Fire frequency and time‐since‐fire effects on the open‐forest and woodland flora of Girraween National Park,south‐east Queensland,Australia

Abstract The effects of recent fire frequency and time‐since‐fire on plant community composition and species abundance in open‐forest and woodland vegetation in Girraween National Park, south‐east Queensland, Australia, were examined. Cover‐abundance data were collected for shrub and vine species in at least 10 400‐m² plots in each of four study areas. Study areas were within one community type and had burnt most recently either 4 or 9 years previously. Variations in fire frequency allowed us to compare areas that had burnt at least three times in the previous 25 years with less frequently burnt areas, and also woodlands that had experienced a 28‐year interfire interval with more frequently burnt areas. Although species richness did not differ significantly with either time‐since‐fire or fire frequency, both these factors affected community composition, fire frequency being the more powerful. Moisture availability also influenced floristics. Of the 67 species found in five or more plots, six were significantly associated with time‐since‐fire, whereas 11 showed a significant difference between more and less frequently burnt plots in each of the two fire‐frequency variables. Most species, however, did not vary in cover‐abundance with the fire regime parameters examined. Even those species that showed a marked drop in cover‐abundance when exposed to a particular fire regime generally maintained some presence in the community. Five species with the capacity to resprout after fire were considered potentially at risk of local extinction under regimes of frequent fire, whereas two species were relatively uncommon in long‐unburnt areas. Variable fire regimes, which include interfire intervals of at least 15 years, could be necessary for the continuity of all species in the community.     

Fire severity influences the post-fire habitat structure and abundance of a cool climate lizard

In the spring and summer of 2019–2020, the ‘Black Summer’ bushfires burned more than 97 000 km² of predominantly Eucalyptus dominated forest habitat in eastern Australia. The Black Summer bushfires prompted great concern that many species had been imperilled by the fires. Here, we investigate the effects that fire severity had on the habitat and abundance of a cool climate lizard Eulamprus tympanum that was identified as a species of concern because 37% of its habitat was burnt in the Black Summer bushfires. We quantified habitat structure and the abundance of E. tympanum at sites which were unburnt, burnt at low severity and at high severity 10, 15 and 23 months after the fires. Our classification of fire severity based on scorch height and canopy status corresponded well with the Australian Government Google Earth Engine Burnt Area Map (AUS GEEBAM) fire severity layer. Ten months after the fires, sites burnt at high severity had less canopy cover, more bare ground and less fine fuel than sites burnt at low severity or unburnt sites. The abundance of E. tympanum varied with survey occasion and was greatest during the warmest sampling period and lowest during the coolest sampling period. The abundance of E. tympanum was consistently lower on sites burnt at high severity than sites burnt at low severity or unburnt sites. Our findings show that higher severity fires had a greater effect on E. tympanum than low severity fires. Our results suggest that E. tympanum were likely to have persisted in burnt sites, with populations in low severity and unburnt sites facilitating population recovery in areas burnt at high severity. Our results also suggest that wildfire impacts on E. tympanum populations will increase because the frequency and extent of severe fires are expected to increase due to climate change.     

Using a rainforest-flame forest mosaic to test the hypothesis that leaf and litter fuel flammability is under natural selection

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.     

Fire‐mediated niche‐separation between two sympatric small mammal species

Fire is a key ecological process influencing the population dynamics of small mammals. Whilst shifting competitive advantage amongst small mammal species following a single fire event is well‐documented, there has been little investigation of the potential influence of fire frequency on small mammal interspecific interactions. In this study, we investigated the effect of fire frequency on the abundance of two small dasyurid mammals, Antechinus stuartii and A. flavipes, which occur sympatrically in some parts of their range. The two antechinus species are known to have different habitat preferences, so it is possible that fire regimes may promote their coexistence in areas of sympatry by altering vegetation structure. To investigate this possibility, we estimated the abundance of both species using replicate sites which differed in the number of times burnt (1–4) during the last four decades, but with identical time‐since‐fire. Proportionally, we captured greater numbers of A. stuartii in less frequently burnt sites and greater numbers of A. flavipes in more‐frequently burnt sites. Hence, fire may mediate niche‐separation between these two species. To clarify further this pattern of response to fire frequency, we investigated which structural habitat variables differed between fire frequencies, and compared antechinus abundances with structural vegetation characteristics. We found a trend for lower ground cover density under higher fire frequencies. This offers one potential explanation of the patterns of abundance that we observed. Our study provided insights into the complexities of small mammal responses to fire, and strongly suggests that fire could mediate competitive interactions between species.     

