No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Species-specific facilitation, ontogenetic shifts and consequences for plant community succession
Abstract and Figures
Abstract
Aims
Our main aims are to test how: (1) different nurse species modulate the early establishment of multiple beneficiary species in a degraded area; (2) the intensity and direction of species-specific interactions between nurse and beneficiary species change during beneficiary ontogeny.
Location
A shrubby Caatinga forest at Petrolina, northeast Brazil, degraded by grazing and logging activities in recent decades.
Methods
We conducted a factorial multi-species experiment in which seeds and seedlings of five beneficiary species were sown in the presence and absence of three pioneer tree species. Beneficiary species performance was monitored for different ontogenetic stages.
Results
We found evidence of species-specific facilitation in which the intensity and outcome of the interactions between nurse and beneficiary species varied depending on species identity. Additionally, for most combinations of nurse and beneficiary species, ontogenetic shifts from positive to neutral or negative interactions were observed with increasing beneficiary age.
Conclusions
We provide experimental evidence that nurse and beneficiary species identity simultaneously influence the balance between facilitation and competition. Our results suggest that ontogenetic shifts may be a widespread phenomenon in semi-arid ecosystems. We discuss that a key mechanism explaining these findings is the match between what nurse species offer and what beneficiary species require in terms of resources and conditions. As a consequence, different nurse species tend to favour or inhibit unique sets of beneficiary species beneath their canopies. We argue that species-specific facilitation is an overlooked mechanism promoting β-diversity during community succession.
Figures - uploaded by Gustavo Brant Paterno
Author content
All figure content in this area was uploaded by Gustavo Brant Paterno
Content may be subject to copyright.
Supplementary resources (5)
... Such process is commonly reported for stressful environments such as arid, semiarid and alpine ecosystems (Valiente-Banuet and Verdu, 2007;Gómez-Aparicio, 2009;Cavieres et al., 2016). Facilitation strength is frequently described as being species-specific or to depend on the identity of the nurse-target species combination (Landero and Valiente, 2010;Michalet et al., 2015;Paterno et al., 2016;Fagundes et al., 2018). However, in order to advance our understanding of such positive interactions, and gain theoretical generality, one needs to abandon the taxonomic perspective to adopt a functional approach (Soliveres et al., 2015;Paterno et al., 2016). ...
... Facilitation strength is frequently described as being species-specific or to depend on the identity of the nurse-target species combination (Landero and Valiente, 2010;Michalet et al., 2015;Paterno et al., 2016;Fagundes et al., 2018). However, in order to advance our understanding of such positive interactions, and gain theoretical generality, one needs to abandon the taxonomic perspective to adopt a functional approach (Soliveres et al., 2015;Paterno et al., 2016). Behind the apparent idiosyncrasy of the facilitation strength exhibited by species-pairs, we expect to find general rules associated to nurse-target functional trait matches. ...
... In drylands, most studies on the effects of nurse plants typically focus on shrubs or short cushions (Landero and Valiente-Banuet, 2010;Soliveres and Maestre 2010;Schöb et al., 2017), but trees can also act as nurses (Paterno et al., 2016;Fagundes et al., 2018). However, we have a limited understanding of how facilitation acts in the dry ecosystems of South America, as most studies are conducted in Andean regions (Cavieres and Badano, 2009;Catorci et al., 2016;Danet et al., 2017;Gavini et al., 2020). ...
Functional trait combinations underlie assembly rules of plant communities. In harsh environments, facilitation is widespread but its strength varies greatly between pairs of interacting nurse-target plants. Here, we investigated whether functional traits of potential nurse and target species can jointly predict the sign and strength of their interactions. In order to estimate the facilitation strength for 60 nurse-target species combinations, we conducted field experiments in a seasonally dry tropical forest. We estimated eight key functional traits (canopy diameter, leaf C:N, leaf ∂C13, specific leaf area, number of months without leaves, wood density, hydraulic diameter and root volume) for 20 potential mature nurse species established under field conditions. For three target species, four key functional traits were estimated for seedlings grown in greenhouse conditions (total dry biomass, plant water content, root:shoot ratio, and apical growth rate). Our results showed that facilitation strength can be explained by the interaction between nurse and target traits. Facilitation increased when low SLA nurses interacted with targets investing in apical growth, thus acquisitive targets are benefited by the greater availability of resources left by conservative nurses. Facilitation also increased when nurses with lower values of leaf ∂C13 interacted with high root:shoot ratio targets, so early release of light and soil resources due to nurse earlier leaf loss benefits drought resistant targets. Besides, root volume of the nurse promoted facilitation, probably due to improvements on soil conditions. Functional trait match can shed light on plant community assembly rules and help promote ecosystem restoration and management.
... Nurse plants are usually more tolerant of thermal and/or light stress, which are common in areas undergoing the initial process of secondary succession, and modify the environmental conditions and the resource availability to the facilitated species (Kitao et al. 2000;Henríquez & Lusk 2005), promoting an increase in local diversity (Padilla & Pugnaire 2006;Vieira et al. 2013;Paterno et al. 2016;Macek et al. 2017). Although great efforts have been made to understand the mechanisms defining facilitation (Soliveres et al. 2015;Derroire et al. 2016;Kéfi et al. 2016), most studies focus only on the physical changes to the environment promoted by facilitator species (Derroire et al. 2016). ...
... Some studies use mathematical indices, such as the relative interaction index (RII) (Armas et al. 2004), which estimate the competitive skills of plants in an interaction based on species productivity values (Aakala et al. 2013;Fagundes et al. 2018). In semi-arid environments, studies showed that pioneer species enable a higher growth of the regenerating species established under their canopies by creating more favourable microenvironments and increasing water availability (Paterno et al. 2016;Macek et al. 2017). On the contrary, some studies also showed that competition for nutrients and water had a negative effect on the growth of neighbouring species (Jensen et al. 2011;Fernández & Altesor 2017). ...
... Some studies conducted in arid and semi-arid environments show the positive effect of pioneer and early-successional species on the growth of juvenile plants. Indeed, they relate higher plant growth to abiotic changes promoted by the canopy, such as increased shading (Miriti et al. 2006;Paterno et al. 2016;Fagundes et al. 2018). In contrast, other tree species can show a high competitive ability in obtaining resources, besides not improving environmental conditions. ...
Early-successional tree species may facilitate the establishment of the regenerating plant community in semi-arid environments by creating more favourable microenvironments and reducing environmental stress. However, it is not clear how these tree species can influence morphofunctional and physiological responses of the regenerating plant community. In field conditions, we used three early-successional tree species in the adult stage (Combretum leprosum, Cenostigma bracteosum and Mimosa tenuiflora) as potential facilitators, and two regenerating ones as target species (Cordia oncocalyx and Croton blanchetianus). We then evaluated the effect of the former on the leaf anatomy, physiology and growth of the latter. We found that C. leprosum and C. bracteosum acted as facilitators, resulting in a 55% and 22% reduction in solar radiation in the rainy season, and an 11% and 10% reduction in the dry season, respectively. In addition, we observed a higher soil moisture under the canopy of nurse species, especially under C. leprosum, which showed an increase of over 38% in gravimetric water content in the rainy and dry seasons. These results favoured gas exchange (CO2 uptake, stomatal conductance and transpiration) and growth in Cordia oncocalyx and C. blanchetianus. Furthermore, we did not observe any stress reduction under the canopy of M. tenuiflora and in the open area, where target species showed reduced gas exchange and growth. The positive morphological and ecophysiological responses of the target species under C. leprosum and C. bracteosum reinforce the importance of studying microenvironments created by early-successional tree species. This way, we can understand the mechanisms promoting facilitation and the influence of this positive interaction on the restructuring process of the plant community in a semi-arid environment.
... Em ambientes com condições abióticas adversas e recursos limitados e.g. regiões áridas e semiáridas, estudos apontam que as relações positivas entre plantas são predominantes, como a facilitação (Weltizin & McPherson 1999;Callaway et al. 2002;Araujo 2014;Paterno et al. 2016). Plantas facilitadoras também conhecidas como enfermeiras são pioneiras no processo de regeneração, e favorecem o estabelecimento de outras plantas mais sensíveis, utilizadas nos modelos de restauração florestal (Callaway 1995;Associação Caatinga 2011;Vieira et al. 2013). ...
... Além disso, diferentes plantas enfermeiras podem favorecer o estabelecimento de diferentes espécies beneficiárias, estabelecendo relações espécie-específicas, que afetam a composição florística e a diversidade das comunidades (Zimmer et al. 2010;Paterno et al. 2016). ...
... A relação positiva de enfermeira-beneficiária pode variar com as características das comunidades e ecossistemas, tornando-se neutra ou mesmo negativa conforme o estágio de desenvolvimento ontogenético das plantas beneficiárias; pois, plantas adultas tendem a competir com as enfermeiras (Miriti 2006;Paterno et al. 2016). Evidências demonstram que durante a sucessão ecológica ocorre a substituição de espécies, em geral, aumentando a complexidade na estrutura da comunidade e promovendo maior disponibilidade de microambientes para espécies (Peroni & Hernández 2011). ...
... The SGH in its original form predicts that positive interactions increase with increasing environmental severity (Bertness and Callaway 1994). While there is significant empirical evidence supporting this linear model (Armas et al. 2011;Kawai and Tokeshi 2007;Callaway et al. 2002; also see He et al. 2013 and references therein), other studies have found that facilitation follows a humpback (unimodal) model transitioning into competition as beneficiaries mature to reproductive age (Gasque and Garciá-Fayos 2004;Miriti 2006;Niinemets 2010;Paterno et al. 2016), conditions become too stressful (Maestre and Cortina 2004;Michalet et al. 2006Michalet et al. , 2014 or alternatively, facilitation collapses and interactions become neutral (Koyama et al. 2013;Michalet et al. 2014;Kjaer et al. 2018;Zhang et al. 2018). ...
... Ratios are given from a negative binomial generalized mixed model and back-transformed from the log scale a variable more closely linked to demography as suggested by Malkinson and Tielbörger (2010). Species specificity clearly plays an important role in determining facilitation outcomes as studies using multiple species analyses have suggested (Liancourt et al. 2005;Paterno et al. 2016;Liczner et al. 2017). Species-specific changes in performance across stress gradients, where nurse shrub amelioration is limited by a physiological threshold of the beneficiary, was conceptualized by Soliveres et al. (2015) and derived largely from an earlier study by Liancourt et al. (2005) in mesoxeric grasslands of eastern France. ...
... Daily shifts in leaf water potential can be a mechanism of facilitation (Wright et al. 2015) driving microsite amelioration around shrubs through increased humidity and cooling of air and soil (Holmgren 2000;Quero et al. 2006) further limiting transpiration. These mechanisms are a possibly why A. thurberianum is considered highly tolerant to drought, and supports the empirical studies that evidenced species-specific responses depend on the resources needed by that species being matched by the resources provided by the nurse plant (see Montgomery et al. 2010 andPaterno et al. 2016 for example). Sagebrush shrubs extract soil moisture at deeper levels than perennial bunchgrasses (Inouye 2006) and have been shown to increase surface soil moisture (Richards and Caldwell 1987) and nitrogen uptake into inflorescences through hydraulic lift (Cardon et al. 2013). ...
Plant reproduction is highly sensitive to stress from severe weather. While facilitation has been shown to buffer negative impacts along stress gradients, less is known about facilitating plant reproduction in drought periods. Because intensity and frequency of drought are predicted to increase, plant reproductive facilitation has important implications for a species ability to adapt to changes in climate. Our primary study objective is to test if nurse shrubs act as reproductive micro-refugia across soil types, by improving reproductive potential of perennial bunchgrass neighbors subjected to severe drought. To investigate this objective, we designed a fully factored study testing direct interaction between shrub and bunchgrasses in eastern Oregon sagebrush steppe, at two sites with different soil types. The study consisted of six simple effect treatments combining three moisture regimes (moist, ambient, and drought) with two shrub conditions (shrub intact or shrub removed). Our results indicate when facilitation of reproductive potential occurs, it occurs strongly and particularly in drought, consistent with the stress gradient hypothesis (SGH), where several species produced at least 54% more inflorescences in the presence of shrub neighbors. In addition, we found facilitation to be consistent with the SGH at the species level likely reflecting differences in plant strategy and perception of strain, but to follow alternative SGH models more closely at the site level where facilitation declined on the drier soil. Ultimately, our findings highlight the importance of facilitation in improving plant reproductive potential in drought, and support the role of nurse shrubs as micro-refugia in a changing climate.
... Nurse effects, however, might vary from positive to negative depending on the target species that establishes under nurse crown, and this process is referred as a species-specific interaction outcome (Callaway, 1998;Callaway & Walker, 1997). Species-specific interaction outcomes have been found to occur in a wide range of ecosystems (Landero & Valiente-Banuet, 2010;Paterno, Siqueira, & Ganade, 2016;Poulos, Rayburn, & Schupp, 2014) and have been pointed out as a strong factor modulating seedling regeneration in plant communities (Paterno et al., 2016). However, predicting the outcome of nurse-target interactions can be difficult, especially in high diversity ecosystems where multiple pairs of nurse and target species are able to interact. ...
... Nurse effects, however, might vary from positive to negative depending on the target species that establishes under nurse crown, and this process is referred as a species-specific interaction outcome (Callaway, 1998;Callaway & Walker, 1997). Species-specific interaction outcomes have been found to occur in a wide range of ecosystems (Landero & Valiente-Banuet, 2010;Paterno, Siqueira, & Ganade, 2016;Poulos, Rayburn, & Schupp, 2014) and have been pointed out as a strong factor modulating seedling regeneration in plant communities (Paterno et al., 2016). However, predicting the outcome of nurse-target interactions can be difficult, especially in high diversity ecosystems where multiple pairs of nurse and target species are able to interact. ...
... However, predicting the outcome of nurse-target interactions can be difficult, especially in high diversity ecosystems where multiple pairs of nurse and target species are able to interact. Nurse plants may also have positive effects on target survival but negative or neutral effects on growth (Gómez-Aparicio, 2009;Paterno et al., 2016), making the interaction predictions even more complex. Therefore, there is an urgent need to identify the nurse traits that influence target performance. ...
Plant establishment is a challenge in semiarid environments due to intense and frequent drought periods. The presence of neighboring trees (nurses) can increase the establishment of seedlings (targets) by improving resource availability and microclimate. The nurse effect, however, might vary depending on nurse‐target species combinations but factors that predict this specificity are poorly known. We used a multispecies experiment to investigate the facilitation potential of trees from a range of successional stages, focusing on how nurse functional traits can predict species‐specific interaction outcomes. We conducted a factorial field experiment in a Brazilian semiarid tropical forest during a severe drought period. Sixty pairs of interacting tree species, 20 potential nurses, and three targets were used. Seedlings of all targets were planted both under and far from the nurse canopy, in a randomized block design replicated five times. Target growth and survival were monitored for 275 days from the beginning of the dry season, and interaction outcomes were calculated using the Relative Interaction Intensity (RII) index. Nurse functional traits such as successional stage, height, wood density, and canopy diameter were used as explanatory variables to predict RII values. The average effect of nurse species on target plants was in general positive, that is, seedling survival and growth increased under the nurse canopy. However, for growth pairwise interactions were significantly species specific. Successional stage was the only functional trait explaining RII values, with pioneer tree species being stronger facilitators than later successional trees. However, the explanation power of this variable was low, and positive, negative, or neutral interactions were found among nurse trees of all successional stages. Because seedling mortality during drought in semiarid systems is high, future studies should investigate how nurse traits related to water use could influence nurse facilitation skills. Community level experiment on nurse tree potential shows species‐specific relations. Successional stage partially explains nurse facilitation capability. However, seedlings in this semiarid system experienced high mortality regardless of positive tree neighbor effects.
... Immediately after glacier retreat, soils are generally nutrient poor and affected by surface instability, but early colonizers do not inhibit the establishment of new colonizing taxa 1 . This may be explained either by neutral interactions (due to the predominant role of the environment 57 or of stochastic processes 9,10 ) in these species-poor early stages, or by facilitative interactions 1 where the beneficiary species are not constraining the already established ones 58 . However, the importance of taxa addition quickly decreased over time and replacement became the dominant pattern for late-successional stages, suggesting increasing competition, as expected when resources, species richness and cover increase 27 . ...
... In late-successional stages, the stabilization of nutrients and terrains can allow new and more competitive alpine taxa to establish and replace pioneer species 34 . Such substitutions may occur either because early arrivers modify the environment, making the conditions less suitable for themselves compared with other colonizers 1 , or because later successional species outcompete the already established early species 34,58 . ...
