouse or laboratory). Our results show that early emergence differentially affects components of plant fitness, with no effect on seedling survival but large benefits to seedling growth and fecundity. Such effects vary depending upon intrinsic factors like seed size or life-form, and also upon methodology (census time and experimental condi- tions). Large-seeded species gain from emerging early by growing more during their first growing seasons, although they survive and reproduce similarly to small-seeded species. The survival benefit of early emergence is greater in perennial than in annual species, thus supporting hypothesis 3. The relationship between emergence time and seedling growth appears to be stronger under controlled conditions than in the field, probably as a result of the unlimited nutrient and water resources of the former. In field conditions, in contrast, limited resources probably decelerate the growth of early seedlings, precluding the detection of differences between these and late seedlings.
Mediterranean climate ecosystems of the Mediterranean rim are rich in legumes, both as woody shrubs of the late successional stages and as short-lived, pioneer herbaceous plants. In a survey of the floras of numerous geographic regions of Greece, legumes in Mediterranean parts are found to contribute considerably more (11-16% of the total number of species) than in non-Mediterranean regions (6-8%). Legume presence is also notable in other Mediterranean-type ecosystems of the world; nevertheless most leguminous taxa of the Mediterranean basin are herbs in contrast to a significant contribution of shrubs in California and Chile. Due to their long-lived soil banks of hard coated seeds herbaceous legumes are usually among the early post-fire colonizers in the Mediterranean and may play a significant role in the succession of fire-prone communities.
Since the early 1990s, Mediterranean gorse shrublands have expanded significantly in the Mediterranean regions of Spain mainly as a result of the increase in the frequency and extension of forest fires. Mediterranean gorse (Ulex parviflorus), which has been described as a degradation stage of forest communities after fire, has also been described as a fire-prone community. Thus, its presence increases the risk that new fires might occur. In spite of this evidence, there is little information on both the composition and structural characteristics of these communities or the relationship that might exist between these vegetation characteristics and fire behaviour. In this paper we present the results of a characterization of the vegetative structure (plant density, specific composi- tion, biomass fractions, and horizontal and vertical fuel distribution) in Mediterranean gorse. We also analyse fire behaviour using indicators obtained at different scales. Our results show mature Mediterranean gorse shrublands to be communities with high biomass values (3000-4000 g m−2) and high horizontal and vertical vegetation con- tinuity, in which the proportion of fine dead fuel fractions with low moisture content is around 50% of the total phytomass present. Ulex parviflorus is the dominant species and its degree of dominance is a key element in the behaviour of fire. Both the fire-line intensity values and the fire severity values observed can be considered high with respect to those observed in other Mediterranean communities, thus confirming Mediterranean gorse as a high-risk community.
Black ash circles are found under the burned canopies of big dead pine trees up to three years after fires. Similar circles are formed as the result of a spatial pattern of seedling recruitment after fires. It has been suggested that the accumulation of ash around the burned trees, and the differential reaction of seed germination to ash, may be a major cause for the spatial pattern of seedling recruitment after fires. The results of germination experiments in pots prove that thick cover of ash has a negative effect on germination of Pinus halepensis Miller, and on germination and growth of Cistus salviifolius L. Ash solutions in petri dishes had no effect on germination and growth of both species. Pinus seems to be more well adapted than Cistus to germination and growth in sites with high amounts of ash after fire. Our results support the hypothesis that the ash around the burned pine trees, and the differential reaction of plant species to the ash may explain the spatial pattern of seedling recruitment after fire. We suggest that the relatively high resistance of pine seed germination to osmotic stress is an adaptation to post fire germination rather than to germination in arid zones.
The impact of fire on the viability of the entire soil seed bank in a Mediterranean pasture dominated by weeds originating from arable fields, and its recovery in the first post-fire year, were investigated. Soil samples were excavated separately in 0-2 cm and 2-5 cm deep layers, and their seed content was assessed using the seedling emergence method. Emergent seedling counts were carried out in the field during the spring following the fire. Analysis of samples from an unburnt stand revealed that annuals (83% species, 86% seeds). and weeds (50% species, 30% seeds) were a major component in the seed bank. Seed banks of most species (85%) were accumulated in the upper soil layer. Denoting their transient nature. Fire severely reduced the density and species richness of the seed bank, as expected for a mainly transient soil seed bank in a community not exposed to a recurrent wildfire regime throughout its evolutionary history. One year after the fire, the seed bank increased in density and species richness, particularly in the upper soil layer. The recovery occurred in two ways: i) in-site seed production from seeds which survived the fire and germinated. and ii) wind-borne seed invasion from adjacent unburnt vegetation. The first type of recovery was mainly the result of relatively large-seeded species with short-distance seed dispersal mechanisms, whereas the second was observed for anemochorous and/or tiny-seeded species. We conclude that the ability of weedy communities to respond to fire is based on the colonizing and invasive nature of the species. Consequences for the use of fire in the management of such communities are discussed.
The evolution of intrinsic growth rate has received,ed less attention than other life history traits, and has been Studied differently in plants, homoiotherms, and poikilotherms. The benefits of rapid growth an obvious, so the problem is to explain the costs and tradeoffs that cause organisms to grow below their physiological maximum. Four prevailing themes emerge from the literature: (1) slow growth is adaptive for dealing with nutrient stress, (2) the tradeoff between growth rate and development limits growth in species that require mature function early in life, (3) rapid growth evolves when a minimum size must be reached quickly, such as for sexual maturation or over wintering and (4) rapid growth may evolve to compensate for slowed growth owing to environmental conditions. Evidence for each of these themes is detailed for plants, homoiotherms, and poikilotherms. In addition, empirical evidence is reviewed costs of rapid gr growth, including increased fluctuating asymmetry, reduced immune capacity, and reduced ability to respond to environmental stress.
