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Fire responses of flora in a sclerophyll–rainforest vegetation complex in the Nightcap Range, North Coast, New South Wales
Abstract
Context Species fire responses were investigated in a mixed sclerophyll–rainforest ecosystem in the Nightcap Range, North Coast, New South Wales. Aims To examine rates of seedling recruitment and resprouting in functional and phytogeographic components of wet sclerophyll forest (WSRf), and adjacent open forest (OF) and rock outcrop shrubland (RO). Methods Species resprouting and seedling recruitment traits (fire responses) were recorded in 45 stem plots and 225 seedling subplots in WSRf, OF and RO. Species fire responses were classified, community fire-response spectra compiled and rates of seedling recruitment and resprouting in WSRf examined in relation to primary fire response, growth-form, habitat and broad functional and phytogeographic species groupings. Species size-regenerative class distribution was used to analyse population structure, fire impact, regeneration and recruitment in resprouter species that comprised most of the mesic-Gondwanan element of the WSRf flora. Key results WSRf, OF and RO habitats had distinctively different fire-response spectra. In WSRf, there was a high proportion of mesophyll resprouter species of Gondwanan origin with nil or very low seedling recruitment, a distinct component of mesophyll seeders of Indo-Malayan origin, as well as sclerophyll seeders and resprouters that also comprised most of the OF and RO floras. Resprouters comprised 75% of the WSRf flora, 50% OF and 10% pavement shrubland. Continuous size-class distributions indicated recruitment between fire events in the majority of mesophyll resprouters in WSRf. Lower total seedling density appeared to reflect inherent species traits and less canopy disturbance by fire. Large sclerophyll species forming the unburnt canopy of WSRf had very low seedling recruitment. Conclusions Different habitats (WSRf, OF and RO) and functional and phytogeographic clades in WSRf display distinctive patterns of resprouting and seedling-recruitment fire response. Fire responses of species that maintain species population and community composition are governed by fire regime, habitat variables and inherent species traits. Implications The distinctive fire-response spectrum of WSRf appears to be a direct consequence of the overlap of ‘new’ and ‘old’ floras in this broad vegetation type.
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In 2019, south-eastern Australia experienced its driest and hottest year on record, resulting in massive canopy dieback events in eucalypt dominated forests. A subsequent period of high precipitation in 2020 provided a rare opportunity to quantify the impacts of extreme drought and consequent recovery. We quantified canopy health and hydraulic impairment (native percent loss of hydraulic conductivity, PLC) of 18 native tree species growing at 15 sites that were heavily impacted by the drought both during and 8–10 months after the drought. Most species exhibited high PLC during drought (PLC:65.1 ± 3.3%), with no clear patterns across sites or species. Heavily impaired trees (PLC > 70%) showed extensive canopy browning. In the post-drought period, most surviving trees exhibited hydraulic recovery (PLC:26.1 ± 5.1%), although PLC remained high in some trees (50–70%). Regained hydraulic function (PLC < 50%) corresponded to decreased canopy browning indicating improved tree health. Similar drought (37.1 ± 4.2%) and post-drought (35.1 ± 4.4%) percentages of basal area with dead canopy suggested that trees with severely compromised canopies immediately after drought were not able to recover. This dataset provides insights into the impacts of severe natural drought on the health of mature trees, where hydraulic failure is a major contributor in canopy dieback and tree mortality during extreme drought events.
ContextTreeless areas in forested landscapes are an enduring ecological puzzle globally. A fire-mediated alternative stable state (FMASS) model has been proposed to explain mosaics of forest and sedgeland in Tasmania, whereby shifts in fire frequency change vegetation and soil patterns. This model is controversial, and a key step in proving it demands elucidating post-fire vegetation dynamics at landscape-scales and over historical timeframes.Objectives
To quantify historical changes in extent of a large sedgeland patch surrounded by tall Eucalyptus forest and evaluate post-fire recovery after a large wildfire burned the area in 2019.Methods
We mapped historical vegetation changes by analysing sequences of aerial photography from 1947 to 2010, and in 2020 used UAS LiDAR to geolocate the current forest boundary. Satellite imagery, field measures of char: canopy height ratio, and stem mortality were used to gauge fire severity, while vegetative and seedling regeneration were used to assess post-fire recovery.ResultsForest-sedgeland boundaries were stable over the 73-year period. Sedgeland and scrub communities experienced high severity fires, reflecting their low stature compared to taller forest, which suffered minimal canopy impact. The dominant sedge and tree species in the three communities were post-fire resprouters, resulting in rapid recovery of vegetation structure, with prolific seeding of species killed by the fire.Conclusion
Forest-sedgeland boundaries in western Tasmania are resilient to fire because of keystone resprouter species, and geographically stable in historical time frames, a finding inconsistent with the FMASS model. Our study contributes to global question of treeless area in climate zones suitable for forest.
Interactions between rainforest plants and fire occur when fires encroach into rainforest and when rainforest pioneers colonise fire-prone open forests. Although numerous studies show that many rainforest plants survive fire by resprouting and postfire seedling recruitment, data is lacking for several major Australian rainforest types. In this study, we examine fire-resilience traits among 228 taxa of woody rainforest plants in four rainforest classes (subtropical, warm temperate, dry and littoral rainforest) less than 1 year after being burnt in the extensive wildfires of 2019-20. Among taxa with ≥ 5 records of complete crown scorch (126), resprouting occurred in 63% of taxa overall and 61% of late-successional taxa. Fire-cued seedling recruitment occurred in 62% of taxa overall and 48% of late-successional taxa. Surprisingly, species richness of woody plants increased 22% postfire due to high rates of persistence and emergence of new taxa into standing plant populations as seedlings. Stem density increased ~400% postfire due to high rates of resprouting and reproduction through suckering and seedling recruitment, although there was a significant redistribution from medium to smaller stem size classes. Larger stems (>10 cm DBH) were not significantly reduced in rainforest stands. High resprouting rates in small rainforest plants (1 cm DBH, 1m tall) suggests rapid attainment of resprouting capacity. Our findings demonstrate that most subtropical, dry, warm temperate and littoral rainforest plant taxa are resilient to rare fires, and suggest that rainforest plants that invade rarely-burnt open forests may quickly become resistant to removal by infrequent fires, with potential for increased populations through fire-enhanced seedling germination.