The mechanisms underlying plant succession remain highly debated. Due to the local scope of most studies, we lack a global quantification of the relative importance of species addition ‘versus’ replacement. We assessed the role of these processes in the variation (β-diversity) of plant communities colonizing the forelands of 46 retreating glaciers worldwide, using both environmental DNA and traditional surveys. Our findings indicate that addition and replacement concur in determining community changes in deglaciated sites, but their relative importance varied over time. Taxa addition dominated immediately after glacier retreat, as expected in harsh environments, while replacement became more important for late-successional communities. These changes were aligned with total β-diversity changes, which were more pronounced between early-successional communities than between late-successional communities (>50 yr since glacier retreat). Despite the complexity of community assembly during plant succession, the observed global pattern suggests a generalized shift from the dominance of facilitation and/or stochastic processes in early-successional communities to a predominance of competition later on.
... The intensity of the facilitation effect can vary between species with different functional traits in tropical drylands (Fagundes et al., 2018;Graff & Aguiar, 2017;Paterno et al., 2016). Knowledge of which plant traits would represent key drivers of facilitation could be useful in defining sets of plant species that, when together, enhance restoration performance. ...
... This early effect, however, is not commonly explored, since studies usually focus on the facilitative effects of larger/older plant species on smaller/younger ones (Fagundes et al., 2018;Fedriani et al., 2019;Gómez-Aparicio et al., 2004;Paterno et al., 2016). Studies on the influence of adult trees on seedlings are more common because older plants are expected to cause more drastic effects on the environment than younger individual plants (Navarro-Cano et al., 2015). ...
Restoration programmes that promote the functioning of restored ecosystems are in urgent demand. Although several biodiversity and ecosystem functioning (BEF) experiments have demonstrated the importance of functional complementarity in enhancing plant community performance, no biodiversity experiment has yet manipulated facilitation to test its contribution to how the complementarity effect (CE) modulates community performance.
We built a restoration experiment manipulating diversity and facilitation potential in a tropical semi‐arid forest. We planted 4704 seedlings of 16 native tree species to assemble 147 experimental communities with 45 different compositions comprising 1, 2, 4, 8 or 16 species. Facilitation potential was included in the experimental design by creating a gradient of communities from low to high facilitation potential (based on prior research). We measured functional dispersion and functional identity using species above‐ and below‐ground traits to investigate how they modulate the effects of species diversity and facilitation potential on leaf biomass production, using the additive partition biodiversity effects CE and selection effect (SE).
The joint influence of diversity and facilitation potential was tested separately for leaf biomass production and net biodiversity effect using linear mixed models (LMMs). We subsequently ran LMMs including functional dispersion and functional identity. We hypothesised that facilitation potential would increase community productivity and functioning and that functional dispersion and functional identity related to above‐ and below‐ground traits would explain facilitation performance.
Facilitation potential positively influenced leaf biomass production as predicted, but unexpectedly, neither of the functional traits were important for modulating the facilitation process. Positive values for CE showed that plants performed better in mixtures in comparison to monocultures. SE negative values, showed that species with below average performance in monocultures, performed better in mixtures. Unexpectedly, CE did not increase as species diversity or facilitation potential increased. The SE was influenced negatively by facilitation potential leading to a more equal distribution of biomass production between species in mixtures.
Synthesis. Facilitation improves biomass production in restored communities and increases biomass equitability among plant species and thus ecosystem reliability. To improve restoration success, plant communities should be built using a combination of facilitative species.
... Immediately after glacial retreat, soils are generally nutrient-poor and affected by physical disturbances but early colonizers do not inhibit the establishment of new colonizing taxa 1 . This may be explained either by neutral interactions (due to the predominant role of the environment 46 or of stochastic processes 9,10 ) in these species-poor early stages or by facilitative interactions 1 , where the bene ciary species are not constraining the already established species 47 . However, the importance of taxa addition quickly decreased over the succession sequence, suggesting an increasing competition, as expected when environmental harshness decreases and species richness and cover increases 23 . ...
... In late successional stages, the stabilization of resources and terrains can reduce the strength of environmental ltering, and the most competitive taxa may replace the least competitive ones. Such substitutions are likely driven by biotic interactions, either because early arrivers modify the environment making the conditions suitable for other colonizers but less suitable for them 1 or because later successional species exploit similar resources and outcompete the already established early species 47 . ...
Mechanisms underlying plant succession remain highly debated. A global quantification of the relative importance of species addition versus replacement is lacking due to the local scope of most studies. We quantified their role in the variation of plant communities colonizing the forelands of 46 retreating glaciers distributed worldwide, using both environmental DNA and traditional surveys. Both mechanisms concur in determining community changes over time but their relative importance varied over time along successions. Taxa addition predominated immediately after glacier retreat, as expected in harsh environments, while replacement became more important for late-successional communities. Those changes were aligned with total beta-diversity changes, which were larger between early successional communities than between late-successional communities (>50 years since glacier retreat). Despite the complexity of community assembly over plant succession, our global pattern suggests a generalized shift from the dominance of facilitation and/or stochastic processes in early successional communities to a predominance of competition later on.
... These factors may have negatively affected the richness of regenerating plants. Whilst evaluating the facilitative effects of Poincianella microphyla (another Caatinga species), Paterno et al. (2016) recorded increased germination of other tree species under its canopy. However, amongst the five species sowed under the canopy, only two of them had increased establishment. ...
... Although early successional tree species have increased nutrient availability in the soil, competition for water can also prevail (Ludwig et al. 2004;Mikola et al. 2018). Paterno et al. (2016) found that germination increased, but establishment was poor, under the canopy of M. tenuiflora, with only one of the five occurring species showing increased establishment. ...
In environments with water and nutrient constraints, some early successional shrub/tree species may promote facilitation by ameliorating the microclimate and increasing resource availability. We ask whether early successional semi‐arid shrub/tree species have facilitation effects for other woody species and if they do, which mechanisms are involved and how they affect the water status of juvenile plants. Three early successional woody species; Combretum leprosum, Cenostigma bracteosum and Mimosa tenuiflora, were chosen for investigation. The richness of regenerating woody species and their leaf water potential were used as response variables, while air and soil temperature, leaf area index, humidity and soil attributes were used as explanatory environmental variables. Species growing under the canopy of C. leprosum had better water status and growth at higher soil moisture and lower thermal and solar radiation stress, receiving a facilitative effect. The lower leaf area index, higher radiation and more negative soil water content under the canopy of C. bracteosum in comparison to C. leprosum may have a small negative effect on species richness. M. tenuiflora did not reduce environmental stress, and the species associated with it had low water potential, thus no increase in species richness was detected under its canopy. C. leprosum and C. bracteosum improve the environmental conditions under their canopies and provide favourable microsites for the establishment of other species. The positive effects may be generated by functional traits that modify microclimatic characteristics under the nurse species' canopy and lead to a higher water status of the juveniles growing under it.
... The outcome of plant-plant interactions not only will depend on community (forest stand-level) factors, but also on the identity of the newly recruiting species, as their specific competitive ability and functional strategies could condition these interactions (Schöb et al., 2013;Soliveres et al., 2015;Paterno et al., 2016;Morcillo et al., 2019a). In this sense, drought-tolerant shrubs may respond more negatively to pine competition than shade-tolerant species (e.g., Valiente-Banuet et al., 2006;Butterfield and Briggs, 2011). ...
... Previous synthesis highlighted the importance of exploring plant-plant interactions across ontogenetic stages since the balance between the positive and negative components of interactions often shifts as plants age (Brooker et al., 2008;Filazzola and Lortie, 2014). Many studies show that the effect of neighboring plants is not static and may change from facilitative to neutral or net competitive as a plant develops through life-history stages (Reisman-Berman, 2007;Armas and Pugnaire, 2009;Paterno et al., 2016;Urza et al., 2019). This pattern likely reflects the fact that larger plants usually have higher resource requirements and lower sensitivity to abiotic extremes (Niinemets, 2010), reducing the benefits of environmental stress amelioration by neighboring plants and increasing their competitive effects. ...
Monospecific pine forests are widespread due to extensive afforestation efforts and natural colonization of abandoned croplands in the Mediterranean Basin. It was originally thought that pines would facilitate the natural colonization of native late-successional resprouter species (e.g., hardwoods), but these species can be compromised if competition with pines outweighs their facilitative effect on these hardwood species. Managing the density or canopy cover of these widespread pine forests can potentially provide some "optimum" balance between facilitation and competition to maximize success in the introduction of late successional species while maintaining a tree stratum. We tested the response (survival and growth across 10 years) of six resprouter species covering a wide range of plant functional strategies, from drought-tolerant sclerophyllous shrubs and trees to malacophyllous drought-sensitive trees, across an experimental gradient of Aleppo pine canopy cover. Seedling performance varied according to the functional strategy, pine cover and time. High pine cover generally enhanced seedling survival, whereas moderate pine cover generally enhanced seedling growth, although this response was modulated by the functional strategy of the seedling species. Interactions between pines and seedlings were only detectable 2-3 years after plantation, increasing in intensity with time. The latter highlights the need of medium to long-term studies to evaluate plant-plant interactions in these water-limited environments with slow successional trajectories. Our results could be attributed to the shade tolerance of most of the introduced trees, combined with their low tolerance to the combination of high sunlight radiation and drought. We found an optimal pine cover of ca. 50% (equivalent to 300-400 trees/ha) in which both survival and growth of late successional species can be maximized, which help to select best locations for more efficient reforestation programs and set a threshold value to decide whether or not to perform tree thinning to enhance ecosystem diversity and, subsequently, resilience.
... In this sense, previous studies have found conflicts or shifts from facilitation to inhibition of sequential life stages in single nurse-beneficiary species pairs (Castanho et al., 2015;Fujita & Yamashina, 2018;Loayza et al., 2017). However, rigorous evaluations of such conflicts throughout several early life stages at the plant-community level are scarce (Bruno et al., 2017;Paterno et al., 2016;Schiffers & Tielbörger, 2006). Even less common are studies that investigate how the nature of these plant-plant interactions changes among interacting individuals (but see Anthelme et al., 2017). ...
... jacent open spaces (i.e., 'controls'), respectively (Paterno et al., 2016). ...
Question
Nurse–beneficiary plant interactions are often used to restore degraded habitats. However, whether and how shifts in plant–plant interactions along the facilitation–competition continuum alter revegetation success has been seldom considered. To test whether and how shifts in plant–plant interactions (due to woody species identity, study site, early life stage, and individual nurse) might alter plant recruitment and thus the success of revegetation projects, we chose a system comprising the Mediterranean dwarf palm ( Chamaerops humilis ) and seven common woody plant species.
Location
Two human‐degraded sites within Doñana National Park (southwestern Spain).
Methods
We carried out several well‐replicated field experiments to compare plant performance (seed survival, seedling emergence, seedling survival, seedling recruitment) in the presence and absence of Chamaerops humilis .
Results
Chamaerops humilis had marked effects on the performance of woody species that, however, changed among life stages. Depending on woody species identity, seed survival was up to 193 times greater in adjacent open spaces than beneath Chamaerops humilis . Conversely, seedling survival and recruitment were up to 19 times greater beneath Chamaerops humilis than in open spaces. Importantly, none of the studied woody species showed greater accumulated recruitment in open spaces than beneath Chamaerops humilis . Interestingly, we found strong inter‐individual palm variation in the sign and strength of their effect on woody plant performance.
Conclusions
We found strong seed–seedling conflicts the strength of which was species‐specific. The strong inter‐individual palm variation depicts a facilitation–competition continuum with important implications for restoration. We propose several management recommendations across different hierarchical levels (i.e., from individuals to communities) that may increase plant recruitment and therefore the success of revegetation projects. Our results are particularly relevant for restoring arid, semi‐arid and alpine landscapes worldwide where the nurse–beneficiary plant interactions are critical to ameliorating stressful conditions.
... Facilitation by nurse plants has been widely reported in degraded ecosystems (Gomez-Aparicio et al. 2004;Padilla and Pugnaire 2006;Arredondo-Núñez et al. 2009;Navarro-Cano et al. 2018). However, nursetarget interactions can be species-specific (Callaway 1998;Paterno et al. 2016) where a given nurse species might facilitate or compete with different target species depending on their ecological strategies and tolerance to stress (Liancourt et al. 2005;Maestre et al. 2009). Some studies have shown that nurse-plant effects occurs only when conditions are not optimal for target species (Liancourt et al. 2005;Gross et al. 2010;He et al. 2016). ...
... Besides acid-tolerance, however, other plant traits of a plant species (e.g. canopy trait, root symbiosis) might also affect the outcome of interactions between nurse plants and target plants (Paterno et al., 2016;van der Heijden 2004). It is well known that AMF affect plantplant interactions through mycorrhizal networks (Booth 2004;Booth and Hoeksema 2010). ...
Aims
We tested whether a nurse-plant effect depends on target-seedling tolerance to soil acidity and arbuscular mycorrhizal fungi (AMF) in an acid soil.
Methods
A mesocosm experiment was used to assess the acid-tolerance of the seedlings of four target species. Field experiment 1 tested the nurse effects of an adult plant (Lespedeza formosa) on germination rate, seedling survival rate, growth and AMF colonization rate of target seedlings growing in an acid soil. Field experiment 2 tested the influence of AMF root colonization on nurse-plant effects.
Results
Target species greatly varied in their tolerance to soil acidity while nurse-effect on target species were mediated by target species acid-tolerance and AMF root colonization. In field experiment 1, as expected, nurse-effect was positive for acid-sensitive species and negative for acid-tolerant species. While nurse plant presence facilitated the germination, survival, growth, and AMF colonization of the two acid-sensitive species it competed with the two acid-tolerant species. In field experiment 2, the nurse plant facilitated the growth of the acid-sensitive seedlings more under AMF not suppressed treatment than AMF suppressed treatment. For the acid-tolerant seedlings, however, the nurse plant reduced their growth under AMF not suppressed treatment, but did not affect their growth under AMF suppressed treatment.
Conclusion
Nurse plant facilitated the acid-sensitive species in an acid soil, and the facilitation was enhanced by increasing AMF in the soil. These findings highlight how acid-tolerance of target species and AMF colonization mediates nurse plant facilitation and has important implications for the use of nurse plants in the restoration of acid soils ecosystems.
... The distinctive traits of different pioneer species can influence community assembly and natural succession processes after disturbance (HilleRisLambers et al. 2012;Paterno et al. 2016). For example, the biotic influence of pioneers is evident in the different forest successions occurring beneath Kunzea spp. 1 (Myrtaceae), a group of New Zealand native pioneers, compared with those beneath Ulex europaeus (Fabaceae), a non-native invasive nitrogen-fixing shrub in the same landscapes in New Zealand (Sullivan et al. 2007). ...
... In considering early successional communities, one of the key questions is how different compositions are influenced by the original local site conditions or by the dominant pioneer. The influence of dominant pioneer species on the availability of seedling sites may have long-term effects on the composition of vegetation communities (Sullivan et al. 2007;Burton et al. 2011;Paterno et al. 2016). We suggest that New Zealand pioneers, both native and exotic, do influence the regeneration niche of potential forest dominants, by layering a biotic filter on the original heterogeneity in the landscape (Grubb 1977;HilleRisLambers et al. 2012). ...
Cyathea medullaris (Cyatheaceae) is a frequent pioneer of disturbed areas (e.g. landslides) or edge environments, sometimes forming near continuous canopies. We test the hypothesis that colonisation by this species as a pioneer alters the seedling assemblage to favour more shade-tolerant broadleaved trees than that beneath another common native pioneer (Kunzea robusta, Myrtaceae) in the same landscapes. We compared vegetation and abiotic characteristics of 166 sites across the Auckland region where C. medullaris or K. robusta were abundant (≥20% basal area) along successional gradients. Using hierarchical classification and ordination, we identified distinct communities associated with the different pioneers. In the forests we consider, C. dealbata is another common understorey tree fern, which sometimes, but not always, co-occurs with C. medullaris. Cyathea medullaris / C. dealbata successions occurred on steep sites with lower annual water deficit whereas K. robusta / C. dealbata successions were located on flatter, drier sites. The prevalence of macro-charcoal in K. robusta / C. dealbata forest suggests the prominence of that community is in part an outcome of the increased importance of fire disturbance in New Zealand. Dominance of C. medullaris, with C. dealbata understoreys, influences community assembly of tree species towards dominance by shade-tolerant species, whereas seedlings of less shade-tolerant small-leaved species are more prevalent in K. robusta / C. dealbata forests. We provide evidence to suggest that, where present in early forest communities, high tree fern abundance influences the assembly of seedling communities, supporting our hypothesis. Contrary to previous suggestions, a high abundance or basal area of tree ferns on sites not historically affected by fire did not limit the establishment and growth of canopy trees including fleshy-fruited broadleaf species.
