Mohammed A. A. Alshehri a,b , Stephen P. Bonser a , Adrian G. Fisher c

a Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences,
UNSW Sydney, Sydney 2052, Australia.
b The Institute of Environmental Protection Technology (IEPT), King Abdulaziz City for Science and
Technology (KACST), Riyadh 11442, Saudi Arabia.
C Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental
Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
*Corresponding Author: Stephen Patrick Bonser s.bonser@unsw.edu.au

Fire can have significant impacts on community assembly. In addition, fires are increasingly impacting ecosystems with no recent history of fire impacts. We examined the impact of fires on community diversity and composition in previously unburned alpine plant communities. We studied three study sites along the Asir Mountains highlands, in Southwestern of Saudi Arabia. These communities have no recorded history of fire disturbances. We tested the following predictions: 1) Fire will decrease species diversity, particularly in ecosystems with no prior history of fire, as few species are likely to respond and adapt to such disturbances; 2) Fire will increase local extinctions of species susceptible to disturbance. We conducted our fieldwork four years after the last wildfire. We established 20 plots (20x20 m2) in burned and unburned communities in each of three ecosystems (120 plots in total) that had experienced fire in the last 4 years. We measured the number of species (richness), their identity, and species abundance. We found that species richness was significantly lower in burnt plots compared to unburned plots (p < 0.001). We also found that fire significantly reduced species abundance: burnt plots had lower total abundance than unburnt plots (< 0.001). Fire disturbances significantly impact plant communities and composition by reducing plant species richness and abundance. Fire can significantly increase the risk of local extinctions among species most sensitive to disturbance. Our results suggest that fire will significantly alter the assembly of communities with no previous fire history.

Fire season in fire-frequent Australian tropical savanna has been shown to impact soil microbial abundance. How does community structure and composition respond? A previously opaque system of fundamental interactions between fire, flora and edaphic soil communities was explored through a combination of field and molecular methodologies. Using a large-scale fire experiment in Australia, near Darwin, Northern Territory, we focused on plots that had not been burned in > 30 years, and plots burned every two years in the early dry season (June) and late dry season (October). Using amplicon sequencing to measure the impact of fire regimes and litter type (broadleaf, grass) on microbial diversity, we examined the influence of fire regime mediated through plant community shifts defined by litter type. Community structure (alpha diversity, richness, evenness) of both bacteria and fungi was relatively stable between early and late burning fire regimes, with changes observed for bacteria more so than fungi. However, frequent fire, regardless of season, impacted composition (Bray-Curtis) when compared to unburnt treatments. Overall, soil and litter microbial community responses in this study were weaker than those demonstrated in rarely burned ecosystems but supported the literature indicating that legacies of frequent fire foster fire-resilient taxa.

Fire is a key ecological process in many tropical ecosystems, yet its role in shaping ground-layer plant diversity remains underappreciated in both conservation and management planning. In this talk, I present insights from two ecosystems shaped by fire: the open grassy landscapes of Madagascar and the Miombo woodlands of Zambia. In Madagascar, orchids, which are typically associated with humid rainforests, are shown to occur extensively in open ecosystems, with 31% of species found there and 17% restricted to them. These species flower synchronously after the fire season, starting from the onset of the wet season, and many exhibit traits associated with fire adaptation. They are concentrated in high-elevation grasslands, scrubs, and rocky outcrops, where seasonal fire and rainfall patterns structure plant phenology. In Zambia, a 63-year fire experiment reveals that fire-maintained Miombo savanna woodlands support greater ground-layer plant richness than fire exclusion plots. Richness is highest during the wet-to-early-dry season, and functional groups such as C₄ grasses and geoxyles are the richest in the treatments burned in the late dry season. Together, these findings highlight the importance of fire in maintaining plant diversity across contrasting ecosystems and underscore the need to integrate fire into conservation policy – not only as a disturbance to mitigate, but as a natural driver of biodiversity in fire-adapted landscapes.

Fire has long played a role in the formation and variation of Australia’s natural systems, however long-established fire regimes have been disrupted since European colonisation. In Victoria, bushfire risk to public land is managed through a series of smaller scale planned burns with a primary objective of protecting human lives and assets. Planned burns are undertaken in the window between autumn and spring, when conditions are more stable and vegetation moisture content is higher. Under a changing climate we are seeing drier winters and less predictable weather patterns, posing a potential shift in optimal burning windows.
We investigated the germination response of fire-adapted vegetation to burns undertaken in both autumn and spring 2022, within a coastal Heathy Woodland. We also investigated the effect of burn extent (totally burnt, totally unburnt, patchily burnt). We analysed plant recruitment in 720 1x1m seedling abundance surveys, and vegetation community composition in 72 10x10m surveys.
We found higher levels of recruitment with greater burn extents following autumn burns, but no influence of burn extent following spring burns. We also observed greater mortality of taxa recruiting from seed following spring burns, likely due to drier than average conditions in the subsequent summer and autumn. The open space following mortality allowed for an influx of colonising plant taxa (mostly members of Poaceae and Cyperaceae families) and invasive species.
This research of one burn year shows a potential shift in the planned burning window and highlights the need for complementary research to better understand the impacts of altered fire regimes at both a species and community level.