We documented patterns of surface heating associated with chaparral fire to characterize funda-mental scale variation in the intensity of this stand-replacing disturbance. To test how this variation may influence community structure, we studied its effect on the soil seed bank and the distribution of seedlings and resprouts that emerged after fire. To evaluate the long-term significance of initial patterns, we monitored vegetation development for 4–5 yr, thereby encompassing the dynamic portion of the chaparral fire cycle. We studied two stands on level uniform terrain before, during, and after fall fires. Stands were dominated by chamise (Adenostoma fasciculatum), a postfire seeder/sprouter. Nonsprouting Arctostaphylos and Ceanothus spp. were also present. Preburn vegetation, seed populations, soil heating, and postburn plant growth were analyzed along transects of contiguous 1-m 2 plots, so that we could block them together incrementally to identify scale dependence of patterns. In addition, we directly compared heating effects under the fuel array with those just outside by establishing plots in canopy gaps, under the adjacent canopy, and in gaps created and eliminated by reciprocally translocating fuel. Pre-and postburn seed populations were estimated in soil samples collected from all plots. The proportion of seed that survived above and below 2.5 cm in the soil was determined in a subset of plots. The amount and distribution of canopy fuel that collapsed during fire and smoldered on the ground caused pronounced spatial variation in total surface heating. The strength of relationships among patterns of soil heating, preburn canopy, surviving seeds, and seedlings and herbaceous resprouts was consistently most pronounced in blocks 3–5 m long. At this scale, postburn patterns were strongly negatively associated with the amount of preburn canopy and the pattern of soil heating this fuel created. Seedlings or herbaceous resprouts of numerous species were abundant where soil heating was relatively low, most notably in natural and created canopy gaps. Conversely, areas where dense canopy occurred before fire, especially gaps displaced by fuel addition, were barren except for occasional Arctostaphylos and Ceanothus seedlings. These obligate postfire seeders, along with the subshrub Helianthemum scoparium, had more deeply buried seeds, and some of them were able to survive where soil heating was prolonged. However, Helianthemum did not emerge from depth. Seedlings of Arctostaphylos and Ceanothus nearest Adenostoma burls survived significantly better when Adenostoma failed to resprout. This was common in one burn where heating was relatively high and burl size was small. Seed mortality prevented Adenostoma seedling emergence from occurring where its seeds were most abundant prior to fire, which was in proximity to its burls. Adenostoma seedlings did emerge in areas of lower soil heating, but their survival was inversely related to the density of Helianthemum seedlings. No shrub seedlings emerged after the first year following fire because their seed banks were exhausted by fire-induced mortality and/or germination. After 4–5 yr, few young Adenostoma remained. The combination of seedling and resprout regen-eration allowed this shrub to maintain dominance, but to a lesser extent in the older stand. Our results support a vegetation pattern–process model in which local species distributions after fire in Adenostoma chaparral are antecedently linked to the physical and chemical properties of the canopy. These control the nature of combustion, the soil heating that results, and the distribution of seeds and resprout tissues that survive. The vegetation develops entirely from these sources, so fire-induced patterns are manifest in the long-term structure of this vegetation.
Many studies recognize that growth carries with it a mortality risk that can influence an animal's growth rate.
Data suggest that these costs of growth act over a range of time‐scales, from instantaneous to an animal's lifetime.
Models of adaptive growth rate have not addressed the issue of differing time‐scales over which the costs of growth act. Here, we develop an adaptive growth model in which the costs of growth are delayed for a period of time, to assess optimal growth strategies in relation to delays in growth costs.
The optimal growth rates are calculated assuming one of two possible fitness measures: the reproductive rate, R 0 and the intrinsic population growth rate, r .
It is shown that if the costs of growth are felt only after maturity, then growth compensation can be an adaptive strategy, even in an unchanging environment.
Compensatory growth is predicted only when R 0 is the relevant fitness measure, implying that this mechanism of compensatory growth is sensitive to the processes of population regulation.
The effect of time‐delayed costs for other life‐history problems is discussed in light of these results.
Large‐seeded species have long been known to have higher survivorship during establishment than small‐seeded species. Here, we assessed the size of this advantage by compiling published data on survival through seedling emergence, seedling establishment and sapling establishment.
We found no relationship between seed mass and survival through the transition from viable seed in or on the soil to newly emerged seedlings ( P = 0.47, n = 33 species).
Synthesis of data from experimental studies on the advantages of large‐seeded species establishing under particular hazards (such as shade, drought or herbivory) confirmed that seedlings of large‐seeded species perform better than those of small‐seeded species in most situations. However, the magnitude of this advantage was not sufficient to counterbalance the greater number of seeds produced by small‐seeded species m ⁻² of canopy outline year ⁻¹ .
Synthesis of data from field studies of populations under natural conditions also showed that large‐seeded species have higher survival through early seedling establishment than small‐seeded species ( P = 0.006, n = 112 species). However, the magnitude of this advantage would only be sufficient to counterbalance the greater number of seeds produced by small‐seeded species m ⁻² of canopy outline year ⁻¹ if mortality continued at the same rate for some time.
The time required for a species with 10‐fold larger seeds to recoup the advantage gained by a smaller‐seeded species during seed production ranged from 8.8 weeks for the smallest seeded species in the data set, up to an implausible 4.2 years for the largest‐seeded species. Thus, while large‐seeded species do have a survival advantage over small‐seeded species during seedling establishment, the available evidence suggests that advantages must also accrue during other stages in the life cycle. One possibility is that the greater seed production of small‐seeded species (m ⁻² of canopy outline year ⁻¹ ) is partly offset by larger canopies and longer reproductive life spans in large‐seeded species.