Effects of repeated burning on Mediterranean communities of the northeastern Iberian Peninsula

Question: In relation to a single fire, do repeated wildfires in Mediterranean type ecosystems (1) reduce plant species richness or diversity; (2) modify patterns of abundance or dominance of plant species or (3) alter plant composition? Location: Pinus halepensis dominated communities of Catalonia, northeastern Iberian Peninsula, western Mediterranean Basin. Methods: Regional, paired design with 14 study sites, each consisting of a once burnt area (1994) and a twice burnt area (1975–1993 and 1994). Ten years after the last fire, we recorded all vascular plant species present in nested plots and quantified their relative abundances on transects. We compared species richness, diversity, dominance and relative abundance and species‐area correlations between paired once and twice burnt areas and assessed their floristic composition similarity. Results: No statistically significant differences were found in species richness or diversity. Slopes of species‐area correlations were higher in once burnt areas. In twice burnt areas, dominance by one or two species was higher. P. halepensis showed lower relative abundance and nanophanerophytes showed higher relative abundance. No differences were found for resprouter, seeder or resprouter‐seeder species. Floristic composition similarity between paired areas tended to be higher in less productive sites. Conclusions: Fire recurrence had contrasting effects on species richness at different spatial scales. Repeated burning reduced the relative abundance of the dominant tree species, which resulted in a higher relative abundance of shrubs. It also promoted the dominance of herbs, particularly Brachypodium retusum. However, it did not change the relative abundance of regenerative groups. Paired areas were more similar as they were more Mediterranean in terms of climatic conditions.     

Effects of fire on the structure and composition of open eucalypt forests

Abstract Fires are integral to the healthy functioning of most ecosystems and are often poorly understood in policy and management, however, the relationship between floristic composition and habitat structure is intrinsically linked, particularly after fire. The aim of this study was to test whether the variability of habitat structure or floristic composition and abundance in forests at a regional scale can be explained in terms of fire frequency using historical data and experimental prescribed burns. We tested this hypothesis in open eucalypt forests of Fraser Island off the east coast of Australia. Fraser Island dunes show progressive stages in plant succession as access to nutrients decreases across the Island. We found that fire frequency was not a good predictor of floristic composition or abundance across dune systems; rather, its affects were dune specific. In contrast, habitat structure was strongly influenced by fire frequency, independent of dune system. A dense understorey occurred in frequently burnt areas, whereas infrequently burnt areas had a more even distribution of plant heights. Plant communities returned to pre‐burn levels of composition and abundances within 6 months of a fire and frequently burnt areas were dominated by early successional species of plant. These ecosystems were characterized by low diversity and frequently burnt areas on the east coast were dominated by Pteridium. Greater midstorey canopy cover in low frequency areas reduces light penetration and allows other species to compete more effectively with Pteridium. Our results strongly indicate that frequent fires on the Island have resulted in a decrease in relative diversity through dominance of several species. Prescribed fire represents a powerful management tool to shape habitat structure and complexity of Fraser Island forests.     