Large tracts of montane forests in the Australian Alps are dominated by fire-killed stands of Eucalyptus delegatensis R.T. Baker subsp. delegatensis (Alpine Ash). Alpine Ash is vulnerable to local extinction if two fires occur before an adequate canopy seed bank has developed. A significant proportion of Alpine Ash stands in NSW were burnt in 2003 and in 2020, with some stands burnt at high severity in both fire events. We present results to date of monitoring undertaken in Kosciusko National Park in 2021 and 2025 using monitoring plots established between 2008 and 2013. The focus of our monitoring is seedling recruitment in stands burnt either at low severity in 2003 and high severity in 2020, or else burnt at high severity in both 2003 and 2020. Those stands burnt twice at high severity in less than 20 years are at a particularly vulnerable stage. In 2021, we found a highly significant tendency for larger numbers of seedlings on plots burnt at low severity in 2003 and high severity in 2020 compared to plots which burnt at high severity in both 2003 and 2020. Nonetheless, there was adequate recruitment in all plots in both treatments for the re-establishment of Alpine Ash stands. In 2025 we re-counted recruits in the plots surveyed in 2021 and also measured growth rates and bud and fruit formation. Although the differential in numbers remains between the treatments, growth rates are similar. Six years post-fire, bud initiation and fruit formation has begun, but rates are currently low. A key objective of our monitoring is to document the progressive increase in the proportion of recruits in post-fire stands flowering and fruiting over the first 15 years post-fire, so that we can obtain a more precise understanding of the minimum inter-fire interval at which Alpine Ash can persist.

Grasses significantly influence bushfire behaviour in fire-prone landscapes, yet their flammability under changing climate and fire regimes remains poorly understood in temperate Australia. This study examined the flammability of two native perennial grasses (P.labillardierei, T. triandra) under combinations of two fire intensities (low and high), and two dryness levels (well-watered and dry) under controlled laboratory conditions. Four
components of flammability were quantitatively measured: ignitability (ignition probability, time to flaming ignition), combustibility (flame height), sustainability (flame duration), and consumability (percentage of material consumed). Dryness significantly influenced flammability (decreased time to flaming ignition, increased ignition probability, flame height, and percentage consumed; p<0.001) across both fire intensities and species, although it did not significantly influence flame duration (p>0.05). Flammability components, except ignition probability and time to flaming ignition, were also significantly increased by high versus low fire intensity (p<0.001). In addition, P. labillardierei was more flammable than T.triandra for all components (p<0.001), except flame height. There were very few interactive effects among dryness, fire intensity, and species, except for significant two-way interactions for biomass consumption, with stronger effects of dryness and fire intensity for P.
labillardierei than T. triandra and of fire intensity for well-watered than dry grasses (p<0.001). These findings suggest that increased fuel dryness and high fire intensity can elevate multiple components of the flammability of widespread native perennial grasses, increasing the risk of intense fires under climate scenarios characterised by increasing dryness.

Fire regimes are intensifying and shifting from historic patterns, yet the impact of wildfire on insectivorous bat species remains poorly understood. Four years after the 2019/20 Australian Black Summer Bushfires and subsequent above-average rainfall, we examined activity responses of five insectivorous bat species (as foraging guild-representatives) to habitat structure and prey availability under varying levels of fire severity and frequency, within the Greater Blue Mountains World Heritage Area. We hypothesized that, with high post-fire rainfall driving rapid vegetation regrowth, bat activity would respond to habitat structure regardless of fire treatment, while prey availability would have no significant effect across fire treatments.

We found no significant effect of wildfire on bat activity in relation to habitat structure, consistent across species. Whilst there was variation in the specific structural vegetation variables driving activity, most open- and edge-space foragers (Austronomus australis, Vespadelus vulturnus, Chalinolobus gouldii), showed a positive response to a reduction of vegetation clutter as aligned with the Optimal Foraging Theory. Activity of clutter forager Rhinolophus megaphyllus could not be explained by structural measures and may be better explained by roost proximity.

We found a lasting fire legacy effect on bat activity, with significant interactions between fire treatment, prey abundance and bat activity. Notedly, a negative association between bat activity and prey abundance was observed often at sites of high past wildfire frequency.

Our study suggests that increasing fire frequency may limit bat foraging by promoting denser vegetation regrowth, which may reduce prey accessibility and weaken top-down control on insect populations. We therefore caution against complacency for bat resilience to wildfire even within the context of fire-prone ecosystems. Given the projected increase in wildfire prevalence, long-term studies comparing recovery responses under varying climatic conditions are needed to better guide wildfire management for bat conservation.