Prescribed burning protects endangered tropical heathlands of the Arnhem Plateau, northern Australia

Population collapse of a Gondwanan conifer follows the loss of Indigenous fire regimes in a northern Australian savanna

Colonialism has disrupted Indigenous socioecological systems around the globe, including those supported by intentional landscape burning. Because most disruptions happened centuries ago, our understanding of Indigenous fire management is largely inferential and open to debate. Here, we investigate the ecological consequences of the loss of traditional Aboriginal fire management on fire-exposed savannas on the Arnhem Plateau, northern Australia, using the fire-sensitive conifer Callitris intratropica as a bio-indicator. We contrast Kakadu National Park, where traditional Aboriginal fire management was severely disrupted during the early twentieth century following Aboriginal relocation to surrounding settlements, and an adjacent Aboriginal estate where traditional Aboriginal fire management endures. Since 2006, traditional Aboriginal fire management at this site has been overlaid by a program of broad-scale institutionalized burning in the early dry season, designed to reduce greenhouse emissions. Using remote sensing, field survey, and dendrochronology, we show that on the Aboriginal estate, C. intratropica populations depend on the creation of a shifting patch mosaic of long unburned areas necessary for the recruitment of C. intratropica. However, the imposition of broad-scale fire management is disrupting this population patch dynamic. In Kakadu, there have been extreme declines of C. intratropica associated with widespread fires since the mid twentieth century and consequent proliferation of grass fuels. Fire management in Kakadu since 2007, designed to increase the size and abundance of patches of unburned vegetation, has not been able to reverse the population collapse of C. intratropica. Our study demonstrates that colonial processes including relocation of Indigenous people and institutional fire management can have deleterious consequences that are nearly irreversible because of hysteresis in C. intratropica population dynamics.

Transforming fire management in northern Australia through successful implementation of savanna burning emissions reductions projects

Savannas are the most fire-prone of Earth's biomes and currently account for most global burned area and associated carbon emissions. In Australia, over recent decades substantial development of savanna burning emissions accounting methods has been undertaken to incentivise more conservative savanna fire management and reduce the extent and severity of late dry season wildfires. Since inception of Australia's formal regulated savanna burning market in 2012, today 25% of the 1.2M km² fire-prone northern savanna region is managed under such arrangements. Although savanna burning projects generate significant emissions reductions and associated financial benefits especially for Indigenous landowners, various biodiversity conservation considerations, including fine-scale management requirements for conservation of fire-vulnerable taxa, remain contentious. For the entire savanna burning region, here we compare outcomes achieved at 'with-project' vs 'non-project' sites over the period 2000-19, with respect to explicit ecologically defined fire regime metrics, and assembled fire history and spatial mapping coverages. We find that there has been little significant fire regime change at non-project sites, whereas, at with-project sites under all land uses, from 2013 there has been significant reduction in late season wildfire, increase in prescribed early season mitigation burning and patchiness metrics, and seasonally variable changes in extent of unburnt (>2, >5 years) habitat. Despite these achievements, it is acknowledged that savanna burning projects do not provide a fire management panacea for a variety of key regional conservation, production, and cultural management issues. Rather, savanna burning projects can provide an effective operational funded framework to assist with delivering various landscape-scale management objectives. With these caveats in mind, significant potential exists for implementing incentivised fire management approaches in other fire-prone international savanna settings.

Tree hollow densities reduced by frequent late dry-season wildfires in threatened Gouldian finch (Erythrura gouldiae) breeding habitat

Abstract Context. Tree hollows are a key habitat resource for hollow-nesting species, including the northern Australian Gouldian finch (Erythrura gouldiae). Certain fire and disturbance regimes limit tree hollow availability in the northern Australian savannas. Aims. This study investigated the influence of fire regime and vegetation structure on the density of tree hollows at Gouldian finch breeding sites. Methods. Fire scars were mapped across breeding sites by using LANDSAT images. Vegetation plots within sites were spatially stratified according to three fire-regime attributes, namely, fire frequency, late dry-season wildfire frequency and time since the last fire. Tree hollow and vegetation structural attributes were measured at each vegetation plot. We modelled the relationship among hollow density, fire and vegetation attributes by using general linear mixed models with site as the random factor. Key results. We found that the highest tree-hollow density was found at plots with high eucalypt tree density and cover and with the lowest frequency of late dry-season wildfires (<1 wildfire over 5 years). Tree-hollow density declined after >2 years without fire. Hollow density was not directly related to total fire frequency. Conclusions. This study adds to previous work on grass seed resources in highlighting the importance of fire in Gouldian finch ecology. This study particularly highlighted the importance of reducing the impacts of high-intensity late dry-season wildfires because of their negative impacts on tree-hollow density, which is a key resource for breeding Gouldian finches. Implications. We recommend the use of a network of interconnected annual patchy early dry-season prescribed burns for protecting Gouldian breeding habitat from threat of high-intensity wildfires. We do NOT recommend fire exclusion from Gouldian finch breeding habitats. This is because fire risks to hollow-bearing trees, and grass seed resources, increase with the long-term accumulation of savanna litter fuels in the absence of fire.