Seed banking of rainforest species is hindered by lack of knowledge as to which species are tolerant of desiccation and freezing. We assessed 313 Australian rainforest species for seed banking suitability by comparing the germination percentage of fresh seeds to seeds dried at 15% RH and seeds stored at −20 °C after drying. We then compared desiccation responses to environmental, habit, fruit and seed characteristics to identify the most useful predictors of desiccation sensitivity. Of 162 species with ≥ 50% initial germination, 22% were sensitive to desiccation, 64% were tolerant and 10% were partially tolerant; the responses of 4% were uncertain. Of 107 desiccation tolerant species tested for response to freezing, 24% were freezing sensitive or short-lived in storage at −20 °C. Median values for fresh seed moisture content (SMC), oven dry weight (DW) and the likelihood of desiccation sensitivity (PD-S) were significantly greater for desiccation sensitive than desiccation tolerant seeds. Ninety-four to 97% of seeds with SMC < 29%, DW < 20 mg or PD-S < 0.01 were desiccation tolerant. Ordinal logistic regression of desiccation response against environmental, habit, fruit and seed characteristics indicated that the likelihood of desiccation sensitivity was significantly increased by a tree habit, fleshy fruit, increasing fresh SMC and increasing PD-S. The responses observed in this study were combined with earlier studies to develop a simple decision key to aid prediction of desiccation responses in untested rainforest species.
The use of traits is growing in ecology and biodiversity informatics, with initiatives to collate trait data and integrate it into biodiversity databases. A need to develop better predictive capacity for how species respond to environmental change has in part motivated this focus. Functional traits are of most interest—those with a defined link to individual survival, development, growth and reproduction.
Non‐trivial challenges arise immediately in deciding which functional traits to prioritise and how to characterise them. Here we discuss the advantages of a theoretical perspective for defining functional traits in the context of dynamical systems models of energy and mass exchange that link organisms to their environments. We argue that the theoretical frameworks upon which such models are built (biophysical ecology, metabolic theory) provide clear criteria to decide upon functional trait definitions, measurement requirements and associated metadata, via their mathematical connection to model parameters and state variables, and thus to system performance (survival, development, growth and reproduction).
We distinguish ‘descriptive’ traits from ‘functional’ traits by dividing the latter into four classes—parameter, model, threshold and estimation—according to whether they are model parameters, define model structure, are threshold state variables or can be used to estimate model parameters.
We develop a decision tree for this classification and illustrate it in the context of mammalian heat exchange but emphasise the scheme's generality to any kind of organism.
We show how a theoretical perspective may change how we prioritise traits for collection and databasing in ways that are not necessarily more difficult to achieve, especially with new technologies, and provide clear guidance for requisite metadata. The use of theoretically driven criteria for prioritising the collection of functional trait data will maximise the generality, quality and consistency of trait databases for comparative analyses. Such databases will simultaneously facilitate the development of integrated predictive modelling frameworks across multiple organisational scales from individuals to ecosystems.
A free Plain Language Summary can be found within the Supporting Information of this article.
Over the past few decades there has been a growing realization that a large share of apparently ‘virgin’ or ‘old-growth’ tropical forests carries a legacy of past natural or anthropogenic disturbances that have a substantial effect on present-day forest composition, structure and dynamics. Yet, direct evidence of such disturbances is scarce and comparisons of disturbance dynamics across regions even more so. Here we present a tree-ring based reconstruction of disturbance histories from three tropical forest sites in Bolivia, Cameroon, and Thailand. We studied temporal patterns in tree regeneration of shade-intolerant tree species, because establishment of these trees is indicative for canopy disturbance. In three large areas (140–300 ha), stem disks and increment cores were collected for a total of 1154 trees (>5 cm diameter) from 12 tree species to estimate the age of every tree. Using these age estimates we produced population age distributions, which were analyzed for evidence of past disturbance. Our approach allowed us to reconstruct patterns of tree establishment over a period of around 250 years. In Bolivia, we found continuous regeneration rates of three species and a peaked age distribution of a long-lived pioneer species. In both Cameroon and Thailand we found irregular age distributions, indicating strongly reduced regeneration rates over a period of 10–60 years. Past fires, windthrow events or anthropogenic disturbances all provide plausible explanations for the reported variation in tree age across the three sites. Our results support the recent idea that the long-term dynamics of tropical forests are impacted by large-scale disturbance-recovery cycles, similar to those driving temperate forest dynamics.
Postfire resprouting and recruitment from seed are key plant life-history traits that influence population dynamics, community composition and ecosystem function. Species can have one or both of these mechanisms. They confer resilience, which may determine community composition through differential species persistence after fire. To predict ecosystem level responses to changes in climate and fire conditions, we examined the proportions of these plant fire-adaptive traits among woody growth forms of 2880 taxa, in eight fire-prone ecosystems comprising ~87% of Australia's land area. Shrubs comprised 64% of the taxa. More tree (>84%) than shrub (~50%) taxa resprouted. Basal, epicormic and apical resprouting occurred in 71%, 22% and 3% of the taxa, respectively. Most rainforest taxa (91%) were basal resprouters. Many trees (59%) in frequently-burnt eucalypt forest and savanna resprouted epicormically. Although crown fire killed many mallee (62%) and heathland (48%) taxa, fire-cued seeding was common in these systems. Postfire seeding was uncommon in rainforest and in arid Acacia communities that burnt infrequently at low intensity. Resprouting was positively associated with ecosystem productivity, but resprouting type (e.g. basal or epicormic) was associated with local scale fire activity, especially fire frequency. Although rainforest trees can resprout they cannot recruit after intense fires and may decline under future fires. Semi-arid Acacia communities would be susceptible to increasing fire frequencies because they contain few postfire seeders. Ecosystems dominated by obligate seeders (mallee, heath) are also susceptible because predicted shorter inter-fire intervals will prevent seed bank accumulation. Savanna may be resilient to future fires because of the adaptive advantage of epicormic resprouting among the eucalypts. The substantial non-resprouting shrub component of shrublands may decline, but resilient Eucalyptus spp. will continue to dominate under future fire regimes. These patterns of resprouting and postfire seeding provide new insights to ecosystem assembly, resilience and vulnerability to changing fire regimes on this fire-prone continent.
Crown Copyright © 2015. Published by Elsevier B.V. All rights reserved.