... Facilitation is an important determinant of the structure of local communities, particularly in regions with severe climates, such as arid and semiarid regions (Cavieres et al. 2016, Fagundes et al. 2022). In the facilitation process, plant species generally called 'nurse plants' alter the conditions and/or the availability of resources in their neighbourhood, which can enhance the establishment, growth, and survival of co-occurring plant species, raising local diversity as a result (Paterno et al. 2016, Fagundes et al. 2018). This process can impact the species diversity of higher trophic levels since, with increased plant establishment success, local conditions are altered, such as microclimate, resource availability and soil conditions, which may consequently favour a larger set of species to meet their resource demands (Arnan et al. 2006, Meloni andMartinez 2021). ...
The global loss of plant diversity is expected to have reverberating effects on other trophic levels, affecting the structure and functioning of ecosystems. To understand such effects, biodiversity-ecosystem function (BEF) experiments that manipulate tree diversity have been established around the world. In a BEF experiment carried out since 2016 in a seasonally dry tropical forest, we examined the effects of tree diversity, facilitation and density of trees with extrafloral nectaries on the abundance, richness, functional diversity and phylogenetic diversity of ground ants. Also, we used artificial seeds to test seed dispersal efficiency of ants within the experiment. Generalized linear mixed models (GLMM) showed that tree richness positively affects ant abundance , richness, functional diversity and phylogenetic diversity. Also, tree richness had a strong positive effect on the proportion of dispersed seeds, as well as their dispersal distance. Contrary to our expectations, facilitation and the number of trees with extra-floral nectaries did not affect ground ants and their functions. Our results indicate that the global impoverishment of tree communities can affect several dimensions of ant diversity and their ecosystem functions, including forest regeneration processes.
... In conclusion, the single overarching finding of our study is that early successional species are important in accruing forest diversity and provisioning forest ecosystem functions. Although many of early successional species are transient in succession, they are an inherent component of forest diversity and play critical functional roles including ameliorating habitat condition thorough nutrient input and cycling, nursing later successional species, and supporting pollination (Finegan, 1984;Taki et al., 2013;Paterno et al., 2016;Eckerter et al., 2021). These highlight the conservation value of secondary forests and the importance of maintaining a mosaic of forests comprising stands of different age classes for conserving biodiversity in landscapes. ...
... Ex G. Don) E. Gagnon & GP Lewis (Fabaceae). C. microphyllum is also considered a nurse species because it facilitates the germination of surrounding plants, making it possible to restructure plant communities in areas of succession (Paterno et al., 2016). C. microphyllum was selected for this study because it is abundant across families found in Caatinga. ...
Reforestation dry tropical forests (DTF) has several challenges that need to be overcome. In this perspective, this study evaluated the performance of Cenostigma microphyllum seedlings inoculated with arbuscular mycorrhizal fungi (AMF plants) for 2 years after transplanting to the field with different rainfall intensity. AMF plants showed the highest gs values in both plots. These plants in wet plots stored more soluble sugars in their stems and roots, whereas root tissue was chosen under the dry plot. AMF plants had more phosphorus than Control plants in dry plots. Furthermore, AMF plants were 24% and 27% larger than Control plants in wet and dry plots, respectively. AMF plants root diameter was 25% and 18% greater in wet and dry plots, respectively, than in the control plants. Thus, the AMF plants showed higher main root biomass in both plots than the Control plants. The results of this study confirm that inoculation of C. microphyllum seedlings during germination confers a physiological advantage to these plants in field conditions after transplanting, regardless of water availability in the plot, even after two dry seasons. This can be a useful tool for recovering deforested areas in DTF.
... Furthermore, positive plantplant interactions are more frequent when phylogenetically distant species are co-occurring in the same community (Valiente-Banuet & Verdú, 2007;Verdú et al., 2012; but see Mayfield & Levine, 2010). This should increase survival of such species, especially when considering plants from harsh environments (Brooker et al., 2008;Carrión et al., 2017;Paterno, Siqueira Filho & Ganade, 2016). Therefore, the phylogenetic relatedness among species can be one of the aspects determining the outcomes of ecological succession during restoration of degraded areas (Verdú, Gómez-Aparicio & Valiente-Banuet, 2012;Winter, Devictor & Schweiger, 2013). ...
1. Little attention has been paid to phylogenetic diversity during restoration initiatives. Because plant phylogenetic distance can be a surrogate for functional diversity, its consideration could foster the restoration of degraded areas.
2. This study investigates the influence of species richness and phylogenetic relatedness during early restoration of a riparian forest located between the Atlantic Forest and semi-arid ecosystems in NE Brazil. The restoration experiment was established along a perennial stream in Monte Alegre, RN, investigating the significance of species richness and phylogenetic diversity for sapling survival and growth of the restored communities.
3. We used phylogenetic information on 47 tree species naturally occurring at the study site. The resulting phylogenetic tree had a basal node with three major clades. To implement the experiment, three species from each clade were randomly selected, resulting in nine species (from five families). We defined five levels of diversity: (i) no planting, (ii) monoculture, (iii) three phylogenetically related species (same clade), (iv) three phylogenetically distant species (different clades) and (v) nine species. The experiment consisted of 96 (12 m × 10 m) plots established along the two margins of the stream. Overall, 1656 saplings (20-50 cm) were planted in September 2015 (184 per species). We tested whether the survival and growth of saplings are influenced by the number of species planted and phylogenetic distance among them.
4. We assessed plant mortality and growth during two consecutive years (2016 and 2017). Survival was lower but relative growth was higher for plants near the stream. After controlling for differences in initial size, plots with phylogenetically distant species produced significantly taller plants, but only when occurring near the stream. Diversity treatments did not influence plant survival, while initial size determined plant survival and growth.
5. Our findings show that greater phylogenetic distance led to increased plant growth, probably, because of the presence of functionally divergent species that This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
... This suggests that some mechanisms that operate during ontogeny increase the mortality of more different neighbours. Several studies have found evidence suggesting shifts in plant-plant interactions from facilitation at the sapling stage to competition at the adult stage (Miriti 2006, Armas and Pugnaire 2009, Paterno et al. 2016). However, this ontogenetic shift has mostly resulted in phylogenetic overdispersion rather than clustering (Valiente-Banuet and Verdú 2008). ...
The analysis of the spatial phylogenetic and phenotypic structure of plant communities can provide insight into the underlying processes and interactions governing their assembly, and how these may change during plant ontogeny. We used point pattern analysis to find out if saplings and adult plants are surrounded by phylogenetically and phenotypically more similar or more dissimilar neighbours than expected by chance, and whether these associations change from the sapling to the adult stage. To this end, we combined information on the phylogenetic structure and eight phenotypic traits of 15 woody plant species in two Mediterranean mixed forests of southeastern Spain. At the community level, we found that the sapling bank at both sites did not show phylogenetic or phenotypic spatial patterns, but adults showed phylogenetic clustering (i.e. heterospecific neighbours were more similar than expected). At the species level, we found frequently repulsive patterns in the sapling bank of less abundant species (i.e. heterospecific sapling or adult neighbours were more dissimilar than expected) in both, phylogenetic and phenotypic analyses. For the adult stage, we found phylogenetic attraction (i.e. more similar neighbours) in just one species and phenotypic clustering in four species. The processes driving the assembly of the communities of saplings and adults leave detectable signals in the spatial phylogenetic and phenotypic structure of our two forest communities. Our findings reinforce the existence of ontogenetic shifts in the mechanisms involved in plant community assembly. Facilitation between phylogenetically distant and phenotypically divergent species favours the recruitment of less abundant species. However, processes acting later in the ontogeny ameliorate the competition between close relatives and determine the spatial structure of adult plants. Nevertheless, the role of phenotype in shaping the interactions between adult plants was context‐ and trait‐dependent. The use of spatial point pattern analysis allowed a nuanced interpretation of the phylogenetic and phenotypic structures of plant communities.
... For instance, Larrea tridentata, the dominant shrub species across our Mojave Desert sites, can be a relatively poor facilitator compared to other shrub species due to strong competitive effects and allelopathy (reviewed by Callaway, 2007), though we found limited evidence for this. A key mechanism that determines whether shrubneighbor interactions are positive or negative is the match between what the shrub offers and what the beneficiary species requires (Paterno et al., 2016). Importantly, the offerings and requirements of species depend upon their functional traits (Funk et al., 2017). ...
Positive interactions can drive the assembly of desert plant communities, but we know little about the species-specificity of positive associations between native shrubs and invasive annual species along aridity gradients. These measures are essential for explaining, predicting, and managing community-level responses to plant invasions and environmental change. Here, we measured the intensity of spatial associations among native shrubs and the annual plant community—including multiple invasive species and their native neighbors—along an aridity gradient across the Mojave and San Joaquin Deserts, United States. Along the gradient, we sampled the abundance and species richness of invasive and native annual species using 180 pairs of shrub and open microsites. Across the gradient, the invasive annuals Bromus madritensis ssp. rubens (B. rubens), B. tectorum, B. diandrus, Hordeum murinum, and Brassica tournefortii were consistently more abundant under shrubs than away from shrubs, suggesting positive effects of shrubs on these species. In contrast, abundance of the invasive annual Schismus spp. was greater away from shrubs than under shrubs, suggesting negative effects of shrubs on this species. Similarly, native annual abundance (pooled) and native species richness were greater away from shrubs than under shrubs. Shrub-annual associations were not influenced by shrub size or aridity. Interestingly, we found correlative evidence that B. rubens reduced native abundance (pooled), native species richness, and exotic abundance (pooled) under, but not away from shrubs. We conclude that native shrubs have considerable potential to directly (by increasing invader abundance) and indirectly (by increasing negative impacts of invaders on neighbors) facilitate plant invasions along broad environmental gradients, but these effects may depend more upon invader identity than environmental severity.
... We argue that the combination of these factors may have contributed to the differences found in the structure of the studied plant communities. On the other hand, there are reports of species-specific negative effects between ontogeny of nurse species and the development of target species (Paterno et al., 2016;Fagundes et al., 2018). Therefore, future studies need to focus on the understanding of which environmental parameters and which traits of each species would be improved under the influence of the nurse species B. dracunculifolia. ...
The introduction of nurse species on degraded sites of Permanently Protected Areas represents a useful strategy for vegetation recovery in riparian forest. Species of the genus Baccharis (Asteraceae) have been documented as potential nurse plants being able of restructuring the native plant community. This study was aimed to evaluate the potential nursing role of Baccharis dracunculifolia in the recovery of a native plant community of a degraded Atlantic rainforest in a short-time period. The study was developed in two abandoned pasture areas in a riparian forest in the River Piranga basin, one in which B. dracunculifolia was planted (Restored treatment) to promote restoration, and a second area with no intervention (Degraded = Control treatment). Sampling took place 18 months after the planting of B. dracunculifolia. We set up 20 plots of 2 × 2 m in each treatment type (n = 40 plots), where all plant species were recorded (with the exception of the introduced Baccharis individuals and grasses), classifying them as native, ruderal, or alien. Plant richness was twice higher in the Restored treatment than the Degraded treatment. Furthermore, the observed values of alpha, gamma and beta diversity were also higher in Restored treatment. Restored treatment had 17 exclusive native species, while the Degraded treatment had only three non-exclusive native species. In addition, fewer ruderal and alien species were recorded in the restored plots with B. dracunculifolia compared to degraded plots. We concluded that, even in a short time period, planting B. dracunculifolia had a positive effect on promoting the assembly of the native plant community and possibly decreasing the chances of invasion by alien species.
... Evaluation of dynamics of plant and soil properties can offer more details on ecosystem stability and sustainability, thereby contribute to predict the successional trajectory induced by grazing practices (Tang et al., 2010;Paterno et al., 2016;Shi et al., 2018). ...
Most alpine meadow on the Tibetan Plateau are at different stages of community succession induced by grazing practices. Quantifying the succession sequence and assessing the dynamics of plant composition, ecosystem coupling, and multifunctionality across successional stages are essential for reasonable restoration of degraded alpine meadow. Here, we selected areas with different grazing disturbance histories and used them as a space series (i.e., space-for-time substitution) to study the community succession. Our work quantified the plant succession sequence of alpine meadow induced by grazing with plant functional group approach. The plant succession sequence is from the tall sedge community with erect growth to the short undesirable toxic forbs community with prostrate growth. Ecosystem coupling, ecosystem multifunctionality and their relationships were all the lowest in Stage 4. Compared to Stage 4, the ecosystem multifunctionality index increased in Stages 1, 2, and 3 by 102.6, 89.8, and 207.6%, respectively; the extent of ecosystem coupling increased by 20.0, 16.8, and 21.2%, respectively. Our results indicated that the driving factors of ecosystem coupling and ecosystem multifunctionality were soil factor individual in early successional stage to plant-soil simultaneously in late successional stage. Our results also highlighted the importance of toxic weeds during the late stage of degraded succession and suggest that the expansion of toxic plants is a consequence of their greater suitability from a successional perspective. The findings of this study would provide valuable guidance for optimizing the management and restoration practice of alpine meadow.
... For example, native trees can maintain water availability, and reduce soil temperature through shading underneath their crown. This mechanism can further drive changes in community structure, increasing species diversity (Flores & Jurado 2003;Cavieres & Badano 2009;Paterno et al. 2016). Conversely, herbaceous vegetation can inhibit tree establishment and seedling growth due to strong competition for water, light, space, and nutrients (Callaway & Walker 1997;Davis et al. 1998;Maestre et al. 2003;Vandenberghe et al. 2006;Gomez-Aparicio 2009;Maestre et al. 2009). ...
We evaluated the influence of herbaceous vegetation on the colonization of an invasive and two native tree species in a degraded area located at the Caatinga semiarid forest in Northeastern Brazil. Seedlings of the native trees Anadenanthera colubrina and Astronium urundeuva were planted in nine paired blocks with intact and removed herbaceous vegetation. Additionally, seeds of the invasive tree species Leucaena leucocephala were sown in the same paired plots. Growth, germination, establishment and survival of the tree species were monitored for eight months. The results showed that herbaceous vegetation hampered native seedling growth in respect to leaf number, leaf size, height, and stem diameter. Conversely, herbaceous vegetation had a neutral effect on the germination, establishment, and growth of the invasive species Leucaena leucocephala. Dominant ruderal herbaceous species strongly prevent the natural succession of native trees in this semiarid forest, while not affecting the establishment of an invasive tree. Management of herbaceous vegetation cover in degraded areas might be a key step for successful restoration in this dryland.
This article is protected by copyright. All rights reserved.
... As the plant grows, there is an exponential increase in body size, leading to modifications in the strategies of water, nutrients, and carbohydrates transport, and communication between tissues (Day and Greenwood 2011). In addition to physiological changes, ecological and structural changes modify competitive capacities and vulnerability to predators and pathogens (Miller and Rudolf 2011), characterizing changes of the ontogenetic niche (Paterno et al. 2016). Juvenile plant individuals live in the understory of the forest, and therefore, are shaded by adult trees, thus, experiencing a strong competition for light (Kitajima and Poorter 2008) affecting survival of individuals. ...
Key message
The allometric relationships of tropical trees change along ontogeny and ecological succession at the level of populations and communities.
Abstract
Tree size and shape can influence their survival and growth, affecting the community dynamics. In this study, we explored how the tree allometric relationship is altered along in the succession of a tropical forest. We measure stem diameter (SD), total height (H), crown volume (CV) of juvenile, and adult trees in areas of 7–17, 20–30, 35–55, and > 80 years of Atlantic Forest in Brazil. The study was carried out for the community (all individuals were considered) and population (the most abundant species). We tested allometric relationships between H, SD and CV with the standardized major axis function. The results indicate that, in general, successional gradient establishes conditions that affect the way resources are invested in trees, despite variations among the type of allometric relationship, the ontogenetic phase, the successional stage and species considered. There are tendencies in individuals becoming taller, and proportionally, with crowns less voluminous along the succession. Variations in height, stem diameter and crown investment along the successional gradient suggest that shade tolerance is the main driver affecting the ontogenetic niche and shaping tree allometry. These results suggest that the successional age and the ontogeny of the individuals affect plant dynamics, and possibly, the coexistence of the species.
... While in the later stage of fencing, the competition among species caused some species to withdraw from the community and dominant species tended to be in a state of minority and concentration. At the same time, soil resources can improve the survival rate of late-stage species in succession and thus change the succession of vegetation (Paterno et al. 2016;Song et al. 2019). ...
AimsBelowground carbon (C) input is a key component of the global C cycle. However, how does fencing affect Belowground net primary production (BNPP) and the contribution of root derived C to belowground C input remains poorly studied.Methods
In this study, the in-growth soil cores-13C method was used to quantify net root C input. Five different plant communities of different fencing years (1 year, 5 years, 10 years, 25 years, 30 years) in the Loess Plateau of China, characterized by herbs and shrubs were investigated.ResultsBNPP was increased with the increase of fencing years: 61.54~140.23 gC·m− 2·yr− 1. Root derived C in soil represented a considerable contribution to BNPP varying from 57 to 81 %, and the proportion of root derived C to BNPP was decreased with the fencing years. The contribution of root derived C to soil organic carbon (SOC) was 3 %~5 % during one-year growth.Conclusions
Our results underline the fact that fencing is an effective means to improve the BNPP and plant community. Root derived C rather than root biomass contributes to the SOC sequestration in grassland soils with different fencing years. Fencing increases the contribution of root derived C to SOC mainly by increasing root C content.