Declines in the mammal assemblage of a rugged sandstone environment in Kakadu National Park, Northern Territory, Australia

There has been marked recent decline in the terrestrial mammal fauna across much of northern Australia, with most documentation of such decline for lowland areas. Here we report changes in the assemblage of small mammals in a rugged sandstone environment (Nawurlandja, in Kakadu National Park) over intermittent sampling between 1977 and 2002. Four native mammal species were commonly recorded in the original sampling: sandstone antechinus (Pseudantechinus bilarni), northern quoll (Dasyurus hallucatus), Arnhem rock-rat (Zyzomys maini) and common rock-rat (Z. argurus). Trap success rates declined significantly for the northern quoll, Arnhem rock-rat and all species combined, but increased for the common rock-rat. Despite being recorded commonly in the initial (1977–79) study, no Arnhem rock-rats were recorded in the most recent (2002) sampling. Trap success rates for northern quoll declined by ~90% from 1977–79 to 2002. The reasons for change are not clear-cut. Notably, all sampling occurred before the arrival of cane toads (Rhinella marina), a factor that has caused severe decline in northern quoll numbers elsewhere. Fire was more frequent in the sampling area in the period preceding the 2002 sampling than it was in the period preceding the initial (1977–79) sampling, and this may have contributed to change in mammal abundance.

Pyrodiversity is the coupling of biodiversity and fire regimes in food webs

Fire positively and negatively affects food webs across all trophic levels and guilds and influences a range of ecological processes that reinforce fire regimes, such as nutrient cycling and soil development, plant regeneration and growth, plant community assembly and dynamics, herbivory and predation. Thus we argue that rather than merely describing spatio-temporal patterns of fire regimes, pyrodiversity must be understood in terms of feedbacks between fire regimes, biodiversity and ecological processes. Humans shape pyrodiversity both directly, by manipulating the intensity, severity, frequency and extent of fires, and indirectly, by influencing the abundance and distribution of various trophic guilds through hunting and husbandry of animals, and introduction and cultivation of plant species. Conceptualizing landscape fire as deeply embedded in food webs suggests that the restoration of degraded ecosystems requires the simultaneous careful management of fire regimes and native and invasive plants and animals, and may include introducing new vertebrates to compensate for extinctions that occurred in the recent and more distant past.

This article is part of the themed issue ‘The interaction of fire and mankind’.

Prescribed burning consumes key forest structural components: implications for landscape heterogeneity

Prescribed burning to achieve management objectives is a common practice in fire-prone regions worldwide. Structural components of habitat that are combustible and slow to develop are particularly susceptible to change associated with prescribed burning. We used an experimental, "whole-landscape" approach to investigate the effect of differing patterns of prescribed burning on key habitat components (logs, stumps, dead trees, litter cover, litter depth, and understorey vegetation). Twenty-two landscapes (each ~100 ha) were selected in a dry forest ecosystem in southeast Australia. Experimental burns were conducted in 16 landscapes (stratified by burn extent) while six served as untreated controls. We measured habitat components prior to and after burning. Landscape burn extent ranged from 22% to 89% across the 16 burn treatments. With the exception of dead standing trees (no change), all measures of habitat components declined as a consequence of burning. The degree of loss increased as the extent to which a landscape was burned also increased. Prescribed burning had complex effects on the spatial heterogeneity (beta diversity) of structural components within landscapes. Landscapes that were more heterogeneous pre-fire were homogenized by burning, while those that were more homogenous pre-fire tended to display greater differentiation post-burning. Thus, the notion that patch mosaic burning enhances heterogeneity at the landscape-scale depends on prior conditions. These findings have important management implications. Where prescribed burns must be undertaken, effects on important resources can be moderated via control of burn characteristics (e.g., burn extent). Longer-term impacts of prescribed burning will be strongly influenced by the return interval, given the slow rate at which some structural components accumulate (decades to centuries). Management of habitat structural components is important given the critical role they play in (1) provision of habitat resources for diverse organisms, (2) retention of moisture and nutrients in otherwise dry, low-productivity systems, and (3) carbon storage.

Deriving Multiple Benefits from Carbon Market-Based Savanna Fire Management: An Australian Example

Carbon markets afford potentially useful opportunities for supporting socially and environmentally sustainable land management programs but, to date, have been little applied in globally significant fire-prone savanna settings. While fire is intrinsic to regulating the composition, structure and dynamics of savanna systems, in north Australian savannas frequent and extensive late dry season wildfires incur significant environmental, production and social impacts. Here we assess the potential of market-based savanna burning greenhouse gas emissions abatement and allied carbon biosequestration projects to deliver compatible environmental and broader socio-economic benefits in a highly biodiverse north Australian setting. Drawing on extensive regional ecological knowledge of fire regime effects on fire-vulnerable taxa and communities, we compare three fire regime metrics (seasonal fire frequency, proportion of long-unburnt vegetation, fire patch-size distribution) over a 15-year period for three national parks with an indigenously (Aboriginal) owned and managed market-based emissions abatement enterprise. Our assessment indicates improved fire management outcomes under the emissions abatement program, and mostly little change or declining outcomes on the parks. We attribute improved outcomes and putative biodiversity benefits under the abatement program to enhanced strategic management made possible by the market-based mitigation arrangement. For these same sites we estimate quanta of carbon credits that could be delivered under realistic enhanced fire management practice, using currently available and developing accredited Australian savanna burning accounting methods. We conclude that, in appropriate situations, market-based savanna burning activities can provide transformative climate change mitigation, ecosystem health, and community benefits in northern Australia, and, despite significant challenges, potentially in other fire-prone savanna settings.