The relative ability of sprouting and nonsprouting chaparral shrubs to recover from fire was studied by examining population of congeneric pairs of species in burned and adjacent unburned areas. The pairs of species selected, with the nonsprouting species named first, were Arctostaphylos glauca - A. glandulosa and Ceanothus greggii - C. leucodermis. Data were also obtained on certain associated species, particularly Adenostoma fasciculatum. The numbers, sizes and condition of the component species at each of the sites were measured. Both sprouting and nonsprouting species showed vigorous recovery from fire. It seemed likely that the burned stands would eventually reach a state of development comparable to that shown in the preburn stand without any significant shifts in composition Mortality of shrubs resulting from the fire was complete for nonsprouters but varied in sprouting species. In some there was essentially no mortality, while in others, especially Adenostoma, it was rather high. Seedling establishment in the shrub species varied markedly and seemed to be correlated with the degree of fire-caused mortality. A profound difference was observed in the life histories of the two nonsprouting shrubs. Whereas Ceanothus greggii produced a very high number of seedlings after fire, Arctostaphylos glauca produced substantially fewer. A comparison of the density-size distribution of live and dead stems indicated that C. greggii suffers high mortality early in succession, but A. glauca loses very few individuals even after 90 years without fire. In light of these results a model is proposed which we believe explains the adaptive significance of the obligate-seeding strategy in the southern California chaparral.
Juvenile (2–4 years old) plants of a taxonomically diverse range of dicotyledonous species were examined following recruitment from seed in recently burnt habitats in S.W. Australia. Obligate seeder species (those succumbing to fire) had on average, an almost threefold greater total plant d. wt and more than a fourfold greater shoot: root d. wt ratio than comparably-aged, cohabiting, resprouter species (those capable of surviving fire). Starch was generally much more concentrated in root dry matter of resprouters than seeders, and both categories exhibited greater starch storage capacity in roots than shoots. Members of the Myrtaccae were exceptional in not showing a greater root starch reserve in resprouter than in seeder species. and in carrying as high, or higher, starch levels in shoots as in roots. Anatomical investigations on roots provided instances of zero starch storage, storage, only in rays or in cortex, in rays and in xylem parenchyma, in rays and in cortex, or in all three locations. High starch ratings of resprouter roots related mostly to higher starch grain packing density at storage sites, but in certain instances these also reflected proportionally greater areas of tissue specifically devoted to storage. Dry matter of shoots of both seeders and resprouters generally contained higher levels of N, P, K, Ca and Mg than that of roots, but there was no significant evidence of elements being more concentrated in resprouters than in seeders.
The role of fire in governing rainforest–eucalypt forest ecotone dynamics is of theoretical interest and has conservation management implications. Several eucalypt forests in the Wet Tropics of Australia have an endangered status due to extensive conversion to rainforest. Rainforest plants are known to survive occasional low intensity fires in the eucalypt forest ecotone. However, the ability of rainforest plants to survive frequent fires remains untested. The timing of rainforest expansion is also a subject of interest, and is generally considered to be delayed until fire has been absent for several years. We used 14 years of data collected across 13 plots in the Wet Tropics of north‐eastern Australia to test predictions regarding rainforest seedling recruitment and post‐fire regenerative capacity. The 13 plots received different numbers of fires, between zero and five, over the 14‐year study. The recruitment of new rainforest plants in the ecotone was most abundant in the initial year after fire. If this post‐fire pulse of recruitment is left undisturbed, it can facilitate the subsequent germination of additional rainforest species. The removal of grass cover, whether temporarily in the immediate post‐fire environment or once a developing rainforest mid strata shades out grasses, appears crucial to abundant rainforest recruitment. A variety of tropical rainforest species can persist under a frequent fire regime through resprouting. The difference in the mode of resprouting, between ground‐level coppicing rainforest plants and canopy resprouting eucalypt forest trees, is the critical mechanism that causes regular fire to maintain an open structure in eucalypt forests. The inability of rainforest species to maintain their height when fires fully scorch their crowns, temporarily resets the forest's open structure and delays the rainforest's ability to dominate through shading out grasses to transform the ecosystem into a closed forest.
Post-fire seedling recruitment was studied at six heathland sites near Evans
Head, north-eastern NSW, in a range of habitats from dry to wet sand-heath.
Species fire responses were recorded and seedling density, seedling survival
and seedling shoot-growth rate were monitored for 3 years. There were marked
differences in total seedling density and survivorship in different habitats,
caused by several possible factors. Obligate seeders and facultative
resprouters were found to have overlapping yet broadly distinctive patterns of
seedling recruitment behaviour. Facultative resprouters as a group had
significantly lower levels of seedling density and survival than obligate
seeders. Six species exhibited ecotypic variation in mode of regeneration,
five accompanied by marked changes in seedling density. Patterns of seedling
recruitment behaviour in relation to fire response and habitat were consistent
with the theory that resprouting is a stress-tolerant regeneration strategy
and that for a given species regeneration strategy is linked with habitat
quality.
Using pre- and post-fire satellite imagery from SPOT2, we examined the fire severity and intensity of the Christmas 2001 wildfires in the greater Sydney Basin, Australia. We computed a Normalised Difference Vegetation Index (NDVI) from the two satellite images captured before ( November 2001) and after ( January 2002) the wildfires, then subtracted the later from the former to produce a difference image (NDVIdiff) which was subsequently classified into six fire severity classes (unburnt, low, moderate, high, very high and extreme severity). We then tested the fire severity classification on 342 sample sites within the 225 000 ha fire affected area using a qualitative visual assessment guide. We found that the NDVIdiff classification produced an accuracy of at least 88% (K-hat = 0.86), with the greatest discrepancy being between the low and moderate classification. Knowledge of rate of spread over some of the affected area, coupled with a complete knowledge of fuel loads, was used to retrospectively model fire intensity, which in areas of extreme fire intensity, produced heat energy levels exceeding 70000 kWm(-1). Importantly, we found no positive effect of topography on fire severity, in fact finding an inverse relationship between slope and fire severity and no effect due to aspect. Further analysis showed that flat to moderate slopes less than 18. across all aspects suffered the greatest vegetal destruction, and there was no relationship between north-westerly aspects and fire severity. We also introduce a relatively simple method for estimating fuel load biomass using a combination of satellite image and rapid field assessment. We found 79% accuracy for this method based on 125 sample sites. It is postulated that this type of analysis can greatly improve our understanding of the spatial impact of fire, how natural areas within the fire ground were impacted, and how remote sensing and GIS technologies can be efficiently used in fire management planning and post-fire analysis.