Effects of fire on vegetation and arthropods in a coastal heath,south‐east Queensland

Fire is an important part of many Australian ecosystems, and determining how it affects different vegetation communities and associated fauna is of particular interest to land managers. Here, we report on a study that used sites established during a 39‐year fire experiment in coastal heathland in southeastern Queensland to compare arthropod abundance and vegetation in 1.5–2.6 ha sites that were (i) long unburnt, (ii) burnt every 5 years and (iii) burnt every 3 years. We found that the abundance of ants was more than four times higher in the frequently burnt sites compared to long unburnt sits. Moreover, long unburnt sites had greater dominance of Xanthorrhoea johnsonii and Caustis recurvata, whereas burnt sites had greater cover of Lomandra filiformis, Leucopogon margarodes and Leucopogon leptospermoides. Our findings show that frequent fire can alter vegetation structure and composition, and this is matched by an increase in the relative dominance of ants in the arthropod community.     

Response of plant species and life form diversity to variable fire histories and biomass in the jarrah forest of south‐west Australia

Frequent fires reduce the abundance of woody plant species and favour herbaceous species. Plant species richness also tends to increase with decreasing vegetation biomass and cover due to reduced competition for light. We assessed the influence of variable fire histories and site biomass on the following diversity measures: woody and herbaceous species richness, overall species richness and evenness, and life form evenness (i.e. the relative abundance or dominance among six herbaceous and six woody plant life forms), across 16 mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest stands in south‐west Australia. Fire frequency was defined as the total number of fires over a 30‐year period. Overall species richness and species evenness did not vary with fire frequency or biomass. However, there were more herbaceous species (particularly rushes, geophytes and herbs) where there were fewer shrubs and low biomass, suggesting that more herbaceous species coexist where dominance by shrubs is low. Frequently burnt plots also had lower number and abundance of shrub species. Life form evenness was also higher at both high fire frequency and low biomass sites. These results suggest that the impact of fire frequency and biomass on vegetation composition is mediated by local interactions among different life forms rather than among individual species. Our results demonstrate that measuring the variation in the relative diversity of different woody and herbaceous life forms is crucial to understanding the compositional response of forests and other structurally complex vegetation communities to changes in disturbance regime such as increased fire frequency.     

Variation in the impact of exotic grasses on native plant composition in relation to fire across an elevation gradient in Hawaii

The impact that an exotic species can have on the composition of the community it enters is a function of its abundance, its particular species traits and characteristics of the recipient community. In this study we examined species composition in 14 sites burned in fires fuelled by non‐indigenous C4 grasses in Hawaii Volcanoes National Park, Hawaii. We considered fire intensity, time since fire, climatic zone of site, unburned grass cover, unburned native cover and identity of the most abundant exotic grass in the adjacent unburned site as potential predictor variables of the impact of fire upon native species. We found that climatic zone was the single best variable for explaining variation in native cover among burned sites and between burned and unburned pairs. Fire in the eastern coastal lowlands had a very small effect on native plant cover and often stimulated native species regeneration, whereas fire in the seasonal submontane zone consistently caused a decline in native species cover and almost no species were fire tolerant. The dominant shrub, Styphelia tameiameia, in particular was fire intolerant. The number of years since fire, fire intensity and native cover in reference sites were not significantly correlated with native species cover in burned sites. The particular species of grass that carried the fire did however, have a significant effect on native species recovery. Where the African grass Melinis minutiflora was a dominant or codominant species, fire impacts were more severe than where it was absent regardless of climate zone. Overall, the impacts of exotic grass‐fuelled fires on native species composition and cover in seasonally dry Hawaiian ecosystems was context specific. This specificity is best explained by differences between the climatic zones in which fire occurred. Elevation was the main physical variable that differed among the climatic zones and it alone could explain a large percentage of the variation in native cover among sites. Rainfall, by contrast, did not vary systematically with elevation. Elevation is associated with differences in composition of the native species assemblages. In the coastal lowlands, the native grass Heteropogon contortus, was largely responsible for positive changes in native cover after fire although other native species also increased. Like the exotic grasses, this species is a perennial C4 grass. It is lacking in the submontane zone and there are no comparable native species there and almost all native species in the submontane zone were reduced by fire. The lack of fire tolerant species in the submontane zone thus clearly contributes to the devastating impact of fire upon native cover there.     