Dormancy in the hard seed coats of Mediterranean species is considered a strategy that enables persistent seed banks to be
formed in the soil. An important factor related to seed coat fracture and dormancy breakage in Mediterranean ecosystems is
heat. Nevertheless, the effect of factors other than heat on dormancy breakage in these species has hardly been studied. To
investigate the different ecological factors involved in germination, in the laboratory we applied several scarification treatments
to seeds with chromatic polymorphism. We evaluated the effect of soil seed depth during experimental burns by sowing seeds
at −1, −3 and −5cm in the soil profile, and we also studied the effect of seed origin on the posterior germination of seeds
from 4 and 10year-old shrubs as well as from the soil seed bank. U. parviflorus shows clear chromatic polymorphism: its brown seeds present higher dormancy levels than its yellow seeds. The different techniques
of dormancy breakage result in different degrees of germination; the highest degree of germination is generated by the mechanical
treatment, followed by the acid and the heat treatments, in that order. The depth of the seeds in the soil determines the
temperature thresholds and the residence times of these temperatures and whether they stimulate a massive germination at the
−1cm soil profile or only a slight germination at the −5cm depth. Seeds recently produced by the plant show higher dormancy
levels than seeds extracted from soil seed banks. Dormancy levels also depend on the shrubland age used for extracting the
soil samples (3>9years old). In effect, from the point of view of dormancy, the germination behaviour of U. parviflorus seeds seems to follow a multiresponse strategy based on different seed populations and involving both biological and abiotic
processes to break dormancy.
Dynamics of the coexisting Mediterranean species Pinus halepensis, Quercus coccifera, Erica multiflora, Rosmarinus officinalis, Cistus albidus, C. salviifolius and Ampelodesmos mauritanica, with contrasted life history traits have been studied under different fire scenarios, following two approaches: a) field survey in areas with three different fire histories (unburned for the last 31 years, once burned in 1982, and twice burned in 1982 and 1994), and b) simulations with different fire recurrence using the FATE vegetation model. We compared observed abundance in the field survey to simulation outputs obtained from fire scenarios that mimicked field fire histories. Substantial mismatching did not occur between field survey and simulations. Higher fire recurrences were associated with an increase in the resprouting Ampelodesmos grass, together with a decrease in Pinus abundance. Resprouting shrubs did not show contrasting changes, but trends of increase in Quercus and decrease in Erica were observed. The seeders Rosmarinus and Cistus achieved maximum abundance at intermediate fire recurrence. We also performed ten 200 year simulations of increasing fire recurrence with average times between fires of 100, 40, 20, 10, and 5 years. A scenario without fire was also simulated. High fire recurrence produces an increase in Ampelodesmos, a grass which is becoming dominant in the area, and a small increase in Erica, but Quercus abundance decreases and Pinus disappears. Rosmarinus and Cistus abundance peaks at intermediate fire frequencies. When comparing these simulations to those in which Ampelodesmos was excluded, we found that the absence of the grass only increased Cistus occurrence in the community, this effect being more important at frequent fire recurrence. The study suggests that simple models based on life history traits may be useful in interpreting plant community dynamics in Mediterranean ecosystems that are greatly influenced by differences in the fire regime.
Though observations on re-colonisation of post-fire sites in the Mediterranean Basin are plentiful, there still is an ongoing debate on the interrelation of fire regimes and species traits related to fire adaptation. Most of the studies found are restricted to particular species or claim to present community attributes. Therefore they often lack information for the evaluation of evolutionary evidence and historical contingency of the local fire regime and other abiotic conditions, which may act as selective pressure for plant regeneration strategies. Indeed, knowledge about the success of regeneration mechanisms and their interrelation with ecological factors is essential for the interpretation of the high spatio-temporal variability found in post-fire species performance. Such knowledge would be necessary to assess the potential of different regeneration mechanisms to cope with ongoing land-use and climate change—a crucial scientific challenge.
A summary is given of the knowledge about the limits and potential of plant regeneration mechanisms after fire in the Mediterranean Basin, along with corresponding studies conducted in other parts of the world with similar climatic conditions in order to present the fullest possible picture. Moreover, the positive or negative impacts of particular parameters of a fire regime on different regeneration strategies (post-fire seeders, resprouters, and facultative resprouters) are explained and discussed in the light of published literature. To conclude, reference is made to scientific gaps that need to be filled in order to analyse species resistance and community resilience absorbing possible climate or land use changes.
Soil samples from three microhabitats (gaps, beneath shrubs and beneath trees) in five stands of various post-fire ages (6–55years) were collected in an east Mediterranean Aleppo pine Pinus halepensis forest. Total germinable seed bank densities varied between 300 and 1300 seeds per m2. Herbaceous taxa were the major constituents of the germinable seed bank in gaps, regardless of stand age. Perennials were the major components beneath shrubs in all stands except the youngest stand where herbaceous species were the major components in all microhabitats. Important tree and shrub species (e.g., Pinus halepensis, Quercus calliprinos, Pistacia lentiscus, Phillyrea latifolia) of the mature pine forest were not an important component of the soil seed bank and therefore, little resemblance was observed between the above-ground plant species composition and soil seed bank composition. This is consistent with the fact that these species regenerate by resprouting rather than by germination from the seed bank. Both microhabitats and forest-stands, which were of different ages, contributed to the variation in taxa richness, germinable seed density and diversity among samples. The effect of small-scale spatial heterogeneity (among microhabitats) was much more pronounced. In contrast to other studies, species richness, species diversity, and density of seed banks did not decrease with post-fire age. Moreover, stand age was a poor predictor for these attributes of the soil seed bank in an Aleppo pine forest. The heterogeneity plays an important role in conservation and management of this ecosystem.