Cyclones are relatively infrequent, may cause massive and widespread disturbance to tropical regions, and are recognized as important determinants of the structure of tropical rainforest communities. Climate change scientists predict that the intensity of cyclones will increase in the future; understanding the long-term implications of these major disturbances for tropical forest composition and structure will be vital in anticipating and adapting to future changes and impacts. We established a long-term monitoring site in a rainforest area impacted by severe tropical Cyclone Larry which crossed the North Queensland coast of Australia in March 2006. We monitored recruitment, growth and mortality of nearly 17 000 seedlings in 90 quadrats across the study area for almost 5 years following the cyclone and measured the impact of variation in cyclone disturbance and debris load on community diversity, composition and dispersion as the forest recovered. We show that the level of structural disturbance sustained by the forest has a strong and immediate influence on community dynamics. Quadrats in severely disturbed areas, which were characterized by multiple treefalls and extensive canopy loss, had higher levels of diversity and variation in community assemblage than quadrats in areas characterized primarily by branch loss and defoliation. A rapid divergence in community composition between quadrats in the most- and least-severely disturbed areas resulted in the development of statistically distinct community states across relatively small scales. This provides further evidence that severe cyclones are important in maintaining species diversity in tropical forests.
Ecological theory differentiates rainforest and open vegetation in many regions as functionally divergent alternative stable states with transitional (ecotonal) vegetation between the two forming transient unstable states. This transitional vegetation is of considerable significance, not only as a test case for theories of vegetation dynamics, but also because this type of vegetation is of major economic importance, and is home to a suite of species of conservation significance, including the world's tallest flowering plants. We therefore created predictions of patterns in plant functional traits that would test the alternative stable states model of these systems. We measured functional traits of 128 trees and shrubs across tropical and temperate rainforest - open vegetation transitions in Australia, with giant eucalypt forests situated between these vegetation types. We analysed a set of functional traits: leaf carbon isotopes, leaf area, leaf mass per area, leaf slenderness, wood density, maximum height and bark thickness, using univariate and multivariate methods. For most traits, giant eucalypt forest was similar to rainforest, while rainforest, particularly tropical rainforest, was significantly different from the open vegetation. In multivariate analyses, tropical and temperate rainforest diverged functionally, and both segregated from open vegetation. Furthermore, the giant eucalypt forests overlapped in function with their respective rainforests. The two types of giant eucalypt forests also exhibited greater overall functional similarity to each other than to any of the open vegetation types. We conclude that tropical and temperate giant eucalypt forests are ecologically and functionally convergent. The lack of clear functional differentiation from rainforest suggests that giant eucalypt forests are unstable states within the basin of attraction of rainforest. Our results have important implications for giant eucalypt forest management.
Aim
Our aims were to identify centres of endemism and to infer whether these
areas have functioned as refugia for subtropical rain forest plants through his-
torical climate fluctuations.
Location
Subtropical eastern Australia (23–33° S; 145–155° E).
Methods We collated 25,000 records of 179 endemic rain forest plants to
identify geographical areas with unusually high concentrations of endemic taxa
and range-restricted endemics. We then tested whether centres of endemism
coincide with other features indicating refugia, including habitat stability over
120,000 years, and we related dispersal patterns to past habitat stability using
seed weight as a surrogate for dispersal ability of endemic plant taxa.
Results
We identified five main centres of endemism. Historical stability and
other processes affecting diversity, including current rainfall, rain forest area,
and topographic complexity, explained 58% of variation in plant-weighted
endemism. Taxa with poor dispersal ability were concentrated in the areas that
were most stable historically.
Main conclusions
Several lines of evidence suggest that centres of endemism
have functioned as important refugia for subtropical rain forest taxa through
historical climate fluctuations. The highest concentrations of range-restricted
endemic species occur in locations that are predicted to have maintained stable
rain forest habitat over at least the past 120,000 years. This association was
independent from other factors that were expected to promote diversity (i.e.
rain forest area and current environmental suitability). These locations have
disproportionately high concentrations of species with poor dispersal ability
(large-seeded species).
A comparative study of vegetation responses to. re and drought investigated whether species regeneration mode, seedling density response (SDR) and seedling shoot growth rate varied significantly in relation to disturbance agent (fire and drought), habitat type (rock-outcrop and fringing vegetation) and plant growth form. A three-way ANOVA showed that SDR varied significantly in relation to all three categorical variables and most strongly in relation to disturbance agent. Seeders comprised 87% of the post-fire flora and 99.3% of the peak seedling population in rock-outcrop habitat, while resprouters were much more prominent in fringing woodland. Species SDRs and seedling growth rates were generally much higher after. re. Fire produced a high SDR with high shrub, grass and ephemeral therophyte components, and drought produced a low SDR dominated by grasses and herbs and inhibited shrub and ephemeral recruitment. Post-fire obligate-seeder shrubs behaved as facultative resprouters after drought. Some species exhibited SDRs equivalent to fire and drought, others appeared to require. re for regeneration, while others recruited more successfully after drought. This spectrum of responses indicated a range of optimal disturbance environments, depending on species, which was only partly consistent with the hypothesis that species exhibit essentially the same life-history syndromes in response to fire and drought. The dominance of seeders in outcrop vegetation appeared to be related to skeletal soil, higher disturbance frequency and soil trophic conditions, rather than low. re frequency.
An area of rain forest burnt in the Zeehan fire of 1981 is regenerating toward pure rain forest. This fire was small and patchy and therefore many trees survived to provide a seed source for a major germination of rain forest species after the fire. However, several seral stages are expected to precede the climax vegetation. In contrast, an area of mixed forest burnt in the Savage River fire of 1982 has undergone a major change in species composition because of the proximity of a sclerophyll seed source. The Eucalyptus nitida overstorey is likely to be maintained, but sclerophyllous species will probably increase in dominance in the understorey at the expense of the pre-fire rain forest dominance. Given a long, fire-free interval, this forest may undergo succession to the climax rain forest, but this is unlikely due to large amounts of fuel, the drying effect of the forest edge, and the nearby road which allows access for human-caused fires.
One way species of low maximum height can accrue sufficient light income to persist in vegetation is via rapid height growth immediately following disturbance. By surveying patches of known time since fire, we reconstructed height–growth trajectories for 19 post-fire recruiting species from fire-prone vegetation in south-eastern Australia. Cross-species patterns of height growth were compared to several plant traits thought to influence height strategy, including leaf mass per area, stem tissue density, stem diameter and capacity to resprout. Shorter species were found to temporarily outpace taller species, both as resprouters and within reseeders. Among reseeders, a single axis of variation summarised patterns of height–growth, time to onset of reproduction and longevity. This axis was tightly correlated with maximum height, leaf mass per area and stem diameter at a given height. These results illustrate how a range of height strategies can coexist in fire-prone vegetation, via the time-process initiated by disturbance.
Aim The mesic biome, encompassing both rain forest and open sclerophyllous forests, is central to understanding the evolution of Australia’s terrestrial biota and has long been considered the ancestral biome of the continent. Our aims are to review and refine key hypotheses derived from palaeoclimatic data and the fossil record that are critical to understanding the evolution of the Australian mesic biota. We examine predictions arising from these hypotheses using available molecular phylogenetic and phylogeographical data. In doing so, we increase understanding of the mesic biota and highlight data deficiencies and fruitful areas for future research.