... Plant interactions, including competition and facilitation, are a complex phenomenon that are becoming increasingly unpredictable under climatic change (Ploughe et al. 2019). Recent studies reveal that plant interactions are highly dynamic, shifting from facilitative to competitive and back again as both resource availability and plant growth strategies change over time (Armas & Pugnaire 2005;Grant et al. 2014;Wright et al. 2015;Paterno et al. 2016). Experiments with Pinus palustris, demonstrate that although drought and invasive species suppressed the native tree species, the invader temporarily moderated stressful drought conditions, and at least some Pinus trees were able to survive despite increasingly strong competition (Alba et al. 2019). ...
Amazon wetlands are among the most vulnerable ecosystem to be impacted by climate change, which may increase the frequency of extreme droughts and floods. We used Eichhornia crassipes and Pistia stratiotes, two abundant aquatic plants in the Amazon floodplains, to evaluate the effects of combined temperature and [CO2] increase on growth, physiology and ecological interactions. Individual and paired plants were deposited for three weeks in a microcosm under four IPCC scenarios: control (current temperature/CO2), mild (control + 1.5 ºC, 200 ppm CO2), intermediate (control + 2.5 ºC, 450 ppm CO2) and extreme (control + 3.5 ºC, 850 ppm CO2). P. stratiotes died after three weeks in the intermediate and extreme treatments; E. crassipes experienced no mortality or change in any of the measured variables during the same period. P. stratiotes reduced root length in the mild treatment and reduced total dry biomass in intermediate and extreme treatments, revealing less tolerance to climate change. Ecological interactions between the two species changed with increasing [CO2] and temperature neutral interaction changed to facilitation for E. crassipes, while competitive interaction changed to neutral for P. stratiotes. Global climate change may alter the composition, biomass and ecological interactions of Amazonian aquatic plant species.
... FLORESTA,Curitiba,PR,v. 51,n. 1, Water is a limiting factor for areas in initial successional stages, favoring the emergence of more robust and tolerant species. However, as succession progresses, shading becomes a protagonist, protecting emerging species with a low stress tolerance to water deficiency (PATERNO et al., 2016). ...
Studying selected floristic changes in dry forests is fundamental to foster conservation and sustainability strategies. Objective: to analyze the occurrence of woody species in a tropical forest with a history of use. In 2008, 40 permanent plots were installed and wood with a circumference of 1.30 m at a breast height (CAP) ≥ 6 cm were measured. In 2012, newly established individuals (those that did not meet the size requirements in 2008 but did in 2012) and mortality of the remaining individuals were analyzed by computer. Where applicable, the density, frequency, and absolute dominance, importance value, newly established individuals, mortality, and gross growth for each species, along with the Shannon index were estimated. The floristic composition and diversity remain unchanged. After four years, there were few differences between species, while in most cases the growth in the basal area was positive and sometimes the number of newly established individuals exceeded the mortality. After 24 years of logging, the analyzed forest area did not reach its initial basal area stock when compared to other areas of the Caatinga that do not have a history of disturbance.
... Studies focusing exclusively on the recruitment stage cannot discard that facilitation shifts to competition when facilitated plants grow up (Tielb€ orger and Kadmon, 2000). In fact, evidence exists pointing to several directions, with initial positive nurse effects on seedlings reverting to negative (Miriti, 2006), neutral (Urza et al., 2019) or remaining positive (Paterno et al., 2016) on adults. Phylogenetically informed facilitation networks between adult nurses and facilitated species have helped testing whether initial facilitation interactions persist over time Verd u et al., 2010). ...
Identifying the plant traits that determine the outcome of facilitation interactions is essential to understand how communities are assembled and can be restored. Plant facilitation networks are phylogenetically structured but which traits are behind such a pattern is unknown. We sampled plant interactions in stressful ecosystems from south‐eastern Spain to build seedling and adult facilitation networks. We collected 20 morphological and ecophysiological traits for 151 species involved in interactions between 879 nurse individuals benefiting 24 584 seedlings and adults. We detected a significant phenotypic signal in the seedling facilitation network that was maintained in the adult network, whereby functionally similar nurses tended to facilitate functionally similar species whose traits differ from those of their nurses. We provide empirical evidence to support a long‐lasting theoretical postulate stating that facilitation networks are phenotypically structured. Trait matching through which nurse and facilitated species avoid phenotypic overlap, and consequently competition, is the main linkage rule shaping plant facilitation networks.
... The nursing plants benefit the growth of seedlings because of the reduction of stressful factors, both biotic (as herbivory) and abiotic (as high temperature, reducing evapotranspiration, and increasing nutrients in soil) (MOURA; MALHADO;LADLE, 2013;CARRIÓN et al., 2017). Literature reported that seedlings from some species are only founded under the canopy of nursing plants (PATERNO; SIQUEI-RA-FILHO; GANADE, 2016;CARRIÓN et al., 2017). Competition for water in seasonal dry forest may affect growth, but relation benefits-competition depends on species and their ontogeny (TROVÃO; FREIRE; MELO, 2010). ...
Faltam informações básicas sobre as florestas de galeria da Caatinga. Os objetivos do estudo foram obter informações básicas da floresta de galeria do Pajeú (Pernambuco, Brasil) e oferecer diferentes maneiras de restaurá-las e conservá-las. Foi realizada a caracterização do estado de conservação e seu banco de sementes. A caracterização foi feita usando um índice de qualidade (índice QBR) e uma avaliação do uso do solo por meio de imagens de satélite. Em seguida, foi realizado um inventário sobre as plantas nativas das matas ciliares da caatinga, a fim de testar métodos ativos de restauração no campo. Para isso, foi construída uma análise multicritério que incluiu todas as espécies de árvores e arbustos, com base em pesquisas prévias locais e citadas na literatura. Após essa análise, algumas espécies foram cultivadas em um viveiro de plantas para testar sua germinação, sobrevivência e taxas ALde crescimento para diferentes solos e frequências de irrigação. Finalmente, o transplante na floresta de galeria foi avaliado mediante a observação das taxas de sobrevivência e crescimento de diferentes espécies nativas que foram plantadas diretamente na floresta. Nossos resultados mostram que o QBR global foi de 43,73 e que 73% das terras tinham qualidade insuficiente (64%) ou ruim (9%), no entanto algumas áreas mantiveram alta biodiversidade. Foram observadas 23.651 sementes germinadas no banco de sementes, em que a maioria das germinações (53%) veiodo local preservado. Os solos recolhidos durante a estação seca também ofereceram mais plântulas (60%) do que os seus homólogos da estação chuvosa (40%). Quanto à restauração ativa, observou-se que algumas plantas são mais adequadas para viveiros e transplantes de árvores como Sapindus saponaria, Vitex gardneriana e Celtis iguanaea e que, selecionando as plantas e técnicas corretas, o ecossistema pode ser restaurado. Há ainda um longo caminho para a restauração da floresta de galeria do Pajeú. Estudos como este são essenciais para aumentar o conhecimento desse ecossistema. Esta pesquisa servirá como referência para orientar estratégias de manejo/restauração, priorizando ações e o desenvolvimento de políticas públicas de conservação a longo termo que garantam a integridade do ecossistema e suas funções.
... It is a species that tolerates droughts well, with a large annual regrowth capacity, and is used as an energy source due to the excellent quality of the wood. In addition, it can favor the regeneration of plants that grow under its canopy, thus contributing to the regeneration of eroded soils, as well as being indicated for ecological restoration programs (Santos et al., 2011, Paterno et al., 2016. ...
This research aimed to evaluate the physiological responses of Mimosa tenuiflora plants submitted to variable water availability conditions during the nursery stage. Twelve-month-old plants kept in plastic pots containing 5 kg of the substrate composed of the subsoil soil mixture and bovine manure (2:1) were submitted to two treatments: irrigated (control) and water stress, which was imposed through the suspension of irrigation, rewatering after seven days of stress. The relative water content (RWC) and stomatal parameters were evaluated. The M. tenuiflora plants responded quickly to the irrigation suspension, promoting the closure of the stomata, occurring reduction in stomatal conductance, transpiration rate and photosynthesis. The instantaneous efficiency in water use of plants under water deficit remained high only until the middle of the period when irrigation was suspended, and then declined until the last day of the water deficit. After rehydration, the plants showed recovery in all evaluated parameters, indicating that the level of stress imposed did not cause irreversible damages in the cells and tissues.
... The wood is widely used in construction and as fuel, whereas the bark and flowers are used in traditional medicine for stomach ailments (Queiroz 2009). It is a nurse species, which favors the germination and the establishment of seedlings that grow under its canopy, thus creating positive interplant interactions (Paterno et al. 2016). ...
Seasonally tropical dry forests are among the most threatened environments by climate change. However, these forests, which are at risk of desertification, are still poorly studied and conserved. Seeds of several species endemic to the Caatinga, a Brazilian dry forest, are also understudied, mainly regarding their ability to cope with a hotter and drier climate predicted for the future. For the first time in seeds of Cenostigma microphyllum (Leguminosae), we aimed to study the presence of physical dormancy, temperature and salt tolerance to ascertain the effects of current and future climate on seed germination. Intact and scarified seeds were investigated by incubating at constant temperatures (15 to 40°C) or in NaCl solutions (−0.2 to −1.0 MPa) at 25 and 30°C. Thermal and osmotic thresholds, as well as thermal time and hydrotime constants, were calculated using linear regressions between the germination conditions and germination rate. To predict germination in the future, a heat sum model based on thermal time and hydrotime was applied to current and future climate scenarios. Seeds of C. microphyllum were permeable to water and did not have physical dormancy. The results indicated that increases in temperature are unlikely to affect germination, despite greater sensitivity to salinity presented at higher temperatures. In a future climate, the reduction in the number of weeks with at least 15 mm rainfall will affect the germination timing for the seeds. Thus, we can conclude that under the most pessimistic climate scenario predicted for the future, the seed germination of C. microphyllum may be restricted, likely leading to low seedling recruitment and establishment.
... The number of realized (among all potential) interactions, varying between 26.6% and 28% for seedlings and juveniles-adults, falls within the range observed in other plant communities shaped by facilitation (15.7%-34.7%;. We detected a remarkable variation in the extent of involvement of the nurses in the interaction network, which correlates well with the idea that a nurse species is not necessarily a good benefactor for any facilitated species(Landero & Valiente-Banuet, 2010;Paterno, Siqueira Filho, & Ganade, 2016). Instead, there is a species-specificity in the nursing effect that hampers the selection of the appropriate nurse-facilitated species pair(Lortie, 2017). ...
Traditional restoration programmes have focused on conditioning plantation sites and reintroducing plant species. Nowadays, however, ecological restoration is conceived as the complete recovery of biodiversity and ecosystem performance. Here, we review the use of plantplant facilitation as a tool to restore both diversity and ecosystem functions. Facilitation is an ecological interaction between a nurse species, which is able to colonize a stressful habitat and modify the microenvironment beneath its canopy, and the beneficiary species that are not so stresstolerant and grow under the nurse. Differences in the establishment niche between the nurse and its beneficiaries imply that species sharing facilitative interactions have different functional traits, and can therefore coexist. This process increases, at the landscape scale, all taxonomic, functional and phylogenetic plant diversity. Plant diversity patterns further permeate into those of consumers and decomposers. Thus, restoration based on plantplant facilitation allows the recovery of multiple facets of diversity at several trophic levels and, eventually, the restoration of essential ecosystem functions (fertility, productivity, or decomposition). We illustrate these cascading effects in the text by means of observational surveys in natural ecosystems governed by facilitation, as well as manipulative experiments and restoration activities.
... While facilitation has been considered important in resource-limited alpine and desert ecosystems, competition is often deemed the main structuring force in other types of plant communities (Brooker and Callaghan 1998, Craine and Dybzinski 2013, Trinder et al. 2013. However, recent studies reveal that plant interactions are highly dynamic, shifting from facilitative to competitive and back again as both resource availability and plant growth strategies change over time (Armas and Pugnaire 2005, Grant et al. 2014, Wright et al. 2015, Paterno et al. 2016. ...
Global change stressors such as drought and plant invasion can affect ecosystem structure and function via mediation of resource availability and plant competition outcomes. Yet, it remains uncertain how native plants respond to drought stress that co‐occurs with potentially novel resource conditions created by a nonnative invader. Further, there is likely to be temporal variation in competition outcomes between native and nonnative plant species depending on which resources are most limiting at a given time. Interacting stressors coupled with temporal variation make it difficult to predict how global change will impact native plant communities. To address this knowledge gap, we conducted a 5‐yr factorial field experiment to quantify how simulated drought, plant invasion (by cogongrass, Imperata cylindrica), and these stressors combined, affected resource availability (soil moisture and light) and competition dynamics between the invader and native longleaf pine (Pinus palustris), a foundation species in southeast U.S. forests. Drought and invasion mediated the survival and performance of pine seedlings in temporally dynamic and unexpected ways. Drought and invasion alone each significantly reduced pine seedling survival. However, when the stressors occurred together, the invader offset drought stress for pine seedlings by maintaining high levels of soil moisture, humidity, and shade compared to uninvaded vegetation. This facilitative effect was pronounced for 2 yr, yet shifted to strong competitive exclusion as the invasion progressed and the limiting resource switched from soil moisture to light. After 3 yr, pine tree survival was low except for pines growing with uninvaded vegetation under ambient precipitation conditions. After 5 yr, pines experiencing a single stressor were taller and had greater height to diameter ratios than pines under no stress or both stressors. This outcome revealed a filtering effect where poorly performing trees were culled under stressful conditions, especially when pines were growing with the invader. Together, these results demonstrate that although drought and invasion suppressed a foundation tree species, the invader temporarily moderated stressful drought conditions, and at least some trees were able to survive despite increasingly strong competition. Such unpredictable effects of interacting global change stressors on native plant species highlight the need for additional long‐term studies.
... The number of realized (among all potential) interactions, varying between 26.6% and 28% for seedlings and juveniles-adults, falls within the range observed in other plant communities shaped by facilitation (15.7%-34.7%;. We detected a remarkable variation in the extent of involvement of the nurses in the interaction network, which correlates well with the idea that a nurse species is not necessarily a good benefactor for any facilitated species(Landero & Valiente-Banuet, 2010;Paterno, Siqueira Filho, & Ganade, 2016). Instead, there is a species-specificity in the nursing effect that hampers the selection of the appropriate nurse-facilitated species pair(Lortie, 2017). ...
Plant facilitation, an ecological interaction that benefits at least one species without harming the other, is increasingly used as a restoration tool. To restore degraded habitats under a facilitation framework, practitioners must correctly select both the benefactor (nurse) and the beneficiary (facilitated) species.
Based on community assembly and species coexistence theory, we propose selecting plant species that largely differ in a suite of functional traits so that competition is minimized and facilitation maximized due to functional complementarity. To apply this guideline in a pilot restoration experiment performed in metalliferous mine tailings in South‐Eastern Spain, we first built the plant–plant facilitative interaction network naturally occurring in a set of 12 tailings. After characterizing each species with 20 morphological and physiological traits, we verified that facilitative interactions were predominantly established between functionally distant species.
Then, we designed a sowing experiment combining 50 nurse‐facilitated species pairs separated by a wide range of functional distances. The success of seedling establishment significantly increased with the functional distance between the nurse and the facilitated plant species.
Synthesis and applications. We encourage the use of ecological facilitation together with trait‐based species selection to design restoration programmes based on the principle of increasing functional distance between target species. This method may not only promote the restoration of the plant cover but also impact paramount ecosystem functions, thus being an efficient low‐cost restoration practice in abiotically stressful ecosystems.
... facilitative) to neutral or net negative (i.e. competitive) as a plant progresses through life-history stages (Miriti, 2006;Reisman-Berman, 2007;Valiente-Banuet & Verd u, 2008;Armas & Pugnaire, 2009;Paterno et al., 2016). This pattern likely reflects the fact that larger plants typically have greater resource requirements and lower sensitivity to abiotic extremes (Grubb, 1977;Niinemets, 2010), reducing the benefits of environmental stress amelioration by neighboring plants and increasing their competitive effects. ...
Plant–plant interactions are important drivers of ecosystem structure and function, yet predicting interaction outcomes across environmental gradients remains challenging. Understanding how interactions are affected by ontogenetic shifts in plant characteristics can provide insight into the drivers of interactions and improve our ability to anticipate ecosystem responses to environmental change.
We developed a conceptual framework of nurse shrub facilitation of tree establishment. We used a combination of field experiments and environmental measurements to test the framework with a shrub (Artemisia tridentata) and a tree (Pinus monophylla), two foundation species in a semiarid environment.
