Modeling variability in the fire response of an endangered bird to improve fire-management

The impact of plant-derived fire management prescriptions on fire-responsive bird species

In fire-prone regions, the occurrence of some faunal species is contingent on the presence of resources that arise through post-fire plant succession. Through planned burning, managers can alter resource availability and aim to provide the conditions required to promote biodiversity. Understanding how species occurrence changes at different spatial and temporal scales after fire is essential to achieve this goal. However, many fire prescriptions are guided primarily by the responses of fire-sensitive plants when setting tolerable fire intervals. This approach assumes that maintaining floristic diversity will satisfy the requirements of fauna. We surveyed bird species in two semi-arid vegetation types across an environmental gradient in south-eastern Australia. We conducted four surveys at each of 253 sites across a 75-year chronosequence of time since fire and used generalized additive mixed models to examine changes in the occurrence of birds in response to time since fire. Model predictions were compared to plant-derived fire prescriptions currently guiding fire management in the region. Time since fire was a significant predictor for 18 of 28 species modeled, in at least one vegetation type, over a gradient of 1.3° of latitude. We detected considerable variation in the responses of some species, both between vegetation types and geographically within a vegetation type. Our evaluation of plant-derived fire prescriptions suggests that the intervals considered acceptable for maintaining floristic diversity may not be sustainable for populations of birds requiring longer unburnt vegetation, with 6 of the 12 species assessed attaining a mean occurrence probability of 20.3% by the minimum tolerable fire interval, and 57.3% by the maximum tolerable fire interval, in their respective vegetation types. Our findings highlight the potential vulnerability of fire-responsive bird species if fire prescriptions are applied in a manner that fails to account for the slow development of habitat resources needed by some species, and the variation detected within the responses of species. This highlights the need for species-specific data collected at an appropriate spatial scale to inform management plans.

Fire and Its Interactions With Other Drivers Shape a Distinctive, Semi-Arid ‘Mallee’ Ecosystem

Fire shapes ecosystems globally, including semi-arid ecosystems. In Australia, semi-arid ‘mallee’ ecosystems occur primarily across the southern part of the continent, forming an interface between the arid interior and temperate south. Mallee vegetation is characterized by short, multi-stemmed eucalypts that grow from a basal lignotuber. Fire shapes the structure and functioning of mallee ecosystems. Using the Murray Mallee region in south-eastern Australia as a case study, we examine the characteristics and role of fire, the consequences for biota, and the interaction of fire with other drivers. Wildfires in mallee ecosystems typically are large (1000s ha), burn with high severity, commonly cause top-kill of eucalypts, and create coarse-grained mosaics at a regional scale. Wildfires can occur in late spring and summer in both dry and wet years. Recovery of plant and animal communities is predictable and slow, with regeneration of eucalypts and many habitat components extending over decades. Time since the last fire strongly influences the distribution and abundance of many species and the structure of plant and animal communities. Animal species display a discrete set of generalized responses to time since fire. Systematic field studies and modeling are beginning to reveal how spatial variation in fire regimes (‘pyrodiversity’) at different scales shapes biodiversity. Pyrodiversity includes variation in the extent of post-fire habitats, the diversity of post-fire age-classes and their configuration. At regional scales, a desirable mix of fire histories for biodiversity conservation includes a combination of early, mid and late post-fire age-classes, weighted toward later seral stages that provide critical habitat for threatened species. Biodiversity is also influenced by interactions between fire and other drivers, including land clearing, rainfall, herbivory and predation. Extensive clearing for agriculture has altered the nature and impact of fire, and facilitated invasion by pest species that modify fuels, fire regimes and post-fire recovery. Given the natural and anthropogenic drivers of fire and the consequences of their interactions, we highlight opportunities for conserving mallee ecosystems. These include learning from and fostering Indigenous knowledge of fire, implementing actions that consider synergies between fire and other processes, and strategic monitoring of fire, biodiversity and other drivers to guide place-based, adaptive management under climate change.

Can flexible timing of harvest for translocation reduce the impact on fluctuating source populations?

Abstract ContextSpecies translocations are used in conservation globally. Although harvest for translocation may have negative impacts on source populations, translocation programs rarely explore ways of minimising those impacts. In fluctuating source populations, harvest timing may affect its impact because population size and trajectory vary among years. AimsWe explored whether the timing and scale of harvest can be altered to reduce its impact on a fluctuating source population of Mallee Emu-wrens, Stipiturus mallee; an endangered passerine in south-eastern Australia. Mallee Emu-wren populations fluctuate with ~5–10-year drought–rain cycles. MethodsWe used population viability analysis (PVA) to compare the impact of five harvest scales (no harvest, 100, 200, 300 or 500 individuals) under three population trajectories (increasing, stable or decreasing) and two initial population sizes (our model-based estimate of the population size and the lower 95% confidence interval of that estimate). To generate a model-based estimate of the population size, we surveyed 540 sites (9ha), stratified according to environmental variables known to affect Mallee Emu-wren occurrence. We used an information-theoretic approach with N-mixture models to estimate Mallee Emu-wren density, and extrapolated results over all potential habitat. Key ResultsWe estimate that in spring 2019, the source population consisted of 6449 individuals, with a minimum of 1923 individuals (lower 95% confidence interval). Of 48 harvest scenarios, only seven showed no impact of harvest within 5 years (15%). Those seven all had increasing population trajectories and carrying capacity set to equal initial population size. Twenty-six populations showed no impact of harvest within 25 years (54%). These were either increasing populations that had reached carrying capacity or decreasing populations nearing extinction. ConclusionsInitial population size, carrying capacity, harvest scale and population trajectory were all determinants of harvest impact. Given the importance of carrying capacity, further research is required to determine its role in the Mallee Emu-wren source population. ImplicationsHarvesting Mallee Emu-wrens after high-rainfall years will have the least impact because source populations are likely to be large with increasing trajectories. For fluctuating source populations, flexibility in the timing of harvest can reduce its impact and should be considered during translocation planning.