The laurel-forest of the Canary Islands is a montane cloud-forest. In order to gain some knowledge on the processes that maintain tree species diversity, we conducted an analysis of three different laurel-forest plots of the Anaga massif (Tenerife), varying in canopy composition but growing under similar environmental conditions. For each plot we recorded basal area of the canopy trees (h1.30 m), as well as seed-bank composition. The plots have similar regeneration composition, which appears to be independent of differences in canopy composition. Laurus azorica is the most common seedling species, whereas Prunus lusitanica is the most abundant species among suckers and basal shoots. Neither Erica arborea nor Myrica faya, the two main canopy trees in one of the plots, were found in any of the stands as seedlings or suckers, despite their existence as viable seeds in the seed-bank. The regeneration composition and the canopy composition in one of the plots is remarkable different, revealing differents dynamics processes in the three plots. The results suggest the existence of three well-defined ecological groups: pioneer (regeneration primarily by seedlings), non-pioneer (regeneration by seedlings and suckers) and remnant species (regeneration primarily by suckers).These three groups and the effect of small scale disturbances (natural and human-induced), could help to understand the maintenance of tree species richness.
A new method is presented for assessment of compositional changes in disturbed savanna systems and for identification of species susceptible to local extinction. Such information is urgently needed as a basis for management plans that aim at ensuring conservation and sustainable use of savanna vegetation. Size class distributions (SCDs) of trees and shrubs from a fire-disturbed savanna in Senegal are analysed and compared to observations provided by local people on declining species. Many species, particularly large trees, have few young individuals and therefore flat SCDs that deviate from the reverse-J shape SCD characterizing species with abundant and constant rejuvenation. Based on comparisons of SCDs with local information and historical records, it is concluded that most of the flat distributions analysed are effects of declining population sizes caused by human impact, particularly fire. Results from the analyses certify that a change in species composition from a vegetation characterized by large trees to one dominated by shrubs takes place. Whereas most of the declining species are locally appreciated, this is not the case for the few species with good rejuvenation. Therefore, if the observed trend continues, it will have severe implications for the local communities.
Tropical rain forest expansion and savanna woody vegetation thickening appear to be a global trend, but there remains uncertainty about whether there is a common set of global drivers. Using geographic information techniques, we analyzed aerial photography of five areas in the humid tropics of northeastern Queensland, Australia, taken in the 1950s and 2008, to determine if changes in rain forest extent match those reported for the Australian monsoon tropics using similar techniques. Mapping of the 1950s aerial photography showed that of the combined study area (64,430 ha), 63% was classified as eucalypt forests/woodland and 37% as rain forest. Our mapping revealed that although most boundaries remained stable, there was a net increase of 732 ha of the original rain forest area over the study period, and negligible conversion of rain forest to eucalypt forest/woodland. Statistical modeling, controlling for spatial autocorrelation, indicated distance from preexisting rain forest as the strongest determinant of rain forest expansion. Margin extension had a mean rate across the five sites of 0.6 m per decade. Expansion was greater in tall open forest types but also occurred in shorter, more flammable woodland vegetation types. No correlations were detected with other local variables (aspect, elevation, geology, topography, drainage). Using a geographically weighted mean rate of rain forest margin extension across the whole region, we predict that over 25% of tall open forest (a forest type of high conservation significance) would still remain after 2000 years of rain forest expansion. This slow replacement is due to the convoluted nature of the rain forest boundary and the irregular shape of the tall open forest patches. Our analyses point to the increased concentration of atmospheric CO2 as the most likely global driver of indiscriminate rain forest expansion occurring in northeastern Australia, by increasing tree growth and thereby overriding the effects of fire disturbance.
Natural disturbances have been traditionally defined in terms of major catastrophic events originating in the physical environment and, hence, have been regarded as exogenous agents of vegetation change. Problems with this view are: (1) there is a gradient from minor to major events rather than a uniquely definable set of major catastrophes for each kind of disturbance, and (2) some disturbances are initiated or promoted by the biotic component of the system. Floras are rich in disturbance-adapted species. Disturbances have probably exerted selective pressure in the evolution of species strategies. Heathland cyclic successions and gap-phase dynamics in forests have been viewed as endogenous patterns in vegetation. When death in older individuals imposes a rhythm on community reproduction, dynamics may indeed be the result of endogenous factors. However, documented cases of senescence in perennial plants are few and many cyclic successions and cases of gap-phase dynamics are initiated by physical factors. Forest dynamics range from those that are the result of individual tree senescence and fall, through those that are the result of blowdown of small groups of healthy trees, to those that are the result of large wind- storms which level hectares of forest. The effect of wind ranges from simple pruning of dead plant parts to widespread damage of living trees. Wind speed is probably inversely proportional to occurrence frequency. Disturbances vary continuously. There is a gradient from those community dynamics that are initiated by endogenous factors to those initiated by exogenous factors. Evolution has mediated between species and environment; disturbances are often caused by physical factors but the occurrence and outplay of disturbances may be a function of the state of the community as well.
Mediterranean-type ecosystems are among the most remarkable plant biodiversity "hot spots" on the earth, and fire has traditionally been invoked as one of the evolutionary forces explaining this exceptional diversity. In these ecosystems, adult plants of some species are able to survive after fire (resprouters), whereas in other species fire kills the adults and populations are only maintained by an effective post-fire recruitment (seeders). Seeders tend to have shorter generation times than resprouters, particularly under short fire return intervals, thus potentially increasing their molecular evolutionary rates and, ultimately, their diversification. We explored whether seeder lineages actually have higher rates of molecular evolution and diversification than resprouters. Molecular evolutionary rates in different DNA regions were compared in 45 phylogenetically paired congeneric taxa from fire-prone Mediterranean-type ecosystems with contrasting seeder and resprouter life histories. Differential diversification was analyzed with both topological and chronological approaches in five genera (Banksia, Daviesia, Lachnaea, Leucadendron, and Thamnochortus) from two fire-prone regions (Australia and South Africa). We found that seeders had neither higher molecular rates nor higher diversification than resprouters. Such lack of differences in molecular rates between seeders and resprouters-which did not agree with theoretical predictions-may occur if (1) the timing of the switch from seeding to resprouting (or vice versa) occurs near the branch tip, so that most of the branch length evolves under the opposite life-history form; (2) resprouters suffer more somatic mutations and therefore counterbalancing the replication-induced mutations of seeders; and (3) the rate of mutations is not related to shorter generation times because plants do not undergo determinate germ-line replication. The absence of differential diversification is to be expected if seeders and resprouters do not differ from each other in their molecular evolutionary rate, which is the fuel for speciation. Although other factors such as the formation of isolated populations may trigger diversification, we can conclude that fire acting as a throttle for diversification is by no means the rule in fire-prone ecosystems.