The use of regression techniques for estimating the direction and magnitude of selection from measurements on phenotypes has become widespread in field studies. A potential problem with these techniques is that environmental correlations between fitness and the traits examined may produce biased estimates of selection gradients. This report demonstrates that the phenotypic covariance between fitness and a trait, used as an estimate of the selection differential in estimating selection gradients, has two components: a component induced by selection itself and a component due to the effect of environmental factors on fitness. The second component is shown to be responsible for biases in estimates of selection gradients. The use of regressions involving genotypic and breeding values instead of phenotypic values can yield estimates of selection gradients that are not biased by environmental covariances. Statistical methods for estimating the coefficients of such regressions, and for testing for biases in regressions involving phenotypic values, are described.
Understanding the mechanics of adaptive evolution requires not only knowing the quantitative genetic bases of the traits of interest but also obtaining accurate measures of the strengths and modes of selection acting on these traits. Most recent empirical studies of multivariate selection have employed multiple linear regression to obtain estimates of the strength of selection. We reconsider the motivation for this approach, paying special attention to the effects of nonnormal traits and fitness measures. We apply an alternative statistical method, logistic regression, to estimate the strength of selection on multiple phenotypic traits. First, we argue that the logistic regression model is more suitable than linear regression for analyzing data from selection studies with dichotomous fitness outcomes. Subsequently, we show that estimates of selection obtained from the logistic regression analyses can be transformed easily to values that directly plug into equations describing adaptive microevolutionary change. Finally, we apply this methodology to two published datasets to demonstrate its utility. Because most statistical packages now provide options to conduct logistic regression analyses, we suggest that this approach should be widely adopted as an analytical tool for empirical studies of multivariate selection.
Since the early 1990s, Mediterranean gorse shrublands have expanded significantly in the Mediterranean regions of Spain mainly as a result of the increase in the frequency and extension of forest fires. Mediterranean gorse (Ulex parviflorus), which has been described as a degradation stage of forest communities after fire, has also been described as a fire-prone community. Thus, its presence increases the risk that new fires might occur. In spite of this evidence, there is little information on both the composition and structural characteristics of these communities or the relationship that might exist between these vegetation characteristics and fire behaviour. In this paper we present the results of a characterization of the vegetative structure (plant density, specific composition , biomass fractions, and horizontal and vertical fuel distribution) in Mediterranean gorse. We also analyse fire behaviour using indicators obtained at different scales. Our results show mature Mediterranean gorse shrublands to be communities with high biomass values (3000–4000 g m −2) and high horizontal and vertical vegetation continuity , in which the proportion of fine dead fuel fractions with low moisture content is around 50% of the total phytomass present. Ulex parviflorus is the dominant species and its degree of dominance is a key element in the behaviour of fire. Both the fire-line intensity values and the fire severity values observed can be considered high with respect to those observed in other Mediterranean communities, thus confirming Mediterranean gorse as a high-risk community.
Lactuca serriola L. seedlings emerge throughout the year with germination peaks in early winter and late spring. These peaks are followed closely by high levels of mortality which together produce an almost constant plant density. Plants from seeds which germinate in the winter months produce more seeds than those which germinate in spring and summer and this is considered to be associated with the duration of the rosette stage. However, the increased fecundity of the former is partially annulled by their higher mortality. It is concluded that the winter-germinated plants are the main seed producers while those which germinate in spring and summer may act as insurance against complete loss of the more fecund individuals. /// Всходы Lactuca serriola L. появляются в течение всего года с максимумом в начале зимы и в конце весны. Эти пики сопроваждаются высокой степенью отпада, что обеспечивает почти постоянный уровень плотности растений. Растения из семян, прорастающих в зимние месяцы, дают больше семян, чем растения, прорастающие весной и летом, и это рассматривается как следствие продолжительности стадии розетки. Однако, повышенная плодовитость частично аннулируется высокой степенью отпада растений. Сделано заключение, что растения, прорастающие зимой - основные продуценты семян, а те, которые прорастают весной и осенью, могут страховать возможность полного выпадения более плодовитых особей.
1. The shrubs Cistus monspeliensis and C. albidus are obligate seeders which are often dominant in Mediterranean habitats degraded by recurrent fires. 2. To determine the role of fire in the regulation of the population dynamics of these species, the germination requirements and population age-structure have been examined for populations in the South of France. 3. Germination of both species was enhanced by a change in light quality (red/farred ratio) similar to that which occurs when fire removes the light-filtering green leaves, but to a lesser extent than by a heat pretreatment designed to simulate fire temperatures. 4. In two mixed stands, one (12 years old) composed of the two Cistus species and a second (9 years old) composed of C. monspeliensis and Quercus coccifera, Cistus recruitment occurred steadily during the 5 post-fire years and then stopped. 5. For both Cistus species in the study area, age at first reproduction was 2 years, with seed production levelling off at 5 years; maximum plant longevity was around 14 years. 6. Pronounced stand decline was observed in 15-year-old stands. This was the result of a short individual plant life duration combined with restriction on new plant recruitment caused by unfavourable germination conditions. 7. The time for a stand to decline is correlated with the frequency of fire events which affect Cistus habitats. We therefore suggest that the demographic characteristics of C. monspeliensis and C. albidus stands favour their `autosuccession' through periods of increased fire hazard.
Bromus tectorum is a winter annual grass that has become extensively naturalized in western North America. Its seeds are usually at least conditionally dormant at dispersal and lose dormancy through dry afterripening. Germination response to temperature for recently harvested seeds and rate of change in germination response during afterripening were examined for collections from 21 western North American populations representing a wide array of habitats. Analysis of variance showed highly significant among-population differences in germination response variables. Principal components analysis of 20 germination variables revealed groups of populations that could be characterized by distinct response syndromes. Degree of dormancy at summer temperatures in recently harvested seeds as well as rate of dormancy loss during dry storage could be related to the risk of premature summer germination in different habitats. Mojave Desert populations showed the most clearly differentiated response. Populations from Intermountain desert and foothill habitats showed intermediate responses and did not form distinct groups. Montane populations showed the widest variation. Fully afterripened seeds from all populations were nondormant and could germinate quickly across a wide temperature range. These results demonstrate the existence of adaptively significant variation in germination response. Such variation probably represents the beginning of genetic differentiation as a result of selection among and within founder populations. Lack of a consistent relationship with habitat reflects the stochastic nature of colonization and the fact that diverse germination strategies may permit persistence, especially in less extreme habitats.