The effect of fire interval on post‐fire understorey communities in Yellowstone National Park

Questions: How does the time interval between subsequent stand‐replacing fire events affect post‐fire understorey cover and composition following the recent event? How important is fire interval relative to broad‐ or local‐scale environmental variability in structuring post‐fire understorey communities? Location: Subalpine plateaus of Yellowstone National Park (USA) that burned in 1988. Methods: In 2000, we sampled understorey cover and Pinus contorta density in pairs of 12–yr old stands at 25 locations. In each pair, the previous fire interval was either short (7–100 yr) or long (100–395 yr). We analysed variation in understorey species richness, total cover, and cover of functional groups both between site pairs (using paired t‐tests) and across sites that experienced the short fire intervals (using regression and ordination). We regressed three principal components to assess the relative importance of disturbance and broad or local environmental variability on post‐fire understorey cover and richness. Results: Between paired plots, annuals were less abundant and fire‐intolerant species (mostly slow‐growing shrubs) were more abundant following long intervals between prior fires. However, mean total cover and richness did not vary between paired interval classes. Across a gradient of fire intervals ranging from 7–100 yr, total cover, species richness, and the cover of annuals and nitrogen‐fixing species all declined while the abundance of shrubs and fire‐intolerant species increased. The few exotics showed no response to fire interval. Across all sites, broad‐scale variability related to elevation influenced total cover and richness more than fire interval. Conclusions: Significant variation in fire intervals had only minor effects on post‐fire understorey communities following the 1988 fires in Yellowstone National Park.     

Remotely‐sensed foliage cover and ground‐measured stand attributes are complimentary when estimating tree hollow abundances across relictual woodlands in agricultural landscapes

Hollows, also known as tree cavities, are critical to the survival of many animal species but are too poorly mapped across landscapes to allow for their adequate consideration in regional planning. Managing cost is important, so we tested whether freely available satellite‐derived foliage projective cover and field‐measured stand attributes could be used separately or combined to predict tree hollow abundance in relictual Australian temperate woodlands. Satellite‐derived foliage projective cover revealed variation in woody vegetation densities both within mapped woodland remnants and cleared areas of the agricultural matrix. Plot‐based field assessment of the actual number of hollows in each one‐hectare site (n = 110 sites) revealed a relationship with foliage cover. Improvement of the model was achieved if site‐based estimates of the proportion of the canopy due to Eucalyptus species and the number of mature trees per hectare were included. Remotely sensed foliage cover can improve on traditional vegetation mapping for predicting hollow‐bearing tree and hollow abundances at landscape scales when managing hollow‐dependent fauna habitat across relictual woodlands in temperate Australian agricultural landscapes. At finer scales, the addition of other predictors is necessary to raise the accuracy of the predicted hollow densities.     

Soil arthropoda of post-fire successions in northern taiga of West Siberia

The soil arthropoda population of northern taiga was investigated in the primary pine forest which had not been subject to any fire for at least 100 years and at two burnt sites of different opost-fire successions. The population of the primary nonburnt forest is represented by 54 microarthropoda species. The mesofauna is composed almost exceptionally of spiders: 10 species of them were identified. The foliage underwood develops on young burnt sites; the soil is covered with thick mossy cushions, with spots of reedgrass. The density of collembolan and oribatid mite population there is about two times lower than in nonburnt pine forests; gamasid mites are absent. The microarthropoda population is represented by the species which are common in the surrounding primary pine forests. The mesofauna consists mainly of ground beetles, open-land predators, and myxophytophagans. Spiders are represented by some widespread mobile species of low density. A mixed forest with mossy-lichen cover is formed on old burnt sites (of an age of about 50 years). Diversity and density of microarthropoda increase reaching the values characteristic of the primary forest; however, the species composition and dominance are still different. The fraction of spiders in mesofauna increases. The ground beetle population is the most abundant and diverse.     