Shrub microsites allowed trees to overcome an early population bottleneck and successfully establish in areas without tree cover. Shrubs facilitated trees at multiple ontogenetic stages, but the net outcome of the interaction shifted from strongly positive to neutral after the transition of P. monophylla from juvenile to adult foliage. Microhabitat conditions varied across a broad elevational gradient, but interaction outcomes were not strongly related to elevation.
Favorable microsites provided by A. tridentata cover are crucial for P. monophylla recovery after stand‐replacing disturbance. Models of vegetation response to rapid global environmental change should incorporate the critically important role of nurse shrub interactions for ameliorating population bottlenecks in tree establishment.
... One possibility is that these shrubs may have different preferences for soil type, differ in response to past disturbance, or differ in other environmental conditions that also affect understory communities. Another possibility is that the environmental requirements and disturbance responses for these shrubs are the same, but that the shrub species differ in the types of microsite conditions they provide for understory species (Donovan and Ehleringer, 1994;Gholami et al., 2018;Paterno et al., 2016). Future work could differentiate the role that these species play, as either indicators of past change or engineers of understory and seed bank dynamics. ...
... In weed science, an overall comprehension regarding plant associations is usually ignored, but its importance lies on two aspects: (1) weed species that build up a positive association will respond better to environmental stresses, such as extreme temperatures and water stress (Paterno et al., 2016); and (2) the understanding of the association among weed species in arable fields would make possible to elaborate management strategies, whether they are chemical or not, that would control a wider range of weed species occurring simultaneously. The understanding of these two aspects would provide weed researchers with information about the species that are most prone to survive, reproduce, and increase its frequency into the community as they work together. ...
We aimed to assess the potential of the characterization of association among weed species as a tool to understand weed occurrence for further supporting long-term management programs. After a sequence of summer crops, which included irrigated rice and sorghum, the experimental area was submitted to subsoiling, limestone was applied, and ryegrass was planted in the winter season. Six months later, an ACCase-inhibitor herbicide was used to select only non-grassweed species. Field survey was carried out on 100 quadrats with 0.5-m width that were randomly sampled. Plant species were organized in 2 × 2 contingency tables. The results of the calculated chi-squares were compared to the respective tables, and results were presented as a paired chi-square matrix. The species–area curve was also obtained. The relative occurrence of species was determined by its frequency and presented as a wordcloud. The network analysis was obtained by using the Fruchterman–Reingold layout. The hypothesis of plant association aiming survival in arable fields was validated. The methodology of plant association based on the chi-square test was applicable to arable fields, where weed species (usually competitor plant types) occur in clusters. From a practical point of view, preference should be given to herbicides that are efficient on most species within a given cluster.
... Gaining advantages from neighbouring plants may increase growth opportunities over and above those gained through competitive superiority, particularly in highly stressful environments (stress gradient hypothesis: Bertness and Callaway 1994, Callaway and Walker 1997, Holmgren et al. 1997. Over the life of a plant, the relative strengths of competition and facilitation vary (Wright et al. 2014;Paterno et al. 2016) and interactions are influenced by other biotic interactions (e.g. herbivory, Hamilton III and Frank 2001). ...
Lianas are prevalent in gaps and edges of forests where they compete intensely with trees, reducing growth and recruitment. Invasive lianas have the potential to be particularly harmful as the competitive advantage of the liana life history may be coupled with the more competitive qualities of invasiveness. However, in early stages of growth of lianas and native tree seedlings, facilitatory interactions or competitive interactions associated with soil nutrients may be more prevalent. We investigated interactions at the early stages of growth between native and invasive lianas with a common rainforest tree of temperate Australian rainforests under different light conditions. Invasive lianas, as a group, were not more competitive than native lianas in reducing growth of a native rainforest seedling. At this stage in the life cycle most lianas were as competitive as a conspecific seedling. However, one invasive liana, Anredera cordifolia, was particularly competitive and reduced biomass of tree seedlings. Light had little effect on growth of lianas nor on the impact of competition, however, specific leaf area differed between low and medium light conditions. Moderate light did improve growth in the rainforest tree seedling. When lianas were grown with a rainforest tree, three liana species overyielded, while one species was unaffected by growing with the tree seedling. Overyielding suggests a strong positive interaction with the neighbouring plant, mediated through belowground processes. We discuss the potential for these interactions to be facilitative, parasitic or competitive. We therefore show that interactions early in the life of rainforest species can be complex mixtures of interactions which are likely to influence the ability of lianas to dominate rainforests.
Plant phylogeny, diversity, and production of germination inhibiting chemicals can be used as patterns for inferring key drivers of plant community construction and assembly. We conducted the study in a restoration area of Atlantic Rainforest from Southeast Brazil. In this context, we aimed to investigate community assembly rules by simultaneously evaluating the relationships of species with a phylogenetic, functional, and ecophysiological (allelopathy) approach and multifaceted β diversity (taxonomic, phylogenetic, and functional). We measured the plant canopy height and diameter at soil height for all individuals and determined successional group and dispersal syndrome for all species regenerating in open areas and below 18 adult individuals of each tree species Bixa atlantica Antar & Sano, Inga laurina (Sw.) Willd., Joannesia princeps Vell. and Senna multijuga subsp. multijuga var. verrucosa (Vogel) H.S.Irwin & Barneby. Phylogenetic and functional indexes of community structure were calculated with the net relatedness index and the nearest taxon index. Taxonomic, phylogenetic, and functional diversities (respectively, TD, PD, and FD) for the regenerating community in each area were calculated and pairwise comparisons were made for TD, FD, and PD components of β diversity. Tests of tree species allelopathy derived from leaf extract were performed with seeds of Lactuca sativa L. (Asteraceae). The effects of diversity and extracts on seed germination were analyzed using generalized linear models. The phylogenetic and functional structure of the regenerating communities under the four tree species did not differ from random for the four studied tree species. The PD was significantly higher for the communities that regenerated under Joannesia, while the FD was higher under both Joannesia and Senna, compared to communities from open sites, evidencing a facilitation mechanism for these two species. Only Senna and Inga differed from random in relation to β TD and β FD, suggesting possible environmental changes in these areas. Seeds irrigated with the extracts of Inga, Joannesia, and Senna inhibited germination in an intermediate way, whereas seeds irrigated with Bixa extract had only 1 % germination, indicating allelopathic effects. In this way, the planted species directly influence the organization of communities that regenerate below their canopies. It is therefore important to choose species that can contribute to improving diversity, and thus favor the success of restoration projects.
Background: Individual pioneer tree species often dominate early tropical dry forest succession and thereby affect possible successional pathways. Mimosa acantholoba var. eurycarpa is a highly dominant species in the tropical dry forest in Mexico. Hypothesis: Mimosa acantholoba var. eurycarpa exerts an inhibitory effect on the germination, establishment, survival, and early growth of light-demanding pioneers, while facilitating these processes for shade-tolerant old-growth forests species. Studied species: Lonchocarpus torresiorum, Lysiloma divaricatum, Mimosa acantholoba var. eurycarpa and Vachellia farnesiana. Study site and dates: Nizanda, Oaxaca, Mexico, 2020-2021. Methods: In 12 early successional plots, we applied three levels of crown cover removal (100, 50, and 0 %) of established trees of the dominant pioneer legume (M. acantholoba var. eurycarpa). We sowed seeds of the four study species in each experimental plot and recorded their germination, establishment, survival, and early growth over a 2-mo period. Results: The removal of crown cover of established M. acantholoba var. eurycarpa trees did not significantly affect germination. Lysiloma divaricatum had the highest germination probability, the fastest germination, and the highest establishment probability regardless of treatment. Lonchocarpus torresiorum had the highest establishment probability in plots where the crown cover of established M. acantholoba var. eurycarpa trees was removed The survival probability of both shade-tolerant species was highest in the 100 % removal treatment. Conclusions: Despite successful germination of shade-tolerant species, their survival is inhibited under the dense canopy of the dominant legume. Therefore, interventions to reduce the crown cover area of this dominant legume may stimulate forest recovery.
1. In carrion insect communities, facilitation and processing chain models, in which carcass feeding by early colonists facilitates colonisation by later colonists, have been regarded as the succession mechanisms without sufficient empirical evidence. Although the two models are similar, the processing chain model also assumes a facilitation process independent of early colonists.
2. To reveal the succession mechanisms, field experiments focusing on two silphids, Necrophila japonica, early colonist, and Nicrophorus concolor, later colonist, were conducted.
3. I controlled carcass feeding by Ne. japonica by introducing different numbers of them to carcasses in the field to address three questions: (i) whether the introduction promoted Ni. concolor colonisation, (ii) whether the introduction affected Ni. concolor carcass utilisation, and (iii) whether Ni. concolor colonisation affected the introduced Ne. japonica.
4. Although Ne. japonica introduction hastened colonisation by Ni. concolor, Ni. concolor colonisation did not depend on Ne. japonica, as assumed by the facilitation model because, due to normal carcass decomposition, it occurred on carcasses that Ne. japonica had not fed on, as assumed by the processing chain model.
5. Carcasses with more Ne. japonica feeding was utilised by Ni. concolor for feeding rather than reproduction. After arrival, Ni. concolor excluded Ne. japonica from carcasses.
6. These results suggested that succession between Ne. japonica and Ni. concolor may be driven by the processing chain model and interference competition.
Seasonally dry tropical forests are characterized by several months of drought. Cenostigma microphyllum is a native woody species widely found in a seasonally dry tropical forest. These forests are in need of restoration and C. microphyllum is a species that can be used to this end. We studied, 1) acute water deficiency using plant in pot, and 2) chronic water deficiency in field conditions in areas with different rainfall gradients, always with two group of plants: inoculated and non-inoculated with arbuscular mycorrhizal fungus. Acute water deficit levels in previously inoculated and non-inoculated treatments were similar, however, after rehydration, the inoculated potted plants showed faster recovery of water status and gas exchange. In field conditions, on the 120th day, before the beginning of the dry period, 100% of transplanted seedlings survived, while the total plant dry biomass did not differ between the inoculated and control groups. The same patterns emerged across rainfall gradient. After 365 days of seedling transplantation, the field survival dropped from 100% to 58%. Sixty-eight percent of the inoculated plants survived, whereas more than half of the non-inoculated individuals did not resprout at the beginning of the rainy season. Among the remaining plants, 63% were from the rainiest plots. The average of CO2 assimilation for both treatments was 2.63 and 9.43 μmol m⁻² s⁻¹ in the two driest and wettest plots, respectively. Our results suggest that artificial inoculation appears to be associated with better plant recovery or resilience following low water availability, particularly chronic/prolonged drought. Thus, the present work recommends the use of the seedling production technique, with long roots as well as the previous inoculation with selected native mycorrhizal fungi.
Question
The Stress Gradient Hypothesis (SGH) predicts that competition and facilitation shift along stress gradients. We ask if the underlying mechanisms operate at specific points in plant life history, and if patterns are consistent along different stress gradients.
Location
Boreal, sub‐alpine and alpine grasslands in southern Norway.
Methods
We test the SGH through ontogeny along stress gradients by monitoring seedlings in intact vegetation vs bare‐ground gaps across a climatic grid of temperature and precipitation gradients. We follow one seedling cohort over two years and quantify four vital rates; emergence, survival, establishment success, and growth rate, to determine if biotic interaction effects (intact vs removed vegetation) on each of these stages shift along gradients in accordance with the SGH.
Results
We find competitive effects early in ontogeny, reflected in increased probability of seedling emergence in gaps. The magnitude of competition increases with temperature and precipitation, in line with the SGH. Growth rate of alpine seedlings was higher in intact vegetation vs gaps, indicating facilitation, and in accordance with the SGH, these effects decreased towards warmer climates. The net outcome of these processes occurring in early life history are reflected in the seedling community, where richness of emerging and surviving species is higher in bare‐ground gaps than in intact vegetation, with increasing effect toward warmer but not toward wetter sites.
Conclusion
Our results support the SGH for the earliest stages in plant life, predicting shifts from competitive to neutral or facilitative interactions toward colder climates. The biotic interaction effects on vital rates vary over ontogeny, with competition dominating for emergence whereas facilitation was more evident for seedling growth. The patterns along the precipitation gradient indicate stress at both the dry and the wet end. We highlight the importance of studies across ontogeny and along different gradients to disentangle the mechanisms underlying the SGH.
Effective grassland restoration practices can promote degraded meadows recovery. However, little has been documented regarding the effect of water addition on the restoration of degraded meadows in the Qinghai–Tibetan Plateau (QTP). A field experiment with five water addition levels was established to identify the interactions between soil bio-physicochemical properties and plant of the degraded alpine meadows in the Sanjiangyuan region, QTP. Soil enzyme activity (α-glucosidase, αG; β-1,4-glucosidase, βG; β-D-cellubiosidase, βDC; β-xylosidase, βX; β-1,4-N-acetylgucosaminidase, NAG; leucine aminopeptidase, LAP; phosphorus, P), microbial biomass C (MBC) and N (MBN), MBC: MBN, physicochemical properties (soil moisture content, SMC; bulk density, SBD; pH; total organic C, TOC; total N, TN; soil C: N; ammoniacal N, NH4⁺-N; nitrate N, NO3⁻-N; nitrite N, NO2⁻-N), and plant diversity and productivity were analyzed throughout the growing season. The results indicated that soil SMC, available N (NH4⁺-N and NO3⁻-N), TOC, the activities of αG, βDC, βX, NAG, MBC and MBN significantly increased with water addition levels, whereas the activity of LAP and P, and MBC: MBN decreased (p < 0.05). The redundancy analysis (RDA) and the subsequent path analysis found that soil biological (βG, βDC, βX, NAG, LAP, MBC, and MBN) and physicochemical properties, especially TOC, NH4⁺-N, and NO3⁻-N, were significantly related to plant diversity and productivity. The changes in soil enzyme activity (especially βDC, βG, LAP) under water addition might the key drivers affecting soil nutrients such as TOC, NO3⁻-N and NH4⁺-N, which subsequently increased plant coverage and productivity. Our findings suggested that the obviously increase in enzymes activity and nutrients might be beneficial for the vegetation recovery of degraded alpine meadow on the QTP under water addition.
The size distribution of discrete plant patches (PSD), a common descriptor of the spatial patterns of vascular vegetation, has been linked to variations in land degradation and ecosystem functioning in drylands. However, most studies on PSDs conducted to date have focused on a single or a few study sites within a particular region. Therefore, little is know on the general typology and distribution of PSDs at the global scale, and on the relative importance of biotic and abiotic factors as drivers of their variation across geographical regions and habitat types. We analyzed 115 dryland plant communities from all continents except Antarctica to investigate the general typology of PSDs, and to assess the relative importance of biotic (plant cover, frequency of facilitation, soil amelioration, height of the dominant species) and abiotic (aridity and sand content) factors as drivers of PSDs across contrasting habitat types (shrublands and grasslands). We found that both power-law and lognormal PSDs were generally distributed regardless of the region of the world considered. The percentage of facilitated species in the community drives the emergence of power-law like spatial patterns in both shrublands and grasslands, although mediated by different mechanisms (soil and climatic amelioration, respectively). Other drivers of PSDs were habitat-specific: height of the dominant species and total cover were particularly strong drivers in shrublands and grasslands, respectively. The importance of biotic attributes as drivers of PSDs declined under the most arid conditions in both habitats. We observed that PSDs deviated from power law functions not only due to the loss of large, but also of small patches. Our results expand our knowledge about patch formation in drylands and the habitat-dependency of their drivers. They also highlight different ways in which facilitation may act on ecosystem functioning through the formation of plant spatial patterns.
A single plant can interact both positively and negatively with its neighbors through the processes of facilitation and competition, respectively. Much of the variation in the balance of facilitation and competition that individuals experience can be explained by the degree of physical stress and the sizes or ages of plants during the interaction. Germination phenology partly controls both of these factors, but its role in defining the facilitation-competition balance has not been explicitly considered. I performed an experiment in a population of the winter annual Arabidopsis thaliana (Brassicaceae) to test whether germinating during physically stressful periods leads to facilitation while germinating during periods that promote growth and reproduction leads to competition. I manipulated germination and neighbor presence across two years in order to quantify the effects of the local plant community on survival, fecundity, and total fitness as a function of germination phenology. Neighbors increased survival when germination occurred under conditions that were unsuitable for survival, but they reduced fecundity in germinants that were otherwise the most fecund. Later germination was associated with facilitation in the first year but competition in the second year. These episodes of facilitation and competition opposed each other, leading to no net effect of neighbors when averaged over all cohorts. These results indicate that variation in germination timing can explain some of the variation in the facilitation-competition balance in plant communities. This article is protected by copyright. All rights reserved.