Until recently, few people would have associated rainforest with Australia. The present-day distribution of Australian rainforest is limited but it was formerly more widespread and was the dominant vegetation type of the entire continent. The contraction to its present limits reflects environmental changes that have taken place over many millions of years. In this book Dr Adam gives a general account of the Australian rainforests: what they are, where they are, and how their present distribution has evolved. His aim is to provide a broad framework that will enable new results to be placed in context. The book concludes with a historical account of human interaction with the rainforest from late Pleistocene times to the 1980s. The history of the exploitation of the Australian rainforests and the development of a conservation ethic have important lessons for the conservation of rainforests world-wide.
The vulnerability to repeated high severity fires of tall wet eucalypt forests (TWEF) dominated by obligate seeder species is widely understood. However, 80% of Tasmania’s TWEF are dominated by resprouter species, and while these forests are more resilient to wildfire than those dominated by obligate seeders, the degree of their resilience is not well documented. Recently, two wildfires affected five 1-ha forest plots that had been previously measured, providing the opportunity to assess fire effects on these forest stands. We characterised these wildfires using remote sensing and field measurements of char height (a proxy for fire intensity) and canopy scorch (fire severity). We assessed the influence of tree diameter, fire intensity and seedling densities on the survival and resprouting responses of eucalypt overstorey trees and mixed species understorey trees. Our results showed that these fires were predominantly of low to moderate intensity and severity. Our results showed that mature TWEF were resilient to these wildfires, with overall eucalypt survival of 75%. The major eucalypt species were either mostly not defoliated (E. regnans), or could recover rapidly by epicormic resprouting (E. delegatensis and E. obliqua). Results from this and other studies show recovery from topkill caused by high severity fires occurs but is slower, by basal resprouting (E. obliqua) or from seed (all species). By contrast, understorey species suffered high mortality (85% overall), with few species showing substantial resprouting. Fire resistance in both groups increased markedly with tree diameter.
Our results have implications for forest management. The high survival of overstorey eucalypts leads to a multi-aged stand structure in most unlogged old growth TWEF in Tasmania. On the other hand, clearfell logging, originally designed to mimic stand replacing wildfire in obligate seeder systems, creates a vulnerable, even aged stand of young regrowth, and at a landscape scale, it also reduces average tree size, reducing overall resistance to fire. Adopting alternatives to clearfelling, such as partial logging systems, will increase landscape resilience to fire, as well as providing other previously shown benefits.
Wet sclerophyll forests (WSFs) are dominated by sclerophyllous trees (Eucalyptus and closely allied genera; family Myrtaceae) usually taller than 30 m at maturity in areas of greater than 1 000 mm of annual rainfall. They include the tallest angiosperms, and exhibit biomass amongst the highest in terrestrial ecosystems. Although occupying only 0.75% of Australia’s land-cover (4.83 million ha), the environmental, economic and cultural significance of WSF is far out of proportion to their distributional area. They occur discontinuously in a zone of high rainfall from north-eastern Queensland to southern Tasmania, with an outlier in south-western Australia; and also occur in east Malesia. In moist or protected margins in eastern Australia (and Malesia), and more extensively in Tasmania, mature eucalypts may occur above a well-developed rainforest; and are sometimes classified separately as mixed forest. This contrasts with WSF in south-western Australia, which includes no rainforest trees. Wet sclerophyll forest grades into rainforest in wetter, more fertile, or less frequently burnt margins; and into dry sclerophyll forests and woodlands in drier, more seasonal, less fertile, more frequently burnt, or cooler sites. Boundaries to adjacent forest types may be sharp, but sometimes unstable in eastern Australia, depending on disturbance history. These forests include important refugia under climate change, harbouring a diverse biota, featuring many endemic taxa. However, they are impacted by climate disruption and associated changes in fire regime, and distributions of weed and pest taxa. As a result, there are conservation concerns for the old-growth elements that are unique to these systems.
Provides a synoptic description of the forests, with particular reference to the various eucalyptus species, and key environmental factors are identified. Fires in the upper canopy, undergrowth, litter, peat and soil-humus are described, and the effects of burning indicated. Pyric succession is noted, indicating the rich herb vegetation characteristic of the initial post-burn years, and the wet schlerophyll strategy is outlined. It seems paradoxical that forests producing vast amounts of fuel and generating the fiercest fires consist of fire-sensitive species, although the fact that they need to be burned at some time in their seed-bearing life is axiomatic. -P.J.Jarvis
Plant traits considered adaptive to fire may be distinguished by: their vegetative survival; enhanced reproduction through fire-stimulated disperal; or enhanced reproduction facilitated by in-soil storage with fire-stimulated germination. A single trait, eg. vegetative survival and resprouting, or hard-seededness, may be adaptive not only to fires but also to other variables. Different species in the same environment may have different adaptive traits but persist with equal success. Adaption must be considered in terms of the fire regime: type, season, frequency and intensity. Traits enabling survival and reproduction during a succession of fires must also enable survival and reproduction to take place during stresses imposed by other selective agents, eg. drought. -from Author
The importance of dormant buried seeds of understorey species of the wet sclerophyll forests of northern N.S.W. is discussed in relation to their germination ability following fire or mechanical or chemical abrasion.
Estimation of tree age in various species along the east coast of Australia is made difficult by the lack of identifiable annual growth rings in stem wood and this creates problems in studying long term forest dynamics. It is possible to use radiocarbon dating to obtain general information for this purpose. In an area on the north coast of New South Wales where three forest types, were in close proximity, individuals of Eucalyptus pilularis (blackbutt) were found to be about 100 years old, Tristania conferta (brushbox) between 100 and 1340 years old and subtropical rainforest was between 100 and 880 years old. From these data, together with that from dating of soil charcoal, the frequency of fire (with sufficient severity to result in the production of charcoal) was estimated to be 300 years in the blackbutt forest, 300–400 years in the brushbox forest and in excess of 1000 years in the rainforest. Although only a few results are available, they indicate the potential of radiocarbon dating for use in studies on long term dynamics of forest ecosystems.