Rapid Recovery of an Urban Remnant Reptile Community following Summer Wildfire

Reptiles in urban remnants are threatened with extinction by increased fire frequency, habitat fragmentation caused by urban development, and competition and predation from exotic species. Understanding how urban reptiles respond to and recover from such disturbances is key to their conservation. We monitored the recovery of an urban reptile community for five years following a summer wildfire at Kings Park in Perth, Western Australia, using pitfall trapping at five burnt and five unburnt sites. The reptile community recovered rapidly following the fire. Unburnt sites initially had higher species richness and total abundance, but burnt sites rapidly converged, recording a similar total abundance to unburnt areas within two years, and a similar richness within three years. The leaf-litter inhabiting skink Hemiergis quadrilineata was strongly associated with longer unburnt sites and may be responding to the loss of leaf litter following the fire. Six rarely-captured species were also strongly associated with unburnt areas and were rarely or never recorded at burnt sites, whereas two other rarely-captured species were associated with burnt sites. We also found that one lizard species, Ctenotus fallens, had a smaller average body length in burnt sites compared to unburnt sites for four out of the five years of monitoring. Our study indicates that fire management that homogenises large areas of habitat through frequent burning may threaten some species due to their preference for longer unburnt habitat. Careful management of fire may be needed to maximise habitat suitability within the urban landscape.     

The effect of fire history in shaping diversity patterns of flower-visiting insects in post-fire Mediterranean pine forests

Fire affects diversity and structure of flower-visitor communities. We explored the effect of fire history on the diversity patterns and structure of the flower-visitor guilds (bees, beetles, flies, sawflies, and wasps), across a post-fire regeneration sequence of pine forests in Rhodes Island, Greece. Fire history was defined by fire frequency and post-fire age of sites. We did not find significant differences in species richness and abundance per guild between fire-history regimes except for the abundance of flies, sawflies and the entire flower-visitor community. Fire strongly affected the community structure of bees, beetles, and sawflies. Some of the most abundant and common species responded significantly to fire in terms of abundance; yet, we observed no significant variation in the abundance of the common species of bees, the most prominent pollinator group, implying that provision of pollination services may not be considerably affected by fire. Long-unburnt sites displayed higher heterogeneity in species composition compared to recently-burnt sites (either burnt once or twice). This pattern deviated significantly from null expectations when analyzing the abundance-based metric of β-diversity and was obscure in the case of the presence/absence-based metric, indicating that fire affected mainly the spatial distribution of individuals, i.e. the main change is not due to species turnover but to changes in relative abundance. Furthermore, the species composition in recently-burnt sites (burnt once in 2008) were more similar than in twice-burnt sites (including areas burnt once between 1984 and 1992, and in 2008), indicating that fire frequency affected post-fire heterogeneity of species composition.     

Effects of spring and autumn fires on the composition of Chionochloa rigida tussock grassland,New Zealand

Two areas of Chionochloa rigida tussock grassland on Flagstaff Hill were burnt in autumn and spring 1976, respectively. Plant species cover and frequency were recorded in 1977 and 1985. Initially, plant cover and frequency were lower, and the area of bare ground was greater, on the autumn burnt site. After nine years, cover and frequency values were similar for most species, and bare ground was rare, on both sites. Over this period, recovery in size of indigenous tussock-forming physiognomic dominants resulted in suppression of intertussock sub-shrubs, herbs and grasses that were initially favoured by reduction of competition after fire. Plant species most tolerant of fire have features that protect the meristem, for instance an underground perennating organ or dense tillering.     