The objective of the present study was to evaluate the effects of different pre-treatments on the germination of the seeds as well as the emergence velocity of the seedlings of Erythrina velutina and Erythrina falcata. The treatments utilized for the evaluation of germination were intact seeds (control); mechanical scarification with sandpaper number 120 in the opposite side of the embryo; and immersion in water at room temperature for 6, 12, 24 and 48 hours. Four replications of 25 seeds each were used per treatment and the experimental design was completely randomized, and the comparison among the averages was made using the Tukey test at 5% of probability. The percentage of germination, the emergence velocity index and the relative frequency of germination were calculated 31 days after sowing. For both species, better percentages of germination and values of emergence velocity were obtained with the mechanical scarification of seeds. That treatment was efficient in the uniformization and anticipation of the germination process. However, the tests done with seed immersion in water at room temperature for up to 48 hours do not increase the percentage of germination of E. velutina and E. falcata seeds.
The way species affect one another in ecological communities often depends on the order of species arrival. The magnitude of such historical contingency, known as priority effects, varies across species and environments, but this variation has proven difficult to predict, presenting a major challenge in understanding species interactions and consequences for community structure and function. Here, we argue that improved predictions can be achieved by decomposing species' niches into three components: overlap, impact and requirement. Based on classic theories of community assembly, three hypotheses that emphasise related, but distinct influences of the niche components are proposed: priority effects are stronger among species with higher resource use overlap; species that impact the environment to a greater extent exert stronger priority effects; and species whose growth rate is more sensitive to changes in the environment experience stronger priority effects. Using nectar-inhabiting microorganisms as a model system, we present evidence that these hypotheses complement the conventional hypothesis that focuses on the role of environmental harshness, and show that niches can be twice as predictive when separated into components. Taken together, our hypotheses provide a basis for developing a general framework within which the magnitude of historical contingency in species interactions can be predicted.
Theoretical models predict that the net outcome of biotic interactions among plants is the sum of co-occurring negative and positive interactions, with facilitation gen- erally increasing in importance with increasing abiotic stress. However, species differ in fundamental niche optima; thus the intensity of stress is relative among species and im- portant only in the context of these relative differences. We tested the hypothesis that the facilitative response of a species is relative to how much abiotic conditions deviate from the optimum conditions for that particular species (stress), and the competitive ''response'' ability of the species (i.e., its ability to tolerate the inhibitory effects of neighbors). In a field experiment, we examined the responses of three co-occurring species with different ecological optima, Bromus erectus, Brachypodium rupestre, and Arrhenatherum elatius ,t o the alleviation of a primary limiting resource (water), and to biotic interactions in a me- soxeric grassland in eastern France. We found that A. elatius had a strong positive response to watering, the response of B. rupestre was moderately positive, and B. erectus did not respond significantly, suggesting that water stress was only important for the first two species. Most importantly, the net outcome of the interaction between each species and its neighbors depended on the degree of water stress it experienced in its natural habitat. For survival, in the control plots we found no significant interactions for B. erectus (not stressed) whereas B. rupestre and A. elatius (stressed species) were facilitated. Enhancing water availability suppressed facilitation of B. rupestre and A. elatius and led to competitive exclusion of B. erectus. In contrast to survival, there was no facilitation for growth in the control plots, and competition intensity increased for all three species with watering. In our experiment the competitive response of a species was inverse to its ability to tolerate stress, indicating a trade-off between these components of the species response. A facili- tative outcome appears to be a function of a species having both a low tolerance to a particular abiotic stress and a strong competitive-response ability.
Documents the widespread existence of ontogenetic shifts in diet and habitat and explores the consequences of such shifts for species interactions and community structure. Most examples are from the lower vertebrates and invertebrates in freshwater communities. The second part offers a conceptual framework for predicting ontogenic shifts and suggests preliminary approaches for exploring their ecological and evolutionary consequences. It is shown how such life histories may be incorporated into a population dynamics framework.-from Authors
Question: Does the proximity of shrubs affect seasonal water stress of young Austrocedrus chilensis trees (a native conifer of the Austral Temperate Forest of South America) in xeric sites?
Location: A. chilensis xeric forest in northwest Patagonia, Argentina.
Methods: We examined the dependence of predawn twig water potential on tree development (seedling to adult) and proximity to nurse shrubs during spring and summer. We analysed spatial associations of seedlings, saplings and adult trees with nurse shrubs, and also evaluated if trees affected shrub canopy vitality.
Results: Water stress in Austrocedrus trees was affected by shrub presence. Small trees (i.e.<0.5 m in height) growing in the open were most stressed, particularly in summer. Small trees growing within a shrub canopy had low water stress and little change between spring and summer. The opposite trend, however, was true for the medium-height category (i.e. 0.5-1.5 m in height); trees in this size category were more stressed when growing within the shrub canopy than in the open. Larger Austrocedrus trees (i.e.>2 m in height) were not affected by shrub presence. Austrocedrus trees were spatially associated with shrubs in all height classes; however, the percentage of living shrub canopy decreased with tree height.
Conclusions: In xeric areas of northwest Patagonia, the strength and direction of interactions between A. chilensis and shrubs, in terms of tree water stress, are dynamic and modulated by tree size and environmental conditions. Overall, positive effects of shrubs on early developmental stages appear to be more important than subsequent negative interactions, since nursing effects could generate a spatial association of shrubs and Austrocedrus trees that persists through later successional stages. These findings shed light on mechanisms behind successional changes, and have important conservation and management implications.
Aim
Theoretical models predict nurse plant facilitation enhances species richness by ameliorating stressful environmental conditions and expanding distributional ranges of stress‐intolerant species into harsh environments. We studied the role of nurse facilitation on the recruitment of perennial plants along an arid scrubland–temperate rain forest boundary to test the following predictions: (1) nurse shrub canopy increases seedling abundance and species richness along the rain forest–scrubland boundary; (2) scrubland species are less dependent on facilitative interactions than temperate rain forest species, especially at the moister, upper end of the gradient.
Location
B osque F ray J orge N ational P ark, north‐central C hile, S outh A merica (30° 39′ S – 71° 40′ W).
Methods
We examined seedling abundance and species richness of perennial plants in the open and under different types of patches that may facilitate species recruitment (living shrubs, dead shrubs, perennial grasses and trees) along an arid scrubland–temperate rain forest boundary. To assess whether the potential role of the shrub canopy on seedling survival in the scrubland and forest differs, we designed a 2 × 2 factorial field experiment with shrub canopy (under shrub or open patch) and small mammal herbivory (access or closed) as factors. At both sides of the scrubland–forest gradient, we planted young seedlings of scrubland ( S enna cumingii ) and forest ( M yrceugenia correifolia and G riselinia scandens ) species under the four treatment combinations.
Results
Nurse living shrubs increased seedling abundance and diversity. Under living shrubs, the number of recruiting species was 100% and 30% larger than in open patches of the arid scrubland and temperate rain forest patches, respectively. Seedling abundance was 60% and 300% larger under living shrubs compared to open patches of the scrubland and the temperate rain forest, respectively. Despite their low cover, dead shrubs were particularly important for recruitment of young seedlings in the scrubland. Seedlings of forest species were extremely rare. The field experiment demonstrated the importance of nurse plant facilitation for the survival of the forest species at both sides of the boundary. In contrast, scrubland species were less dependent on nurse plants than forest and intermediate forest–scrubland species.
Conclusions
Our results show that facilitative interactions increase seedling abundance and species richness along an arid scrubland–temperate rain forest boundary, notably by enhancing seedling establishment of forest species. Despite increasing nurse shrub–seedling competition in the arid scrubland, shrubs have a net positive effect on plant community diversity.
Shifts between facilitation and interference and their importance in shaping plant population and community dynamics have received wide recognition. Nevertheless, the causes and spatio-temporal scales of these shifts are poorly understood, yet strongly debated. This study tested the hypothesis that age-related changes in canopy structure shift the effect of a nurse shrub on their protégé from facilitation to interference, using as a model system the interaction between the dwarf shrub Sarcopoterium spinosum and conspecific new recruits, in the shrubland of the transition area between the Mediterranean and the semi-arid climatic zones of Israel. Foliation level (i.e. the percentage of canopy surface area covered with leaves), a measure of shrub canopy structure, increased with age. Shading level was significantly and positively related to foliation level. Densities of new recruits in the shrubland showed a unimodal response to canopy structure and cover: the highest densities were associated with canopies presenting low and medium foliation levels (providing 71 and 82% shade, respectively), while high foliation levels (93% shade) and open spaces among canopies were characterized by very low densities. A related field experiment using shading nets revealed that seedling survival rates followed a similar unimodal pattern, with the highest survival (ca 60%) detected in moderate shade (70%), twice as much as in full sun, and the lowest survival (ca 10%) observed in extreme shade (90%). These results support the study hypothesis on age-dependent interactions. Thus, in a semi-arid shrubland ecosystem, the transition of the “nurse shrub” from “young” to “old” stage can shift facilitation to interference. Hence, the age structure of established shrub populations determines a) the availability of suitable sites for seedling recruitment and b) the balance between facilitation versus interference effects on seedling establishment.
1. Ecological communities are assembled as complex networks of both positive (i.e. facilitation) and negative (i.e. competition) interactions. In networks established among plant species, many facilitative interactions occurring between a benefactor – a nurse – and a beneficiary – a facilitated seedling ‐ turn into competition over time as the facilitated seedling grows and outcompetes the nurse. The facilitative associations that disappear over time are mainly restricted to closely related taxa, because close relatives tend to share niche requirements and compete more strongly for the same resources. In consequence, the phylogenetic structure of a network might change as positive associations become negative.
2. This study is aimed to characterize how the overall (i.e. nestedness and connectance) and the phylogenetic structure of facilitation networks in semi‐arid communities change when facilitation turns into competition and some of the early species associations established by facilitation disappear.
3. We show that the initial facilitation networks retain the overall, but not the phylogenetic, structure. Phylogenetic analyses show that as seedlings, facilitated species tend to associate with the same subset of nurses while, on the contrary, nurses are indifferent to the identity of their facilitated seedlings. But when competition becomes important, closely related nurse species appear associated with only a subset of facilitated species in the community.
4. Synthesis . Temporal rearrangements in the phylogenetic structure of the facilitation networks provide evidence that plant–plant species interactions lead to highly species‐specific networks in which the phylogenetic history has a pervasive influence not only on recruitment but also on adult community composition. The use of phylogenetic methods combined with complex network approaches opens the possibility to understand the complexity of ecological interactions occurring in nature as for example those occurring when biological invasions take place or those producing coextinction cascades following species removal from ecosystems.
Most arid ecosystems have suffered from severe overexploitation by excessive wood harvesting, overgrazing, and agriculture,
resulting in depletion of vegetation biomass and soil erosion. These changes are often difficult to reverse due to positive
feedbacks that tend to stabilize the new situation. In this paper, we briefly review evidence for the idea that different
states in these ecosystems might represent alternative equilibria and present a graphic model that summarizes the implications
for their response to changing environmental conditions. We show how, in the light of this theoretical framework, climatic
oscillations such as El Niño Southern Oscillation (ENSO) could be used in combination with grazer control to restore degraded
arid ecosystems. We also present evidence that, depending on grazing pressure, ENSO episodes can trigger structural and long-lasting
changes in these ecosystems.
Current concepts of the role of interspecific interactions in communities have been shaped by a profusion of experimental studies of interspecific competition over the past few decades. Evidence for the importance of positive interactions — facilitations — in community organization and dynamics has accrued to the point where it warrants formal inclusion into community ecology theory, as it has been in evolutionary biology.
If plants cannot simultaneously acclimate to shade and drought because of physiological trade-offs, then plants are expected to be less tolerant to shading under drier conditions. One observation that, at first sight, seems incompatible with this idea is the fact that the establishment of new plants in dry areas is often restricted to shady sites under the canopy of other plants, called "nurse plants". We use a graphical model to resolve this paradox. The model visualises how facilitative patterns can be understood from the simultaneous effects of plant canopies on microsite light and moisture, and the growth responses of seedlings to those factors. The approach emphasizes the fact that positive and negative effects of plant canopies always occur simultaneously. In the presented light-water model, facilitation only occurs when the improvement in plant water relations under the canopy exceeds the costs caused by the lower light levels. This may be true under dry conditions, whereas in less dry situations, competition rather than facilitation is observed. The model shows how changes in water availability may shift interactions from competitive to faciltative and vice versa, as observed in some field patterns. It is argued that other environmental factors explaining facilitative patterns can be understood in the same context.
Harsh conditions in arid and semi-arid environments make seedling establishment rare. Plant recruitment in arid environments often occurs only in years with above average rainfall or in safe sites under the canopy of nurse plants that provide shelter from high temperatures and low moisture. Associations of establishing seedlings with adult plants are referred to as nurse-protégé interactions and are thought to be commensalisms in which seedlings benefit from the micro-environment created by adult plants with no effect for the latter. This phenomenon is thought to be more frequent in harsh than in mild environments and appears to occur frequently in deserts and arid and semi-arid biomes. Here, we investigate whether nurse-protégé interactions are more common in arid environments by searching the published literature from the previous 92 years using the terms nurse plants, protégé plants, facilitation, nucleation and facultative mutualism. We then quantitatively compared these reports from arid zones to other environments. A total of 296 papers were found which referred to nurse-protégé interactions. More than half (158) focused on arid and semi-arid zones. This information was also used to explore hypotheses of potential causative forces that might have selected for such interactions in the arid zones such as seed trapping, nutrient, moisture, protection from browsing or trampling and support availability. Because of the large number of different nurse species (147, from 98 genera and 40 families) and protégé species (429, from 273 genera and 84 families), described across a diversity of environments, we suggest that there may be more than one causative factor selecting for nurse-protégé interactions in arid and semi-arid environments.
Biotic interactions assembling plant communities can be positive (facilitation) or negative (competition) and operate simultaneously. Facilitative interactions and posterior competition are among the mechanisms triggering succession, thus representing a good scenario for ecological restoration. As distantly related species tend to have different phenotypes, and therefore different ecological requirements, they can coexist, maximizing facilitation and minimizing competition. We suggest including phylogenetic relatedness together with phenotypic information as a predictor for the net effects of the balance between facilitation and competition in nurse-based restoration experiments. We quantify, by means of a Bayesian meta-analysis of nurse-based restoration experiments performed worldwide, the importance of phylogenetic relatedness and life-form disparity in the survival, growth and density of facilitated plants. We find that the more similar the life forms of neighbouring plants are the greater the positive effect of phylogenetic distance is on survival and density. This result suggests that other characteristics beyond life form are also contained in the phylogeny, and the larger the phylogenetic distance, the less is the niche overlap, and therefore the less is the competition. As a general rule, we can maximize the success of the nurse-based practices by increasing life-form disparity and phylogenetic distances between the neighbour and the facilitated plant.
Unlabelled:
Premise of the study:
Seedling establishment and early survivorship are crucial steps for the regeneration of plant populations because both have long-lasting effects on plant population dynamics. For species recruiting through facilitation, species-specific facilitative effects might affect early fitness, an overlooked aspect in studies of facilitation considering groups of nurse species. •
Methods:
We experimentally evaluated the roles of 10 nurse species and open space on the early performance of the columnar cactus Neobuxbaumia mezcalaensis. We measured establishment, survivorship, and growth of individuals over 3 years. Moreover, to study an extended period of the ontogeny of the interaction between this cactus and its nurse plants, we also monitored survivorship and growth rates of individuals between 3 to 12 cm tall during a 3-year period. •
Key results:
Neobuxbaumia mezcalaensis performance varied significantly among nurse species, and only six yielded positive effects on early fitness. Densely canopied plants were the best nurses for this cactus. However, even among densely canopied species, some produced negative effects on the early fitness of N. mezcalaensis, indicating that similar nurse plants may elicit either facilitative or interference effects on beneficiary species. •
Conclusions:
Our results emphasize the importance of species-specific facilitative interactions in the crucial early stages in the life cycle of N. mezcalaensis and how different nurse species modify the effect of seed-rain and contribute significantly to the population dynamics of the species.
Theoretical models predict that the relative importance of facilitation and competition may vary inversely across gradients of abiotic stress. However, these predictions have not been thoroughly tested in the field, especially in semi-arid environments. In this study, we evaluated how the net effect of the tussock grass Stipa tenacissima on the shrub Pistacia lentiscus varied across a gradient of abiotic stress in semi-arid Mediterranean steppes. We fitted the relationship between accumulated rainfall and the relative neighbour index (our measures of abiotic stress and of the net effect of S. tenacissima on P. lentiscus, respectively), which varied across this gradient, to a quadratic model. Competitive interactions dominated at both extremes of the gradient. Our results do not support established theory. Instead, they suggest that a shift from facilitation to competition under high abiotic stress conditions is likely to occur when the levels of the most limiting resource are so low that the benefits provided by the facilitator cannot overcome its own resource uptake.