Disturbance is a dominant factor in many ecosystems, and the disturbance regime is likely to change over the next decades in response to land-use changes and global warming. We assume that predictions of vegetation dynamics can be made on the basis of a set of life-history traits that characterize the response of a species to disturbance. For crown-fire ecosystems, the main plant traits related to postfire persistence are the ability to resprout (persistence of individuals) and the ability to retain a persistent seed bank (persistence of populations). In this context, we asked (1) to what extent do different life- history traits co-occur with the ability to resprout and/or the ability to retain a persistent seed bank among differing ecosystems and (2) to what extent do combinations of fire- related traits (fire syndromes) change in a fire regime gradient? We explored these questions by reviewing the literature and analyzing databases compiled from different crown-fire ecosystems (mainly eastern Australia, California, and the Mediterranean basin). The review suggests that the pattern of correlation between the two basic postfire persistent traits and other plant traits varies between continents and ecosystems. From these results we predict, for instance, that not all resprouters respond in a similar way everywhere because the associated plant traits of resprouter species vary in different places. Thus, attempts to generalize predictions on the basis of the resprouting capacity may have limited power at a global scale. An example is presented for Australian heathlands. Considering the com- bination of persistence at individual (resprouting) and at population (seed bank) level, the predictive power at local scale was significantly increased.
The two main fire response traits found in the Mediterranean basin are the resprouting capacity (R) and the propagule-persistence capacity (P). Previous studies suggested that these two traits might be correlated. In this paper we first test whether R and P have evolved independently. Then, we ask if the correlation occurs because (a) one trait is not the target of selection but it is genetically linked to the other trait which is the one under selection pressure (indirect selection), or (b) because different evolutionary responses to the same selective pressure are acting in parallel on populations at different genetic starting points (parallel selection). Finally, we test to what extent resprouting is associated with some vegetative and reproductive traits.
To answer these questions we used a traits database for the eastern Iberian Peninsula and we assembled the phylogenetic tree on the basis of published information. The results indicate that the two traits are negatively associated and support the parallel selection scenario in which changes in R precedes changes in P. The phylogenetic–informed associations of resprouting with other traits (plant height, age at maturity) support the existence of allocation tradeoffs.
The results are consistent with the biogeographical history of the Mediterranean basin flora where most of lineages already resprouted to persist after a disturbance during the Tertiary, thus making it improbable that an additional costly persistence strategy would evolve under the Quaternary climatic conditions.
Differences in allocation patterns between seeders and resprouters in several Mediterranean plant communities (Australia, California and South Africa) have led to the prediction that seedlings of seeders grow faster than those of resprouters. In the Mediterranean Basin, it has also been hypothesized that regeneration strategy of plants after fire is associated with several other life history traits. This paper tests both hypotheses for the dominant plants in the Mediterranean Basin from literature data. Results show that seeders from the Mediterranean Basin grow significantly faster and allocate more biomass to leaf plus paracotyledons than resprouters. Seeders are mainly non‐sclerophyllous, anemochorous, dry‐fruited, small‐seeded species that evolved in the Quaternary (post‐Pliocene) and are associated with earlier successional stages. Resprouters are mainly sclero‐phyllous, vertebrate‐dispersed, fleshy‐fruited, large‐seeded species that evolved in the Tertiary (pre‐Pliocene) and are associated with late successional stages.
Field observations and models have shown: (1) differences in dispersal and dormancy strategies could account for species coexistence in disturbed environments, (2) small scale disturbances contribute to species coexistence in plant communities, and (3) recolonization success may depend on the spatial pattern of suitable sites for establishment. A spatially explicit, two-species, simulation model was developed to examine the interaction between dispersal strategies, dormancy strategies and small-scale disturbances on the pattern of coexistence of two annual plant species in patchy landscapes. Patchy landscapes with three hierarchical levers of structure were randomly generated and the dynamics for species differing in mean dispersal distance and dormancy strategy was simulated. The results showed that when species differed only in mean dispersal distance, the species with the shorter range dispersal would always displace the other. When disturbances prevented reproduction and activated dormant seeds, then differences in dormancy strategy could result in coexistence of species with different dispersal capabilities. When species differed only in their dormancy fate (i.e., the proportion of dormant seeds produced per year), the range of disturbance intensities allowing coexistence was rather narrow: but differences in the response of species to disturbance (i.e., disturbance-broken seed dormancy versus gradual germination of dormant seeds) allowed coexistence under a wider range of disturbance intensities. These results suggest that differences in the ways species exploit the resources in space and time can mediate coexistence through storage effects. The patterns of coexistence obtained in the simulations were consistent with conclusions of a field study, in species-rich Mediterranean old-fields, about the role for coexistence of the interactions among dispersal and dormancy strategies, spatial heterogeneity, and small-scale disturbances. Coexistence patterns depended on the degree of suitability and the patchiness of the landscapes, mostly in relation to the interactions between landscape structure and mean dispersal distance, but also through complex interactions with dormancy characteristics. Therefore, disturbance regimes are not sufficient for predicting patterns of coexistence, and the unique spatial features of the landscapes need to be taken into account.