We used a mosaic of infrequently burnt temperate rainforest and adjacent, frequently burnt eucalypt forests in temperate eastern Australia to test whether: (1) there were differences in flammability of fresh and dried foliage amongst congeners from contrasting habitats, (2) habitat flammability was related to regeneration strategy, (3) litter fuels were more flammable in frequently burnt forests, (4) the severity of a recent fire influenced the flammability of litter (as this would suggest fire feedbacks), and (5) microclimate contributed to differences in fire hazard amongst habitats. Leaf-level comparisons were made among 11 congeneric pairs from rainforest and eucalypt forests. Leaf-level ignitability, combustibility and sustainability were not consistently higher for taxa from frequently burnt eucalypt forests, nor were they higher for species with fire-driven recruitment. The bulk density of litter-bed fuels strongly influenced flammability, but eucalypt forest litter was not less dense than rainforest litter. Ignitability, combustibility and flame sustainability of community surface fuels (litter) were compared using fuel arrays with standardized fuel mass and moisture content. Forests previously burned at high fire severity did not have consistently higher litter flammability than those burned at lower severity or long unburned. Thus, contrary to the Mutch hypothesis, there was no evidence of higher flammability of litter fuels or leaves from frequently burnt eucalypt forests compared with infrequently burnt rainforests. We suggest the manifest pyrogenicity of eucalypt forests is not due to natural selection for more flammable foliage, but better explained by differences in crown openness and associated microclimatic differences.
Alternative stable state theory is often used to explain the occurrence of flammable vegetation adjacent to less flammable vegetation where fire regimes mediate the shift between states. In 2002 an extreme landscape scale fire burnt extensive areas of forests in eastern Australia, including rainforests that are rarely severely burnt. This unique event allowed us to test long-held assumptions that predict landscape scale change after major disturbance. We tested three assumptions for detecting alternative community states; (1) that the scale of the event was large enough to remove canopy dominants, (2) fire feedbacks, both positive and negative are present, and (3) shifts in the floristic composition of communities are detected. We also examined whether high severity fires resulted in a community shift from less flammable to more flammable vegetation (e.g. from rainforest to wet sclerophyll vegetation), by examining floristic composition of vegetation communities (rainforest, wet sclerophyll forest, and dry sclerophyll forest) when burnt at different fire severities (high and low). Conversely, we tested whether there was a state shift from flammable to less flammable vegetation communities in sclerophyll forests long unburnt. In addition, we determined if there was any evidence that antecedent fire regimes and fire severity influenced flammability feedbacks.
Disturbance is a dominant factor in many ecosystems, and the disturbance regime is likely to change over the next decades in response to land-use changes and global warming. We assume that predictions of vegetation dynamics can be made on the basis of a set of life-history traits that characterize the response of a species to disturbance. For crown-fire ecosystems, the main plant traits related to postfire persistence are the ability to resprout (persistence of individuals) and the ability to retain a persistent seed bank (persistence of populations). In this context, we asked (1) to what extent do different life- history traits co-occur with the ability to resprout and/or the ability to retain a persistent seed bank among differing ecosystems and (2) to what extent do combinations of fire- related traits (fire syndromes) change in a fire regime gradient? We explored these questions by reviewing the literature and analyzing databases compiled from different crown-fire ecosystems (mainly eastern Australia, California, and the Mediterranean basin). The review suggests that the pattern of correlation between the two basic postfire persistent traits and other plant traits varies between continents and ecosystems. From these results we predict, for instance, that not all resprouters respond in a similar way everywhere because the associated plant traits of resprouter species vary in different places. Thus, attempts to generalize predictions on the basis of the resprouting capacity may have limited power at a global scale. An example is presented for Australian heathlands. Considering the com- bination of persistence at individual (resprouting) and at population (seed bank) level, the predictive power at local scale was significantly increased.
Woody plants may be killed by severe disturbance or resprout from vegetative tissue. Sprouters can persist at a site through several generations of nonsprouters. Differences in sprouting behavior are therefore important for understanding vegetation dynamics, extinction risks, and woody plant management. Although sprouting appears not to be uniquely correlated with many other intrinsic attributes, such as specific leaf area or breeding systems, a clear correlate is reduced seedling aboveground growth rates from sprouters allocating more to belowground structures. Consequently, sprouters tend to have low seedling recruitment rates, and saplings take longer to reach maturity. Sprouters also tend to have lower seed output than nonsprouters, but comparative studies have seldom taken other trait differences such as plant size into account. Added to these trade-offs between persistence and recruitment, sprouters are often multistemmed and shorter than related nonsprouters and may be outcompeted by them when disturbances are rare. Since sprouters tend to have long generation times, damped demographic trends, and gene flow across generations, it has been suggested that their speciation rates would be low. The available data, primarily from fire-prone Gondwanan shrublands in South Africa, show no strong differences in speciation rates of related sprouters versus seeders. This indicates that ecological factors are important determinants of the evolution of fire life histories. Analysis of disturbance regimes indicates a fundamental ecological correlate: sprouters are favored where disturbance regimes are frequent and severe in comparison to regrowth rates. To bridge the gap between ecology and evolution, data are needed on the genetical differences between related species with contrasting sprouter life histories.
Following an introduction of the Australian environment, the remaining chapters examine: definition and classification of rain forest; an overview of Australian rain forests; rain forest boundaries and the problem of mixed forests; regeneration and responses to disturbance; origins and history of Australian rain forest; the rain forest fauna; mangroves; and the human influence. Rainforest is currently found along the eastern seaboard, from the NE tip of Queensland south to Tasmania; there are also patches in N Northern Territory. The vegetation type was once more widespread in Australia, and its contraction reflects millennia of environmental change together with human activity. Distinctions are drawn between subtropical, dry, warm temperate and cool temperate rainforests in terms of flora and physiognomy as well as environment. Threats to Australian rain forests come from recent exploitation, especially for logging, and conservation and management issues are raised. -P.J.Jarvis
Transects across the margins of rainforests with eucalypt forests at two sites in New South Wales are described. At Girard State Forest along ten transects it was consistently found that pure rainforest occurs where there is no evidence of past burning; and that rainforest tree species appear to be invading and replacing eucalypt forest through a formerly burned ecotone area. A similar pattern was found at Barrington Tops. It is suggested that adaptations shown by species of tall open forests which enable them to regenerate rapidly after burning may have evolved initially in a fire free, prehuman rainforest environment in response to other types of disturbance.
Eidothea hardeniana (Proteaceae) is a narrow endemic representative of an ancient lineage restricted to a single site in northern New South Wales (Australia). This study aims to identify the life‐history traits most likely to have influenced the current distribution pattern of this rain forest tree.
Using ecological and molecular analyses we found that its range is limited by the absence of efficient dispersal mechanisms rather than by habitat availability, or as a result of a recent bottleneck or of reproductive failure.