Plots with Two Variables Plots for Single Samples Plots with multiple variables Special Plots Summary
The effects of neighbor vegetation during succession were studied in old-field and rain forest sites of central Amazonia. We investigated how plant litter and the availability of soil nutrients (P and K) influenced interactions between neighbor vegetation and colonizing species. We monitored the establishment and growth of seedlings of four tree species, sown in old-field and forest plots in which vegetation, plant litter, and soil P and K were experimentally manipulated. In the old field, removal of vegetation significantly decreased seedling establishment of Oenocarpus bataua, Socrathea exorrhiza, and Aspidosperma discolor (suggesting facilitation in these late successional species) but had no effect on Inga edulis (a mid successional species). In contrast, neighboring vegetation inhibited the growth of all sown species: removal significantly increased biomass. In the forest site, removal of forest vegetation had no effect on establishment but significantly increased seedling mass, suggesting inhibition. Plant litter removal significantly decreased seedling establishment of all species in the old field, and of S. exorrhiza and I. edulis in the forest, suggesting positive effects. A significant interaction between plant litter and vegetation removal for O. bataua and S. exorrhiza in the old field showed that litter may also contribute to facilitation. Seedling mass of the three late-successional species was consistently not enhanced by P and K addition. In I. edulis, however, mass increased 2.5 times after P and K addition when vegetation was removed but did not vary in intact old-field vegetation. Seedling establishment in the old field was significantly higher in S. exorrhiza and A. discolor compared to the forest, while plant biomass in S. exorrhiza, A. discolor, and I. edulis was significantly higher. Neither plant litter nor P and K addition could account for these differences. We conclude that facilitation and competition may operate during the early stages of forest succession in Amazonia, that plant litter contributes to the facilitation process, and that soil P and K do not influence the inhibition process, suggesting that light competition may be important. As succession proceeds, the effects of neighbor vegetation switch from positive to negative.
Seedlings of the cactus Carnegiea gigantea at 2 sites in the Sonoran Desert were found only in sheltered microhabitats, 89% occurring under the canopy of Ambrosia deltoidea and Cercidium microphyllum. In contrast, 29% of the seedlings of Ferocactus acanthodes, which tolerates higher temperatures than C. gigantea, occurred in unsheltered microhabitats, where maximum soil surface temperatures reached 71°C. Most (70%) of the sheltered seedlings of F. acanthodes occurred under the canopy of the perennial bunchgrass Hilaria rigida. Nurse plants facilitate seedling establishment by reducing high temperatures near the soil surface and provide a microhabitat with a higher soil N level, but shading and competition for water with the nurse plants markedly reduce seedling growth. -from Authors
Retama sphaerocarpa is a leafless leguminous shrub found in most regions of Spain, frequently with a growth of herbs in its understorey which contrasts with the surrounding areas by its higher biomass and diversity. We examined the relationships between the shrub and the herbs underneath along a gradient of shrub age. A total of fifty individuals were selected to fit five age classes and shrub characteristics, soil properties and flora under the canopy were examined along the estimated chronosequence. All shrub size variables increased with time, as did the amount of nutrients stored by the shrub, but differences were often significant only between the three oldest classes. Concentration of nitrogen and phosphorus in photosynthetic stems remained constant, but nutrient pools in stem biomass increased with time. The shrubs changed the soil environment under their canopies with age by ameliorating soil texture, nutrient content and capacitance of water. The improvement was most pronounced between the two oldest classes (IV and V), and was probably due to the high biomass of perennial species in the understorey which increased the production of litter, and the interception of wind-blown dust. Plant diversity in the understorey increased with shrub age, likely due to a greater heterogeneity under larger canopies. Drought-resistant species, typical of the open areas between shrubs, were displaced from the centre of the understorey by taller, more mesic species over the age gradient. Retama sphaerocarpa shrubs benefited from the increase of resources in the understorey and showed a higher reproductive output with shrub age, but decreased at the beginning of senescence. The indirect interactions between R. sphaerocarpa and its understorey herbs could be considered as a two-way facilitation in which both partners benefit from their association.
Direct positive interactions (mutualisms and commensalisms) are generally accepted as important processes in communities. They appear to be most common in environments with relatively high physical disturbance, stress, or predation, where associated species can increase the growth and survival of other species unable to survive in isolation. Although ecologists have documented direct positive interactions among species for decades, there is less known about how these interactions affect community species diversity patterns. In this paper, we present a qualitative theoretical model that considers how direct positive interactions affect community species diversity. The model uses, as its basis, familiar unimodel species diversity models (i.e., "compensatory mortality" and "intermediate disturbance" hypothesis) to understand where direct positive interactions are likely to be important. Initially, it predicts that direct positive interactions increase species diversity by facilitating species that might not normally survive under very high physical disturbance, stress, or predation. In addition, it suggests that, under intermediate physical disturbance, stress, or predation, facilitator species that might normally be competitively excluded are released from competition. We suggest that facilitator species may then create new interaction webs that would not be possible in their absence. To illustrate these ideas, we describe a case study taken from a New England salt marsh community where a gradient in physical conditions occurs. In this community, direct positive interactions, and their indirect effects, are predicted to increase the species diversity by at least 35%. This empirical case study and model show that by incorporating direct positive interactions into ecological experiments and theory, it is possible to expand our understanding of the mechanisms responsible for community species diversity patterns.
Interactions among species determine local-scale diversity, but local interactions are thought to have minor effects at larger scales. However, quantitative comparisons of the importance of biotic interactions relative to other drivers are rarely made at larger scales. Using a data set spanning 78 sites and five continents, we assessed the relative importance of biotic interactions and climate in determining plant diversity in alpine ecosystems dominated by nurse-plant cushion species. Climate variables related with water balance showed the highest correlation with richness at the global scale. Strikingly, although the effect of cushion species on diversity was lower than that of climate, its contribution was still substantial. In particular, cushion species enhanced species richness more in systems with inherently impoverished local diversity. Nurse species appear to act as a 'safety net' sustaining diversity under harsh conditions, demonstrating that climate and species interactions should be integrated when predicting future biodiversity effects of climate change.
After a millenarian history of overexploitation, most forests in the Medi- terranean Basin have disappeared, leaving many degraded landscapes that have been re- colonized by early successional shrub-dominated communities. Common reforestation tech- niques treat these shrubs as competitors against newly planted tree seedlings; thus shrubs are cleared before tree plantation. However, empirical studies and theory governing plant- plant interactions suggest that, in stress-prone Mediterranean environments, shrubs can have a net positive effect on recruitment of other species. Between 1997 and 2001, we carried out experimental reforestations in the Sierra Nevada Protected Area (southeast Spain) with the aim of comparing the survival and growth of seedlings planted in open areas (the current reforestation technique) with seedlings planted under the canopy of preexisting shrub species. Over 18 000 seedlings of 11 woody species were planted under 16 different nurse shrubs throughout a broad geographical area. We sought to explore variation in the sign and magnitude of interactions along spatial gradients defined by altitude and aspect. In the present work, we report the results of a meta-analysis conducted with seedling survival and growth data for the first summer following planting, the most critical period for reforestation success in Mediterranean areas. The facilitative effect was consistent in all environmental situations explored (grand mean effect size d 1 5 0.89 for survival and 0.27 for growth). However, there were differences in the magnitude of the interaction, depending on the seedling species planted as well as the nurse shrub species involved. Additionally, nurse shrubs had a stronger facilitative effect on seedling survival and growth at low altitudes and sunny, drier slopes than at high altitudes or shady, wetter slopes. Facilitation in the dry years proved higher than in the one wet year. Our results show that pioneer shrubs facilitate the establishment of woody, late-successional Mediterranean spe- cies and thus can positively affect reforestation success in many different ecological settings.
Traditional ecological models have focused mainly on competition between plants, but recent research has shown that some plants benefit from closely associated neighbors, a phenomenon known as facilitation. There is increasing experimental evidence suggesting that facilitation has a place in mainstream ecological theory, but it also has a practical side when applied to the restoration of degraded environments, particularly drylands, alpine, or other limiting habitats. Where restoration fails because of harsh environmental conditions or intense herbivory, species that minimize these effects could be used to improve performance in nearby target species. Although there are few examples of the application of this "nursing" procedure worldwide, experimental data are promising, and show enhanced plant survival and growth in areas close to nurse plants. We discuss the potential for including nurse plants in restoration management procedures to improve the success rate of such projects.
We propose an index to measure the relative interaction intensity in plants (RII) with strong mathematical and statistical properties which overcome problems shown by other frequently used indices. RII has defined limits [-1, +1]; is symmetrical around zero, with identical absolute values for competition and facilitation; is linear; and does not have discontinuities in its range. It is therefore safe to use in statistical and mathematical operations. RII distribution is approximately normal, with means equal to the true population index and a sampling variance that can be derived. Its strong statistical properties make RII proper for use in parametric meta-analyses. It can be applied to any kind of interaction (from competitive exclusion to symbiosis) and in commonly published ranges of interaction intensity it offers the most consistent results. Because RII uses basic arithmetical operators, it can be scaled up and used to measure multispecific interactions at the community level.
1. The relative contribution of positive and negative interactions to the organization of ecological communities is an important area, though poorly understood because of the complexity inherent to long-term interactions. For example, positive interactions like plant facilitation turn into negative interactions (competition) along the ontogeny of a plant or in response to temporal fluctuations in the environment. Furthermore, when many plants grow together indirect effects are usually positive and alleviate direct competitive effects.
2. The large number of direct and indirect interactions potentially occurring in natural communities and the temporal scale necessary to account for the ontogenetic shifts in the sign of the interaction makes a fully experimental approach prohibitive. Here, we propose that the phylogenetic distance among co-occurring species is a good proxy to detect competition as a long-term force assembling community composition. Our proposal is based on the observation that closely related species tend to be phenotypically similar and therefore compete for the same niche.
3. We test the relationship between phylogenetic relatedness and the persistence of pairwise (nurse-facilitated) interactions occurring between 102 woody species in three Mexican semi-arid communities in order to quantify the balance between competition and facilitation at the community level.
4. Our results indicate that facilitation turns into competition with increasing taxa relatedness. After validating the association between competition and phylogenetic relatedness, we estimate that 57% of the interactions remain with time while 43% become competitive. [Correction added after publication, 4 March 2008: in the preceding sentence, values corrected from 53% and 47%, respectively.] The preponderance of positive interactions may be explained if facilitation is considered as a mutualism in which both species benefit leading to vegetation clumps in communities.
5. Synthesis . We provide a new perspective on the balance between positive and negative interactions based on a phylogenetically structured network of interactions. This approach promises to contribute to our understanding of long standing issues in plant ecology and to reveal new areas of future research by testing the existence and the nature of the mutualisms as well as their complexity–stability properties on communities as a whole.
Facilitation of tree establishment by nurse shrubs, which ameliorate otherwise unfavourable microenvironmental conditions, is a widely studied phenomenon. However, relatively little is known about how facilitative influences change in relation to interannual climatic variability. In northern Patagonia, Argentina, we examined influences of potential nurse shrubs on the establishment of those influences to establishment during yeras of contrasting climate. We also investigated the effects of nurse shrubs and different water availability on tree seedling emergence and survival.
A strong spatial association of Austrocedrus juveniles with shrubs, both beneath shrub canopies and near shrub canopies, indicates that shrubs favourably influence tree regeneration and that in some habitats and time periods nurse plants appear to be required for successful tree seedling establishment. Protection from direct sunlight was the main factor contributed by shrubs that enhanced the germination and survival of Austrocedrus. During the 1995-1996 experiment, no seedlings were survived in the unwatered interspaces between shrubs, whereas maximal survival was obtained by watering seedlings at shaded sites.
The results of this study indicate that in the Patagonian ecotone the strength of facilitative associations between shrubs and Austrocedrus juveniles closely tracks climatic variability. During extremely warm dry years, recruitment of Austrocedrus is nil with or without protection by nurse shrubs. During cool wet years, establishment may occur both beneath shrubs and in open interspaces; however, during average years, which are still years with substantial drought stress, establishment of Austrocedrus appear to require nurse shrubs.
Abstract Three experiments were conducted to verify if an increase in environmental stress level would affect the interactions between two species of nurse shrubs and seedlings of Aspidosperma quebracho-blanco. This is a mesic species with a generalist distribution over an extensive environments gradient. The relationship between Larrea divaricata and seedlings of A. quebracho-blanco was studied in two contrasting soils, a silty loam soil with higher surface clay content and a sandy loam soil. The effect of seasonal variability of rainfall on the initial establishment of seedlings under the shade of L. divaricata was evaluated in three consecutive years. The effect of nurse plant shade was tested comparing two shrub species with different types of leaf life span (sclerophyllous-evergreen and leguminous-deciduous). The natural establishment of A. quebracho-blanco depended on shaded microsites, but not on the type of shade provided by different nurse shrubs. Emergence and initial establishment depended on interactions of soil type and seasonal rainfall variation with nurse plants. The importance of facilitation increased with clay soil (CS). Sandy soil was ‘less humid’ than CS under shrub shade. However, establishment success depends on opportune even rainfall distribution in interaction with nurse plant presence.
1 Interactions among plants strongly influence the structure and dynamics of plant populations and communities. However, most empirical studies of plant–plant interactions failed to make repeated measures of responses to neighbouring individuals and thereby neglected possible changes in interactions throughout the life history of the plants. 2 We tested the hypothesis that competition between annual species intensifies from early to late life-history stages, by sequentially measuring interactions in neighbour-removal experiments at three study sites located along a rainfall gradient in Israel. 3 Two annual species, Biscutella didyma and Hymenocarpos circinnatus , grew with and without neighbours in their natural habitats. Five response variables representing consecutive life-history stages (seedling survival, juvenile biomass, adult survival, number of seeds and final biomass) were recorded throughout the whole growing season. 4 The direction and intensity of interactions varied considerably between environments and life stages. On average, growth-related response variables indicated higher compe-tition intensity at the productive end of the climatic gradient, while survival indicated either facilitation at the dry end or no trend along the gradient. 5 Temporal changes occurred, with moderate facilitation soon after germination shifting to strong competition at the end of the growing season. 6 Our results demonstrate that the outcome of experimental studies on plant–plant interactions may depend not only on the environmental productivity but more so on the life stage at which the target plant is studied.
The stress‐gradient hypothesis (SGH) predicts that the frequency of facilitative and competitive interactions will vary inversely across abiotic stress gradients, with facilitation being more common in conditions of high abiotic stress relative to more benign abiotic conditions. With notable exceptions, most tests of the SGH have studied the interaction between a single pair or a few pairs of species, and thus have evaluated shifts in the magnitude and direction of pair‐wise interactions along stress gradients, rather than shifts in the general frequency of interactions.
The SGH has been supported by numerous studies in many ecosystems, has provided a crucial foundation for studying the interplay between facilitation and competition in plant communities, and has a high heuristic value. However, recent empirical research indicates that factors like the variation among species and the nature of the stress gradient studied add complexity not considered in the SGH, creating an opportunity to extend the SGH's general conceptual framework.
We suggest that one approach for extending the SGH framework is to differentiate between the original idea of how ‘common’ interactions might be along stress gradients and the ubiquitous empirical approach of studying shifts in the strength of pair‐wise interactions. Furthermore, by explicitly considering the life history of the interacting species (relative tolerance to stress vs. competitive ability) and the characteristics of the stress factor (resource vs. non‐resource) we may be able to greatly refine specific predictions relevant to the SGH.
We propose that the general pattern predicted by the SGH would hold more frequently for some combinations of life histories and stress factor, particularly when the benefactor and beneficiary species are mostly competitive and stress‐tolerant, respectively. However, we also predict that other combinations are likely to yield different results. For example, the effect of neighbours can be negative at both ends of the stress gradient when both interacting species have similar ‘competitive’ or ‘stress‐tolerant’ life histories and the abiotic stress gradient is driven by a resource (e.g. water).
Synthesis. The extension of the SGH presented here provides specific and testable hypotheses to foster research and helps to reconcile potential discrepancies among previous studies. It represents an important step in incorporating the complexity and species‐specificity of potential outcomes into models and theories addressing how plant–plant interactions change along stress gradients.
1. Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field. 2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant-plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research. 3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies. 4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity. 5. Certain ecological modelling approaches (e.g. individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes. 6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms. 7. Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers. 8. Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant-plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology. 9. Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists.
Successional pathways were evaluated in two Amazonian secondary forest communities with different land‐use histories. Sites which had been clearcut without subsequent use were dominated after 6–10 years by the pioneer genus Cecropia (Moraceae), whereas those used for pasture before abandonment were dominated by the pioneer genus Vismia (Clusiaceae).
There were 58 plant families and 300 species identified in Cecropia stands but only 43 families and 147 species were identified in Vismia stands. There were 77 species in common (Sorensen similarity = 0.34).