Soil degradation and desertification are key problems,facing Mediterranean ecosystems,and these have worsened recently with the increasing frequency of fires. Moreover, rainfall in western Mediterranean areas is characterized by high intensity, and extreme rainfall events after fire strongly affect the equilibrium between soil erosion and vegetation recovery. These facts led us to carry out experimental fires in a fire-prone vegetation community (dominated by Mediterranean gorse, Ulex parviflorus Pourr.) to study the effect of a torrential rainfall event (through rainfall simulation) on the short-term vegetation regeneration process (seedling emergence,and survival). The results indicate that, in Mediterranean gorse shrublands after fire, an extreme precipitation event does not affect seedling emergence (either through seed loss or from seed germination). In contrast, it has a significant effect on the reduction of seedling survival both from direct impact (seedlings buried by sediment or seedlings totally or partially unearthed) and indirectly as a result of soil and litter losses. As a consequence, the combination of fire and torrential rainfall has an important and persistent effect on vegetation recovery, and may cause further degradation, which eventually becomes irreversible. Additional keywords: erosion; experimental fire; rainfall simulation; Ulex parviflorus.
Aim Determining how differences in time of germination can affect plant establishment in plant communities that, after a disturbance, must reestablish from seeds under climatic conditions subject to extremes, such as the Mediterranean. Although early germination may be beneficial for survival in summer, when drought is severe, this may expose the seedlings to winter extremes, thus to higher mortality. Understanding how sensitive is the establishment of different species to temporal patterns of germination will help to understand the factors that control species distribution and community stability in disturbance‐prone environments, as well as its sensitivity to changes in weather patterns as climate changes.
Methods An experimental fire was made in early fall in an old Cistus–Erica shrubland in Toledo (central Spain). After fire, germination, survival and growth of the three dominant seeder species ( Cistus ladanifer , Erica umbellata and Rosmarinus officinalis ) were monitored during the first 3 years after fire. Seedlings were tagged to identify their time of emergence, and divided into cohorts according to their month of germination. Differences in survival of the various cohorts were evaluated by means of a Wilcoxon (Gehan) statistic. Height of surviving, tagged plants was compared among cohorts by means of a Kolmogorov–Smirnov test.
Results The year following fire was one of the driest on record, while the next one was one of the wettest. Germination was more abundant during the first than during the second year. Establishment was mainly from first‐year germination, as the majority of second‐year germinated seedlings died. Temporal patterns of germination within a year and between years varied between species. Seedling mortality was highest immediately following germination, not in summer. Mortality was related to time of germination: during a given period of time, the mortality of younger seedlings was higher than that of older ones. However, survival was not highest for the first cohorts. In general, the earlier the seedlings germinated the more vigourous they became, more clearly so for Cistus than for Rosmarinus , but differences tended to disappear with time. Overall, time of germination varied between species and affected differently seedling survival and vigour of the various species. Rosmarinus and Cistus had sufficient survivors to reestablish the initial population. Erica , despite abundant germination, suffered a strong population reduction.
Main conclusions Mediterranean shrub species differ in their temporal patterns of germination and survival after fire. The effect of time of germination is complex: germinating early is advantageous since old seedlings fared better than younger ones when confronted with the same rigours. However, germinating early might expose the seedlings to greater hazards and the first cohort might not survive best. The temporal window for establishment is narrow and mainly restricted to the first year after fire. Second year seedlings, irrespective of most favourable conditions, survived very little. Missing the window of establishment might virtually lead to a population collapse, despite having very high germination, as found for Erica .
In Western Mediterranean areas, forest fires are frequent in forests established on old croplands where post-fire regeneration is limited to obligate-seeder species. This has re-sulted in the spread of Mediterranean gorse (Ulex parviflorus) increasing the risk and sever-ity of fires. The aim of this paper is to test the autosuccessional hypothesis on a Mediter-ranean gorse shrubland dominated by seeders species. Particular objectives are: a) to analyze the effect of fire on seedling emergence, survival and growth on the main species involved on plant regeneration process. b) to identify changes in the relative abundance of species as consequence of fire by using a before–after experiment. Then, after experimen-tal fires, seedling emergence, survival and growth rates were analyzed for the main spe-cies present in the vegetation regeneration process. Our results show that Mediterranean gorse communities are dominated by Fabaceae species (64% of individuals, mainly of Ulex parviflorus). However, our study demonstrates that vegetation regeneration after fire does not display an autosuccessional pattern and is produced a change on dominance from Fa-baceae (mainly U. parviflorus) to Cistaceae (mainly C. albidus) species. Cistaceae seedlings (mainly Cistus albidus and Helianthemum marifolium) were the most abundant post-fire (63% of total germination) while species of Fabaceae (including U. parviflorus and Ononis fruticosa) represented 25%, and Lamiaceae (restricted to Rosmarinus officinalis) comprised only 3% of total emergences. Seedling survival did not differ significantly from one spe-cies to another (25–30% of initial individuals over 3 years) but seedling growth rates were also higher for Cistaceae than for Fabaceae individuals. Then, after fire, in terms of bio-mass, Fabaceae presence decreased from 78.7% to 13.1% while Cistaceae increase from 8% to 83.4%. Given that fire frequency, intensity or severity is partially controlled by the composition and structure of the plant community population changes in the main spe-cies, could affect the future fire regime and in turn, affect the hydrological, ecological and economic role of a large stretch of forest and woodland areas in western Mediterra-nean ecosystems.
Species‐specific responses to the range of microsites resulting from canopy gap formation may contribute to coexistence in tropical forests. We investigated the effects of four factors affected by canopy gap formation (red : far‐red light, soil nitrate concentrations, soil temperature fluctuations and soil water potential) on the germination response of four pioneer Piper species ( P. dilatatum , P. hispidum , P. marginatum and P. peltatum ) that are typically found in canopy gaps and clearings.
All four Piper species required light for maximum germination. However, the ratio of red : far‐red light (R : FR) resulting in maximum germination varied between species. Piper peltatum will germinate in simulated understorey light conditions; P. dilatatum and P. hispidum require conditions typically found in small to medium gaps; while P. marginatum requires the conditions appropriate to large gaps.