Resprouts can take over the position of senesced plants, even in the absence of disturbance, allowing local persistence and the maintenance of genetic diversity. Long‐term persistence and preferential outcrossing further favour relatively high levels of diversity ( H E = 0.542) despite a small effective population size (N e = 21.6).
We used eight life‐history traits to assess if the E. hardeniana findings were valid across 258 local taxa. Current distribution patterns of rain forest species within a species‐rich community were accounted for by linking two important components of community assembly theory: dispersal and niche assembly.
The interaction of the seed‐based dispersal dimension and resprouting potential best explains the current distribution of rare local taxa. Major dimensions of life‐history trait variation were identified among local plant species, suggesting that a range of interacting traits contribute to a species’ response to environmental variables and mitigate the influence of potentially adverse circumstances.
The benefits of merging ecological and genetic approaches to interpret species distribution and population structure are applicable across a broader range of studies. Our findings highlight how currently constrained palaeo‐endemic species with small populations in refugial habitats may retain the capacity to both persist and expand in response to changing circumstances and opportunities. This has important implications for species conservation, habitat management and reserve design.
Fire has played a decisive role in Post-Glacial biological and cultural evolution in the Mediterranean Region. Its evolutionary impact on plants has been manifested by feedback responses, in which the fire and its after-effects selected plants for physiological and other mechanisms that enable direct fire tolerance or permit avoidance followed by vegetative and reproductive regeneration.
The dominant, sclerophyll, drought-tolerant phanerophytes of the maqui are obligatory rootsprouters, whereas the subordinate, drought-evading chamaephytes, as well as herbaceous perennials, are both vegetative and reproductive regenerators and are well adapted to new, fire-denuded habitats. Annual and perennial grass fire-followers are also able to escape high surface fire temperatures with the aid of torsion devices on seeds. Evolutionary strategies to overcome fire are closely interwoven with those against other environmental stresses such as drought and grazing. These combinations of stresses have brought about convergence in plant form and function in mediterranean climates.
Fire has thus been important in the evolution of more xeric grasslands and woodlands and more mesic maqui and shrubland communities. Contrary to the present view of fire as simply destructive, both fire and grazing have favored genetical as well as ecological diversity. They should be studied as integral components of Mediterranean ecosystems and their evolution.
A widely‐used description of vegetation response to fire is that species can be clearly classified as sprouters or non‐sprouters. We aimed to assess: (1) how well this dichotomous classification (sprouter/non‐sprouter) described the responses of a semi‐arid flora to experimental disturbance; (2) how similar were sprouting responses to treatments mimicking intense herbivory and fire; (3) how well easily‐measured traits could predict sprouting. Sprouting was assessed for 45 species from a range of growth forms (grasses, forbs, sub‐shrubs, woody shrubs and trees) from semi‐arid south‐eastern Australia. We used two treatments: clipping at stem base, and clipping followed by burning with a blowtorch.
A dichotomy accounted for >60% of deviance explained by species identity. Models with three or four groups were not substantially better. The dichotomy was not between 0% and 100% sprouting, rather between ‘weak’ and ‘strong’ sprouters. Probabilities of sprouting for weak sprouters were 23% after clipping and 6% after burning, while strong sprouters had sprouting probabilities of 90% after clipping and 79% after burning. While sprouting varied in space and time, the dichotomy was robust to this variation. Sprouting ability increased with size in most of the species with variable sprouting.
Sprouting was partially related to growth form; grasses sprouted strongly, chenopods weakly, and forb and woody species covered the range of sprouting. Strong sprouters were likely to have more stems per plant, greater basal area, shorter potential height and deeper buds than weak sprouters. A hierarchical model that used growth form and then stems‐per‐plant provided a simple, robust predictor of sprouting.
Four‐fifths of species responded consistently to clipping and burning while one‐fifth of species were strong sprouters after clipping but weak sprouters after burning. Burning reduced sprouting most in intermediate sprouters. Differences between sprouting after clipping and burning reflected increased intensity and were related to the depth of buds below ground.
Aim This study documents the effects of multiple fires and drought on the woody structure of a north Australian savanna never grazed by domestic stock.
Location The study was conducted in a 500 ha pocket of Eucalyptus-dominated savanna surrounded by a late Quaternary lava flow. The flow is known as the Great Basalt Wall, located c. 50 km northeast of Charters Towers in semi-arid north-eastern Australia. This region was exposed to the largest 5-year rainfall deficit on record between 1992 and 1996.
Methods All individual woody plants were tagged within a 1.56 ha plot. Species were segregated into their habitat affinities (rain forest, ecotone, savanna) and regeneration strategy (resprouter, seeder). The survivorship of plants within these categories was analysed in relation to fire intensity from the first fire, and to each of four fires lit between 1996 and 2001.
Results Before the first fire, the plot contained thirty-one tree species including twenty-one typical of the surrounding dry rain forest. These rain forest species were represented by small individuals and constituted <1% of the total basal area of woody plants. The basal area of savanna trees was 7.5 m2 ha−1 at the commencement of monitoring, although 31% had recently died and others had major crown damage. Further death of the drought debilitated savanna trees was substantial during the first year of monitoring and the basal area of live savanna trees declined to 1.1 m2 ha−1 after 5 years. Most species from both rain forest and savanna were classified as resprouters and are capable of regenerating from underground organs after fire. Species without this ability (rain forest seeders and ecotone seeders) were mostly eliminated after the first two consecutive fires. Among resprouters, survivorship declined as fire intensity increased and this was more pronounced for rain forest than for savanna species. Repeated burning produced a cumulative effect of decreasing survivorship for rain forest resprouters relative to savanna resprouters.
Main conclusions The study provides evidence that savanna and rain forest trees differ in fire susceptibility and that recurrent fire can explain the restricted distribution of rain forest in the seasonally arid Australian tropics. The time of death of the savanna trees is consistent with the regional pattern after severe drought, and highlights the importance of medium term climate cycles for the population dynamics of savanna tree species and structure of Australian savannas.
Soil phosphate and the delimitation of plant communities in eastern Australia.
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Special Climate Statement 72 -dangerous bushfire weather in spring 2019
BOM (2019) 'Special Climate Statement 72 -dangerous bushfire weather
in spring 2019.' (Bureau of Meteorology: Commonwealth of Australia)
Response of montane wet sclerophyll forest understorey species to fire: evidence from high and low intensity fires
- M L Campbell
- P J Clarke
Campbell ML, Clarke PJ (2006) Response of montane wet sclerophyll forest
understorey species to fire: evidence from high and low intensity fires.
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