Differences in species number and composition of recruiting individuals between stand types were significant and were a function of the dominant pioneer genus, stem density, distance from primary forest, and land‐use history. Regeneration under Vismia canopy was dominated by small Vismia individuals (25% of plants < 2 cm basal diameter), whereas regeneration under Cecropia canopy was more diverse and did not include a single young Cecropia .
The number of regenerating plants in both secondary stand types dropped off sharply with distance (5, 25, 50, and 100 m) from primary forest, suggesting that seed dispersal was limiting plant recruitment. Species richness also declined with distance and could be explained by the decline in plant density. Species richness in Cecropia stands increased linearly with plant density, but in Vismia stands the richness increase with density was a decelerating function.
For the central Amazon, secondary succession involves a more rapid return of primary forest species if deforestation is not followed by use as pasture before abandonment.
1. Although the consequences of facilitation at individual and population levels are well known, the community-level consequences of these processes have received much less attention. In particular, the importance of facilitation in determining richness at the entire community level has seldom been evaluated.
2. In this study, we sampled 11 alpine plant communities along the southern Andes in South America, spanning from tropical (25°S) to sub-antarctic latitudes (55°S). Plant communities were dominated by cushion plants, a particular growth form that acts as a nurse plant for other plant species. Through rarefaction curves, we assessed the effectiveness of community sampling and estimated the number of species present within and outside cushions. Non-metric Multidimensional Scaling ordinations (NMDS) were used to assess differences between the species assemblages growing within and outside cushions. Finally, samples from cushions and open areas were combined in a single matrix accounting for the difference in cover between both microhabitats, and through rarefaction curves we assessed how many more species are added to the community due to the presence of cushions.
3. Samples taken within cushions always contained more species than equivalent samples from open areas. However, the magnitude of this difference varied among communities. NMDS ordination indicated that cushions generate species assemblages structurally different from those found in open areas. Inclusion of samples from cushion and open areas in synthetic analyses – where differences in cover were accounted for – indicated that the presence of cushions consistently increased species richness at the entire community level. The magnitude of these increases in species richness varied with habitat severity, with lower values at both extremes of the environmental severity gradient.
4.Synthesis. Facilitative interactions with cushion nurse plants along the high Andes of southern South America changed plant assemblage structure and increased species richness at the entire community level, indicating that facilitative interactions are pivotal in maintaining the diversity of these harsh environments.
1. Traditionally, techniques of plant manipulation during restoration have focused on the reduction of competition by ‘problematic’ existing vegetation. However, the increasing recognition of facilitation as a main process regulating the composition of communities has brought a change in the practice of restoration towards a better awareness of the benefits inherent to conserving neighbouring vegetation.
2. Here, I provide the results of a meta-analysis of published studies that have manipulated interactions among plants with the objective of restoring degraded terrestrial systems. I created four different data sets corresponding to the variables most commonly used to measure plant performance (i.e. emergence, survival, growth and density), and asked whether the benefits of facilitation as a restoration tool vary depending on the study duration, the life-form of the neighbour and target species, and the ecosystem type.
3. Neighbour effects varied strongly among performance estimators. Positive effects were frequently found for emergence and survival, whereas neutral or negative interactions predominated for growth and density.
4. No clear support existed for a relationship between study duration and neighbour effect.
5. The life-form of the interacting species, particularly of neighbours, largely influenced the interaction outcome. Herbs had strong negative effects, especially on other herb species, whereas shrubs had large facilitative effects, especially on trees.
6. Semiarid and tropical systems showed in general more positive neighbour effects than wetlands and particularly mesic temperate systems, where negative interactions predominated. However, these results were largely influenced by the over-representation of herb species in wetlands and temperate habitats, survival facilitation being found in all systems when only woody species were considered.
7. Synthesis. Pre-existing vegetation can have large impacts on species establishment in degraded habitats. Inhibition predominates in herbaceous communities typical of early-successional stages, whereas facilitation prevailes in communities dominated by shrubs and trees. Even productive systems (e.g. mesic temperate habitats) appear suitable for the application of facilitation as a restoration tool of woody communities. Whereas restoring herbaceous communities seems largely reliable on removal techniques, augmenting populations of nurse shrubs and trees should be considered a promising strategy for restoring woody late-successional communities.
Summary • Where competition with established vegetation limits plant recruitment, fires create open conditions which can allow invasive species to establish. However, facilitation theory suggests that destruction of vegetation will restrict germination and survival. These hypotheses were tested in a long-term study of establishment by Pinus sylvestris– a globally important invasive – on English temperate heaths. • Pine seeds were sown at 10 sites which represented replicated stages of heath recovery after fire: from bare soil to dense, tall vegetation. • Seedling emergence varied among stages from 3% to 36% and was closely related to vegetation density, increasing with lower shrub height. The same pattern was evident within sites where seedlings emerged mostly at sowing locations with little or no vegetation. • Yearly seedling survival showed a quadratic relationship with vegetation density over the first 4 years; with extremely high (> 95%) mortality in both very open and very dense conditions, but low mortality (• The initial conditions after fire constrain invasion because high emergence is countered by high mortality. However, the moderate shrub density during the first decade post-fire enhances P. sylvestris seedling survival and so promotes invasion. Invasibility is low in dense mature heath, but becomes high as shrubs collapse in degenerate heath which increases seedling emergence and survival. • Synthesis. This study provides evidence that facilitation can occur in temperate regions, and that the plant interactions within a heathland community are a balance of competition and facilitation. This balance is governed by vegetation structure and plant ontogeny. Dominance of competition in more dense vegetation and for seedling emergence changed to facilitative effects in less dense vegetation and for older seedlings.
Question: How does the interaction between two dominant shrub species in a coastal sand dune community change during their life history? Does this interaction influence their population dynamics?
Location: A semiarid coastal sand dune system in southeast Spain.
Methods: For 3 years we monitored physiological status, growth and reproductive effort of Juniperus phoenicea and Pistacia lentiscus , the dominant shrub species, growing either alone or in close spatial association. We also recorded adult mortality patterns and characterized seedling survival, soil properties and microclimate conditions beneath canopies and in bare ground.
Results and conclusions: There was a strong bi‐directional interaction between the two studied species, with a net balance that changed in sign with increasing plant development. While mature individuals facilitated the establishment of seedlings of both species, adult mortality patterns suggested asymmetric competition at later life stages. The interaction with Pistacia negatively affected growth of juniper and contributed to its high mortality rates, while juniper had almost no effect on mature Pistacia individuals. Physiological data suggested that Pistacia had a competitive advantage over juniper, most likely because of differences in rooting patterns and tolerance to salinity, which may determine the source of water available for each species. Community dynamics are governed by facilitation at the seedling stage and shaped by differences in physiological traits in adult plants. Plant‐plant interactions, which are strongly affected by environmental gradients, are important drivers of community dynamics in this system.
The effects of neighboring vegetation and soil fertility on the establishment, survival and growth of tree species were studied in a subtropical old-field area in south Brazil. Seed damage, germination and seedling establishment of four tree species plus growth and survival of two transplanted tree species were monitored under factorial combinations of the following treatments: (1) pioneer vegetation (presence and absence); (2) soil fertility (addition of NPK and control). Facilitation was the main process affecting plant performance. The presence of pioneer vegetation significantly improved germination, establishment, growth and survival of most study species. Around 90% of sown seeds were damaged and the removal of pioneer vegetation significantly increased seed damage for all species studied, decreased germination in three out of four species, and decreased establishment in one species. Moreover a significantly higher seedling growth rate of Ingavirescens was found after the first year of the experiment in plots where vegetation was present. The presence of vegetation significantly increased seedling survival of I.virescens by protecting seedlings from leaf loss due to winter frosts. Competition was detected by the second year when a higher growth of transplanted seedlings of the species Araucariaangustifolia occurred in plots where vegetation was present and fertilizer were applied. A lower growth rate was detected in plots where vegetation was present but fertilizer was not applied. These results indicate a balance between competition for soil nutrients and protection by neighbor vegetation. Damage of seedlings by leaf cutter ants was an important barrier for plant survival. Damage occurred in 80% of the A.angustifolia seedlings and 58% of these damaged seedlings died. The presence of neighboring vegetation tended to protect seedlings from ant damage. Although competition occurred, facilitation seems to be the main process driving early successional changes in this subtropical old field. This was mainly due to the improvement of local microclimatic conditions and protection against herbivores by neighboring vegetation. Facilitation occurred during establishment and growth phases in a subtropical area that is considered a productive, low stress environment. Our results indicate that facilitation may be more frequent in productive environments than previously thought.
1) The downy oak (Quercus humilis) has recently colonised the Causse du Larzac plateau in southern France. We studied the influence of the shrubs Buxus sempervirens and Juniperus communis on Q.humilis establishment and of Buxus on the growth of established Q.humilis individuals
2) Percentage germination of experimetnally planted Q.humilis was higher under shrubs than in nearly open areas and higher on the north than south side of the canopy. Germination where part of the canopy has been removed was similar to that away from the shrubs, suggesting that the facilitation mechanism is related to changes in microclimate rather than to a soil effect.
3) When exposed to sheep for 1 month, 100% of 326 unprotected oak seedlings were grazed, causing a 44% mortality. The presence of Buxus and Juniperus improved seedling survival by protecting them against sheep grazing and summer drought. Predation by rodents was, however, greater under shrub cover.
4) The highest leaf dry mass of oak seedlings was recorded under Juniperus where light conditions seem more favourable for growth than under Buxus (direct effect) or in grassland (indirect effect). The growth of naturally established individuals of Q.humilis (in terms of total leaf mass per annual branch and width of rings) was lower than under Buxus than in grassland but the values became similar once the canopy was overtopped.
5) The balance between positive and negative interactions varied in relation to the life stage of Q.humilis and the two shrub species. Regenration of Q.humilis in open grassland was prevented by grazing. The protection offered by shrubs continues of offset the negative interference on growth, particularly under Buxus, so that plants could survive to overtop the shrub canopy and reach maturity. The succession pathway therefore depends closely on the distribution of shrubs in the grassland.
1 Spatiotemporal responses to habitat conditions are important components of plant population and community dynamics. Plant stage or size is a common predictor of plant performance for a range of ecological conditions, including responses to neighbours. Plant response to local conditions varies from seedling establishment through to senescence, with strong implications for population regulation.
2 I investigated size-dependent responses to near adult neighbours among a uniquely quantitative sample of mapped juvenile and adult bur-sage (Ambrosia dumosa), a common shrub in the Colorado Desert of California.
3 Analyses of juvenile establishment and survival for two 5-year census periods from 1984 to 1989 and 1989 to 1994 determined that germination and survival was greater for juveniles located under adults compared with away from adults. However, analyses of neighbour effects on growth of plants from the 1984 cohort showed that near adult neighbours improved juvenile growth over the 10-year interval from 1984 to 1994, but reduced adult growth.
4 A size-dependent, ontogenetic shift occurs because neighbouring adult plants significantly improve the demographic performance of juveniles, but diminish that of larger established plants.
5 The ontogenetic niche shift may be a useful framework to describe such differential responses of juvenile and adult plants. The utility of this framework is that responses to spatial and temporal variability in the environment are clearly demonstrated through ontogenetic constraints on plant performance, which provide an alternative mechanism of coexistence within and between species.
Indirect facilitation occurs when the indirect positive effects of one species on another, via the suppression of a shared competitor, is stronger than the direct competitive effect. Although theory predicts that these interactions may be more common in assemblages of 3 or more competitors, experimental studies of this process are rare. Here, I report a study of a northern Californian riparian community, where I tested the hypothesis that the sedge Carex nudata had direct competitive effects on other plants species, as well as indirect facilitative effects, by suppressing a second competitor, the common Monkey Flower Mimulus guttatus. Results of a field experiment, in which I manipulated the presence of Carex and M.guttatus in a factorial design, uncovered 3 qualitatively different interactions between Carex and 3 target species. I found evidence of indirect facilitation for the liverwort Conocephalum conicum, such that Carex "facilitated" Conocephalum in the absence of M.guttatus. Plant distribution patterns supported the widespread occurrence of this interaction. Carex also had an indirect positive effect on the scarlet monkey flower M.cardinalis, though the magnitude of this effect was similar to direct Carex competition. Lastly, Carex plant interactions in this study are discussed and incorporated into a general hypothesis that indirect facilitation among competitors is most important in assemblages of species that vary in competitive mechanism.
The effects of neighbouring vegetation during succession were studied in oldfield and rainforest sites of central Amazonia. We investigated how plant litter and the availability of soil nutrients(P & K) influenced interactions between neighbouring vegetation and colonising species. We monitored the establishment and growth of seedlings of four tree species, sown in old-field & forest plots in which vegetation, plant litter, and soil P & K were experimentally manipulated. In the old field, removal of vegetation significantly decreased seedling establishment of Oenocarpus batana, Socrathea exorrhiza, and Aspidosperma discolor(suggesting facilitation iin these late-successional species) but had no effect on Inga edulis(a mid-successional species). In contrast, neighbouring vegetation inhibited the growth of all sown species; removal significantly increased biomass. In the forest site, removal of forest vegetation had no effect on establishment but significantly increased seedling biomass, suggesting inhibition. Plant litter removal significantly decreased seedling establishment of all species in the old field, and of S.exorrhiza and I.edulis in the forest, suggesting positive effects. A significant interaction between plant litter and vegetation removal for O.batana and S.exorrhiza in the old fieldin the old field showed that litter may also contribute to facilitation. Seedling mass of the three late-successional was consistently not enhanced by P & K addition. In I.edulis, however, mass increased 2.5 times after P & K when vegetation was removed but did not vary in intact oldfield vegetation. Seedling establishment in the oldlfield was significantl;y higher in S.exorrhiza and A.discolor compared to the forest, while plant biomassin S.exorrhiza, A.discolor, and I.edulis was significantly higher. Neither plant litter nor P and K addition could account for these differences. We conclude that facilitation and competition may operate duringt eh early stages of forest succession in Amazonia, that plant litter contributes to teh facilitation process, and that soil P & K do not influence the inhibition process, suggesting that light competition may beimportant. As succession proceeds, the effects of neighbouring vegetation switch from positive to negative.
Positive interactions among plants, or facilitations, have been demostrated in a wide variety of communities around the world(see reviews by DeAngelis et.al.1986; Hunter & Aarssen 1988; Bertness & Callaway 1994; Callaway 1995, Callaway & Walker in press). Neighbouring plant species compete with one another for resources, but they may also provide benefits for each other such as shade, higher nutrient levels, soil oxygenation, protection from herbivores, more favourable soil microflora, transfer of resources and fixed carbon via mycorrhizae, and increased pollinator visits(Callaway 1995).
The species-specificity of positive interactions among plants - whether or not benefactor species are highly interchangeable - is central to understanding the general role of positive interactions in plant communities. In other words, are the positive effects of plants simply due to general changes in the biophysical environment; that which can be imitated by inanimate objects like rocks, microtopography, or experimental shade cloth? Or can facilitation depend on the species, with some species eliciting strong positive effects and other morphologically similar species producing neutral or negative effects? The species-specificity of positive interactions is pertinent to our general concepts of plant communities(see Gleason 1926; Goodall 1963; Shipley & Keddy 1987; Austin 1990; Collins et.al.1993; Callaway 1997). If positive interactions are often speciec specific, then many plant communities may be more independent than currently thought.
Here, I have explained the specificity of positive interactions among plants by examining the literature and asking the following questions
1) Are beneficiary species non-randomly associated with potential benefactors?
2) Are positive mechanisms produced by species specific plant traits?
3) Can potential benefactors have similar positive effects, but different negative ones?
Interactions among organisms take place within a complex milieu of abiotic and biotic processes, but we generally study them as solitary phenomena. Complex combinations of negative and positive interactions have been identified in a number of plant communities. The importance of these two processes in structuring plant communities can best be understood by comparing them along gradients of abiotic stress, consumer pressure, and among different life stages, sizes, and densities of the interacting species. Here, we discuss the roles of life stage, physiology, indirect interactions, and the physical environment on the balance of competition and facilitation.
1. Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field.
2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant–plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research.
3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations
of previous studies.
4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity.
5. Certain ecological modelling approaches (e.g. individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes.
6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms.
With the advent of molecular phylogenies the assessment of community assembly processes has become a central topic in community ecology. These processes have focused almost exclusively on habitat filtering and competitive exclusion. Recent evidence, however, indicates that facilitation has been important in preserving biodiversity over evolutionary time, with recent lineages conserving the regeneration niches of older, distant lineages. Here we test whether, if facilitation among distant-related species has preserved the regeneration niche of plant lineages, this has increased the phylogenetic diversity of communities. By analyzing a large worldwide database of species, we showed that the regeneration niches were strongly conserved across evolutionary history. Likewise, a phylogenetic supertree of all species of three communities driven by facilitation showed that nurse species facilitated distantly related species and increased phylogenetic diversity.