Only P. marginatum was affected by nitrate concentration: elevated concentrations increased the germination rate. This suggests that this species could detect canopy gaps using a combination of high R : FR and elevated soil nitrate concentrations.
The germination rate of P. marginatum was least sensitive to low water potentials and high daytime temperatures characteristic of large gaps. Piper peltatum was most sensitive to these treatments, while P. dilatatum and P. hispidum were intermediate in response.
A principal components analysis of the ratios of germination in understorey to large gap conditions, for four variables, generated a significant axis that explained 88·5% of the variance in germination response between species. Differential species distribution along this axis, based on species‐specific responses, may allow germination to occur in the most suitable microsite for onward growth of the seedling and contribute to species coexistence by reducing interspecific competition.
Summary 1. Many Mediterranean plant species persist after fire because their seeds are protected from the heat of the fire (e.g. hard-coated seeds, serotinous cones), thus permitting rapid post-fire recruitment. For simplicity, this trait will hereafter be called P and its two possible phenotypes P+ (seeder) and P- (non-seeder). 2. Because P+ appears in a narrow taxonomic spectrum and confers persistence under high fire frequencies, we test the extent to which communities with different fire histories have different phenotypic and phylogenetic structures. Specifically, we compare coastal vegetation growing in a warm and dry Mediterranean climate subject to high fire frequency (HiFi vegetation) with montane vegetation subject to a subhumid climate where fires are rare (LowFi) under the hypothesis that P+ species will be over-represented in HiFi communities, thus producing phenotypic and phylogenetic clustering. 3. Trait conservatism on P is evaluated by testing the presence of a phylogenetic signal, phenotypic clustering is tested by correlating co-occurrence and phenotypic distance matrices, and the phylogenetic structure is evaluated by testing whether the phyloge- netic distances between species in each community are different from those expected by chance. 4. The results suggest that: (a) P is a strongly conserved trait; (b) co-occurring species have similar P phenotypes (phenotypic clustering); and (c) the phylogenetic structure in HiFi vegetation is significantly clustered while LowFi vegetation tends to be overdispersed. 5. Synthesis : Fire is a strong driving force in assembling HiFi communities while other forces, such as competitive interactions, are the main assembly mechanisms in LowFi communities. This result supports the role of recurrent disturbances as filters driving phylogenetic community structure.
Wildland fires and torrential rainfall are important factors affecting Mediterranean nature and human society. In this paper, we investigate their combined impact on a fire-prone vegetation community at the east coast of Spain. Our results show that shrub cover provides an effective control of erosion even under simulated extreme rainfall events. After fire, soil erosion increased noticeably; however, the amount of sediment produced varied greatly, which can be explained by variations in fire severity. The quantity of litter debris after the fire plays a decisive role in controlling the erosion that follows. Copyright © 2003 John Wiley & Sons, Ltd.
Comparative studies of the genetic architecture of different types of traits were initially prompted by the expectation that traits under strong directional selection (fitness traits) should have lower levels of genetic variability than those mainly under weak stabilizing selection (nonfitness traits). Hence, early comparative studies revealing lower heritabilities of fitness than nonfitness traits were first framed in terms of giving empirical support for this prediction, but subsequent treatments have effectively reversed this view. Fitness traits seem to have higher levels of additive genetic variance than nonfitness traits — an observation that has been explained in terms of the larger number loci influencing fitness as compared to nonfitness traits. This hypothesis about the larger functional architecture of fitness than nonfitness traits is supported by their higher mutational variability, which is hard to reconcile without evoking capture of mutational variability over many loci. The lower heritabilities of fitness than nonfitness traits, despite the higher additive genetic variance of the former, occur because of their higher residual variances. Recent comparative studies of dominance contributions for different types of traits, together with theoretical predictions and a large body of indirect evidence, suggest an important role of dominance variance in determining levels of residual variance for fitness-traits. The role of epistasis should not be discounted either, since a large number of loci increases the potential for epistatic interactions, and epistasis is strongly implicated in hybrid breakdown.
Abstract Seasonal germination timing strongly influences lifetime fitness and can affect the ability of plant populations to colonize and persist in new environments. To quantify the influence of seasonal environmental factors on germination and to test whether pleiotropy or close linkage are significant constraints on the evolution of germination in different seasonal conditions, we dispersed novel recombinant genotypes of Arabidopsis thaliana into two geographic locations. To decouple the photoperiod during seed maturation from the postdispersal season that maternal photoperiod predicts, replicates of recombinant inbred lines were grown under short days and long days under controlled conditions, and their seeds were dispersed during June in Kentucky (KY) and during June and November in Rhode Island (RI). We found that postdispersal seasonal conditions influenced germination more strongly than did the photoperiod during seed maturation. Genetic variation was detected for germination responses to all environmental factors. Transgressive segregation created novel germination phenotypes, revealing a potential contribution of hybridization of ecotypes to the evolution of germination. A genetic trade-off in germination percentage across sites indicated that determinants of fitness at or before the germination stage may constrain the geographic range that a given genotype can inhabit. However, germination timing exhibited only weak pleiotropy across treatments, suggesting that different sets of genes contribute to variation in germination behavior in different seasonal conditions and geographic locations. Thus, the genetic potential exists for rapid evolution of appropriate germination responses in novel environments, facilitating colonization across a broad geographic range.