Post‐fire recovery of revegetated woodland communities in south‐eastern Australia

The primary goal of restoration is to create self‐sustaining ecological communities that are resilient to periodic disturbance. Currently, little is known about how restored communities respond to disturbance events such as fire and how this response compares to remnant vegetation. Following the 2003 fires in south‐eastern Australia we examined the post‐fire response of revegetation plantings and compared this to remnant vegetation. Ten burnt and 10 unburnt (control) sites were assessed for each of three types of vegetation (direct seeding revegetation, revegetation using nursery seedlings (tubestock) and remnant woodland). Sixty sampling sites were surveyed 6 months after fire to quantify the initial survival of mid‐ and overstorey plant species in each type of vegetation. Three and 5 years after fire all sites were resurveyed to assess vegetation structure, species diversity and vigour, as well as indicators of soil function. Overall, revegetation showed high (>60%) post‐fire survival, but this varied among species depending on regeneration strategy (obligate seeder or resprouter). The native ground cover, mid‐ and overstorey in both types of plantings showed rapid recovery of vegetation structure and cover within 3 years of fire. This recovery was similar to the burnt remnant woodlands. Non‐native (exotic) ground cover initially increased after fire, but was no different in burnt and unburnt sites 5 years after fire. Fire had no effect on species richness, but burnt direct seeding sites had reduced species diversity (Simpson's Diversity Index) while diversity was higher in burnt remnant woodlands. Indices of soil function in all types of vegetation had recovered to levels found in unburnt sites 5 years after fire. These results indicate that even young revegetation (stands <10 years old) showed substantial recovery from disturbance by fire. This suggests that revegetation can provide an important basis for restoring woodland communities in the fire‐prone Australian environment.     

Effects of fire on sward structure and grazing in western Serengeti, Tanzania

In Serengeti fire is used as a management tool to improve the forage quality for large herbivores. However, little is known of the effects of fire on grazing resources particularly sward structure, its influence on herbivore forage patch selection and utilization to the relative amount of phytomass consumed in burnt and nonburnt patches. From September 2003 to July 2004, consumption of phytomass by large herbivores was assessed with eight samplings in six grassland sites in the Western Corridor in Serengeti National Park. Each site had burnt and nonburnt plots. Movable cages were used to exclude grazing between samplings and plant material harvests were used to assess phytomass and sward structure changes in time. Nonburnt grasslands had consistently larger phytomass at all sampling events whereas the ratio for live leaf/total phytomass was higher in burnt grassland at early postfire stages, but declined later in the season. Moreover, periodic consumption of both total phytomass and different phytomass components shifted between burnt and nonburnt grasslands, but there were also large site-specific responses. The shift appears to be related to the balance between the amount of phytomass available and the quality of the forage in terms of the ratio between live and total phytomass. The study highlights the significance of maintaining mosaics of burnt and nonburnt areas with an adequate provision of forage amount and quality all year round.     

Influence of fire and soil nutrients on native and non-native annuals at remnant vegetation edges in the Western Australian wheatbelt

Abstract. The effect of fire on annual plants was examined in two vegetation types at remnant vegetation edges in the Western Australian wheatbelt. Density and cover of non-native species were consistently greatest at the reserve edges, decreasing rapidly with increasing distance from reserve edge. Numbers of native species showed little effect of distance from reserve edge. Fire had no apparent effect on abundance of non-natives in Allocasuarina shrubland but abundance of native plants increased. Density of both non-native and native plants in Acacia acuminata-Eucalyptus loxophleba woodland decreased after fire. Fewer non-native species were found in the shrubland than in the woodland in both unburnt and burnt areas, this difference being smallest between burnt areas. Levels of soil phosphorus and nitrate were higher in burnt areas of both communities and ammonium also increased in the shrubland. Levels of soil phosphorus and nitrate were higher at the reserve edge in the unburnt shrubland, but not in the woodland. There was a strong correlation between soil phosphorus levels and abundance of non-native species in the unburnt shrubland, but not after fire or in the woodland. Removal of non-native plants in the burnt shrubland had a strong positive effect on total abundance of native plants, apparently due to increases in growth of smaller, suppressed native plants in response to decreased competition. Two native species showed increased seed production in plots where non-native plants had been removed. There was a general indication that, in the short term, fire does not necessarily increase invasion of these communities by non-native species and could, therefore be a useful management tool in remnant vegetation, providing other disturbances are minimised.     

Is leaf-level photosynthesis related to plant success in a highly productive grassland?

We addressed the question: “Are short-term, leaf-level measurements of photosynthesis correlated with long-term patterns of plant success?” in a productive grassland where interspecific competitive interactions are important. To answer this question, seasonal patterns of leaf-level photosynthesis were measured in 27 tallgrass prairie species growing in sites that differed in species composition and productivity due to differences in fire history. Our specific goals were to assess the relationship between gas exchange under field conditions and success (defined as aerial plant cover) for a wide range of species, as well as for these species grouped as dominant and sub-dominant grasses, forbs, and woody plants. Because fire increases productivity and dominance by grasses in this system, we hypothesized that any relationship between photosynthesis and success would be strongest in annually burned sites. We also predicted that regardless of fire history, the dominant species (primarily C₄ grasses) would have higher photosynthetic rates than the less successful species (primarily C₃ grasses, forbs and woody plants). Because forbs and woody species are less abundant in annually burned sites, we expected that these species would have lower photosynthetic rates in annually burned than in infrequently burned sites. As expected, the dominant C₄?grasses had the highest cover on all sites, relative to?other growth forms, and they had the highest maximum and seasonally averaged photosynthetic rates (17.6 ± 0.42 μmol m^?2 s^?1). Woody species had the lowest average cover as well as the lowest average photosynthetic rates, with subdominant grasses and forbs intermediate in both cover and photosynthesis. Also as predicted, the highest overall photosynthetic rates were found on the most productive annually burned site. Perhaps most importantly, a positive relationship was found between leaf-level photosynthesis and cover for a core group of species when data were combined across all sites. These data support the hypothesis that higher instantaneous rates of leaf-level photosynthesis are indicative of long-term plant success in this grassland. However, in contrast to our predictions, the subdominant grasses, forbs and woody species on the annually burned site had higher photosynthetic rates than in the less frequently burned sites, even though their average cover was lower on annually burned sites, and hence they were less successful. The direct negative effect of fire on plant cover and species-specific differences in the availability of resources may explain why photosynthesis was high but cover was low in some growth forms in annually burned sites.     

Estimating population abundance in plant species with dormant life-stages: Fire and the endangered plant Grevillea caleyi R. Br.

Summary Assessment of the conservation significance of a species at a particular site involves estimating the population size. Generally this is based on a single survey. However, where plant species vary greatly in abundance in response to disturbance regimes, there will be uncertainty associated with the use of single estimates of abundance. The interpretation of such estimates is dependent on an understanding of the ecology of the species and the disturbance regimes that impact on it. We examined the usefulness of abundance estimates in the endangered shrub Grevillea caleyi (a fire‐sensitive shrub with a persistent soil seed bank) from south‐eastern Australia, where fire is a major landscape disturbance. Comparisons of estimates of abundance before and after fire showed very large changes in the number of plants of G. caleyi above ground. Changes in abundance of over two orders of magnitude were observed. The longer the site was left unburnt, the greater the magnitude of change in abundance after the next fire. Above‐ground plants may be rare or absent at sites unburnt for over 15–20 years, but were abundant after fire, due to re‐establishment from the soil seed bank. Sites burnt by two fires in quick succession showed declines in population abundance, most likely due to the soil seed bank not being replenished between such short interval fires. Assessments of the conservation significance of remnant sites of G. caleyi and similar species based on a single sample of above‐ground plant abundance at one time are considered inappropriate. The amount of available habitat for G. caleyi, either as area of occupancy or preferably extent of available habitat, was a moderate predictor of the likely magnitude of abundance in the species after fire. However, the usefulness of these measures for species whose biology is comparable to Grevillea caleyi, will be limited due to factors relating to the degree of species‐specific habitat requirements, local site fire history and the impact of any one fire on resultant post‐fire germination levels. Any assessment of conservation significance will require the interpretation of available information in relation to the ecology of a species.