Mediterranean ecosystems are hotspots of species richness where fire is one of the key processes influencing their structure, composition and function. Post-fire seedling emergence constitutes a crucial event in the life cycle of plants and species-specific temporal and spatial patterns of seedling emergence have been hypothesized to contribute to the high diversity in these ecosystems. Here we study the temporal and spatial patterns of seedling emergence observed for the four dominant species (Cistus albidus, Ulex parviflorus, Helianthemum marifolium, Ononis fruticosa) after an experimental fire in a Mediterranean gorse shrubland. In a first analysis we compared the timing of emergence of each species using the Kaplan-Meier method. The spatial component of seedling emergence and the spatiotemporal relationship between different cohorts of the same species were analyzed using recent techniques of spatial point pattern analyses. We found a bimodal temporal pattern of emergence. Emergence of Cistaceae species (H. marifolium and C. albidus) occurred predominantly early after the fire while Fabaceae (O. fruticosa and U. parviflorus) emerged mainly during the following autumn. Individually, all species showed an aggregated spatial pattern and, when testing for pair interactions, we found that the clusters of individual species were spatially segregated. Additionally, the clusters of individual species showed an internal spatial structure where seedlings of different cohorts were spatially segregated. Theoretical models predict that these patterns will promote species coexistence. We identified a number of mechanisms that all have the potential to contribute to the observed pattern formation. However, the potential interaction among these mechanisms are complex and not easy to predict. Our analyses take a significant step forward in studying seedling emergence in fire prone ecosystems since, to our knowledge, this is the first time that both spatial and temporal patterns of all dominant species have been studied together.
The comparison of the degree of differentiation in neutral marker loci and genes coding quantitative traits with standardized and equivalent measures of genetic differentiation (FST and QST, respectively) can provide insights into two important but seldom explored questions in evolutionary genetics: (i) what is the relative importance of random genetic drift and directional natural selection as causes of population differentiation in quantitative traits, and (ii) does the degree of divergence in neutral marker loci predict the degree of divergence in genes coding quantitative traits? Examination of data from 18 independent studies of plants and animals using both standard statistical and meta-analytical methods revealed a number of interesting points. First, the degree of differentiation in quantitative traits (QST) typically exceeds that observed in neutral marker genes (FST), suggesting a prominent role for natural selection in accounting for patterns of quantitative trait differentiation among contemporary populations. Second, the FST – QST difference is more pronounced for allozyme markers and morphological traits, than for other kinds of molecular markers and life-history traits. Third, very few studies reveal situations were QST < FST, suggesting that selection pressures, and hence optimal phenotypes, in different populations of the same species are unlikely to be often similar. Fourth, there is a strong correlation between QST and FST indices across the different studies for allozyme (r=0.81), microsatellite (r=0.87) and combined (r=0.75) marker data, suggesting that the degree of genetic differentiation in neutral marker loci is closely predictive of the degree of differentiation in loci coding quantitative traits. However, these interpretations are subject to a number of assumptions about the data and methods used to derive the estimates of population differentiation in the two sets of traits.
This paper discusses the interactions among prefire shrub abundance, soil moisture, and plant and animal species on postfire seedling establishment in mixed chparral in southern California. Postfire germination and survival of seedlings in a stand dominated by a facultative seeder (Adenostoma fasciculatum) and by an obligate seeder (Ceanothus greggii) were monitored for 2 years. Relative to prefire abundance, germination of C. greggii was higher than that of A. fasciculatum. Survival during the first year was also higher in C. greggii than in A. fasciculatum. During the second year, however, mortality of C. greggii was greater than that of A. fasciculatum, mostly due to a psyllid infection. Germination of A. fasciculatum was negatively related to prefire shrub abundance. C. greggii germination was not associated with prefire shrub abundance. Seedling mortality of both species was very strongly related to the depletion of soil moisture the first few months after germination. A. fasciculatum was more sensitive than C. greggii to the drying of the soil, especially in the upper levels. C. greggii seedlings had longer roots, greater root/shoot biomass ratios, higher water potentials, and a later peak in seasonal growth activity compared to A. fasciculatum. Herbs promoted greater survival of A. fasciculatum. Our results indicate that the obligate seeder species, C. greggii, is better adapted to establish seedling in chaparral by producing greater relative germination and greater seedling survival than the facultative seeder species A. fasciculatum. The greater adaptability of C. greggii to the physical environment is counteracted by interspecific interference by plant and animal interactions which tend to favor A. fasciculatum over C. greggii.
Summer wildfires and autumn torrential rainfall are the background to the development of one of the most important environmental problems in the western Mediterranean area: erosion, degradation of soil structure and desertification. These processes especially affect plant communities located in old abandoned fields where woody sprouters are practically absent. Under these conditions, post-fire vegetation cover is dependent on obligate seeders and, in the short term, especially on resprouting perennial grasses. Brachypodium retusum is a rhizomatous perennial grass that plays a particularly important role in the resilience of these fire-prone Mediterranean ecosystems. In Mediterranean gorse shrublands, during the first few years after a fire, this species represents 90% of plant cover and biomass. The recurrence or severity of fire does not seem to affect the regeneration capacity of this species. After two years, even under high fire frequency (12 years) and high fire severity (> 400C), it recovers both cover and biomass. Nevertheless, this species, a key factor in the control of soil erosion, is extremely affected by erosion processes. A single extreme rainfall event reduces the rate of regeneration of B. retusum by about 50%. The reduction in the protective cover of this species may result in degradation and eventual self-induced degrading process in the ecosystem.
Seedlings of Acer rubrum, Carpinus caroliniana, and Platanus occidentalis were germinated and grown under contrasting light regimes: varied light (59% of the abovecanopy photon flux incrementally decreased to 9%, simulating a forest understory during canopy leaf-out) and low light (constantly less than 10%, simulating an understory after leaf-out). By the time that light in both treatments was equilibrated at 9%, 44 days after the first germination, varied light plants were an order of magnitude larger than low light plants. However, in the remainder of the experiment, during which all plants were kept at 9% light, varied light plants had lower relative growth due to: 1) lower leaf area per unit of plant mass; and 2) lower net productivity per unit of leaf area. A subset of plants were flooded after light equilibration, resulting in reduced growth. Varied and low light plants were equally affected by flooding. Reported differences among species in shade tolerance were poorly correlated with differences in response to light treatment.