Cameron Yates

Bushfires 'down under': patterns and implications of contemporary Australian landscape burning

Australia is among the most fire-prone of continents. While national fire management policy is focused on irregular and comparatively smaller fires in densely settled southern Australia, this comprehensive assessment of continental-scale fire patterning (1997-2005) derived from ∼ 1k m 2 AdvancedVery High Resolution Radiometer (AVHRR) imagery shows that fire activity occurs predominantly in the savanna landscapes of monsoonal northern Australia. Sta- tistical models that relate the distribution of large fires to a variety of biophysical variables show that, at the continental scale, rainfall seasonality substantially explains fire patterning. Modelling results, together with data concerning seasonal lightning incidence, implicate the importance of anthropogenic ignition sources, especially in the northern wet-dry tropics and arid Australia, for a substantial component of recurrent fire extent. Contemporary patterns differ markedly from those under Aboriginal occupancy, are causing significant impacts on biodiversity, and, under current patterns of human popula- tion distribution, land use, national policy and climate change scenarios, are likely to prevail, if not intensify, for decades to come. Implications of greenhouse gas emissions from savanna burning, especially seasonal emissions of CO2, are poorly understood and contribute to important underestimation of the significance of savanna emissions both in Australian and probably in international greenhouse gas inventories. A significant challenge for Australia is to address annual fire extent in fire-prone Australian savannas.

Big fires and their ecological impacts in Australian savannas: size and frequency matters

Savannas are the most fire-prone of the earth’s major biomes. The availability of various broad-scale satellite-derived fire mapping and regional datasets provides a framework with which to examine the seasonality, extent and implications of large fires with particular reference to biodiversity values in the tropical savannas of northern Australia. We document the significance of savanna fires in the fire-prone ‘Top End’ region of the Northern Territory, Australia, using 9 years (1997–2005) of National Oceanic and Atmospheric Administration (NOAA)-Advanced Very High Resolution Radiometer (AVHRR)-, Landsat Thematic Mapper (TM)- and Enhanced Thematic Mapper (ETM+)-derived fire mapping. Fire (patch) sizes from both AVHRR- and Landsat-scale mapping increased through the calendar year associated with progressive curing of grass and litter fuels. Fire frequency data at both satellite sensor scales indicate that regional fire regimes in higher rainfall regions are dominated by large (>1000 km2) fires occurring typically at short (~2–3 years) fire return intervals. In discussion, we consider the ecological implications of these patch size distributions on regional fire-sensitive biota. Collectively, assembled data illustrate that many northern Australian savanna flora, fauna and habitats embedded within the savanna matrix are vulnerable to extensive and frequent fires, especially longer-lived obligate seeder plant taxa and relatively immobile vertebrate fauna with small home ranges.

Patterns of landscape fire and predicted vegetation response in the North Kimberley region of Western Australia

The paper reports on the development of a decadal fire history, 1990–1999, derived from Landsat imagery, and associated assessment of landscape-scale patterns, in a remote, sparsely human-populated region of the high rainfall zone of monsoonal north-western Australia. The assembled fire history confirms observations, derived from coarser-scale imagery, that substantial areas of the North Kimberley are burnt each year. The annual mean extent of burning was 31% (albeit involving marked inter-annual variability), with most burning occurring in the latter part of the dry season under relatively severe fire weather conditions. Extent of burning was found to be associated with intensity of landuse; most burning occurred on pastoral lands, particularly in association with more fertile basalt soils. Based on previous modelling studies, predicted effects of contemporary fire regimes include increased development of woody regeneration size-classes, especially on non-basalt substrates. In contrast, on sandstone-derived substrata, fire interval data indicate that longer-lived obligate-seeder shrub species are likely to be suppressed and ultimately displaced by contemporary fire regimes. Such observations are supported by recent evidence of regional collapse of the long-lived obligate seeder tree species, Callitris intratropica. Collectively, assembled data point to the need to undertake a thorough appraisal of the status of regional biota in this remote, ostensibly ecologically intact region.

Fire regimes and interval-sensitive vegetation in semiarid Gregory National Park, northern Australia

Few data are available concerning contemporary fire regimes and the responses of fire interval-sensitive vegetation types in semiarid woodland savanna landscapes of northern Australia. For a 10 300 km2 semiarid portion of Gregory National Park, in the present paper we describe (1) components of the contemporary fire regime for 1998–2008, on the basis of assessments derived from Landsat and MODIS imagery, (2) for the same period, the population dynamics, and characteristic fine-fuel loads associated with Acacia shirleyi Maiden (lancewood), an obligate seeder tree species occurring in dense monodominant stands, and (3) the fire responses of woody species, and fine-fuel dynamics, sampled in 41 plots comprising shrubby open-woodland over spinifex hummock grassland. While rain-year (July–June) rainfall was consistently reliable over the study period, annual fire extent fluctuated markedly, with an average of 29% being fire affected, mostly in the latter part of the year under relatively harsh fire-climate conditions. Collectively, such conditions facilitated short fire-return intervals, with 30% of the study area experiencing a repeat fire within 1 year, and 80% experiencing a repeat fire within 3 years. Fine fuels associated with the interior of lancewood thickets were characteristically small ( 10 years. Of 133 woody species sampled, all trees (n = 26), with the exception of A. shirleyi, were resprouters, and 58% of all shrub species (n = 105) were obligate seeders, with observed primary juvenile periods <5 years. Assembled data generally supported observations made from other northern Australian studies concerning the responses of fire-sensitive woody taxa in rugged, sandstone-derived landscapes, and illustrated the enormous challenges facing ecologically sustainable fire management in such settings. Contemporary fire regimes of Gregory National Park are not ecologically sustainable.

Fire regimes and soil erosion in north Australian hilly savannas

Soil erosion is recognised as a major landscape management issue in northern Australia, given highly erodible soils, and high rainfall erosivity associated with low soil surface cover and intense storm events at the commencement of the wet season. Although recent continental-scale erosion modelling addresses such conditions, it does not take account of contemporary fire regimes dominated by annual, late dry season wildfires, especially in extensive higher slope (≥5%) regions of monsoonal Australia. The present paper reports a simple erosion pin assessment at two sites, contrasting soil loss and movement on unburnt and late dry season-burnt hillslopes over one wet season. Although very significant erosion was observed on both unburnt and burnt treatments, overall there was roughly three times the net soil loss and two times more soil movement on late dry season-burnt plots. The landscape scale of late dry season fire regimes, and implications for increased impacts of soil erosion on soil organic matter, nutrients, and ecosystem health are discussed. Collectively, assembled data suggest that more attention needs to be given to understanding and managing the impacts of contemporary fire regimes on hillslope soil erosion processes in the seasonal Australian tropics.

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.

Fire patterns in north Australian savannas: extending the reach of incentives for savanna fire emissions abatement

Anthropogenic fires in Australia’s fire-prone savannas produce up to 3% of the nation’s accountable greenhouse gas (GHG) emissions. Incentives to improve fire management have been created by a nationally accredited savanna burning emissions abatement methodology applying to 483 000 km2 of relatively high-rainfall (>1000 mm p.a.) regions. Drawing on 15 years of fire mapping, this paper assesses appropriate biophysical boundaries for a savanna burning methodology extended to cover lower-rainfall regions. We examine a large random sample of points with at least 300 mm of annual rainfall, to show that: (a) relative fire frequencies (percentage of years with fire) decline from 33.3% in higher-rainfall regions (>1000 mm) to straddling ~10% in the range 300–700 mm; (b) there are no marked discontinuities in fire frequency or fire seasonality down the rainfall gradient; (c) at all annual rainfalls, fire frequency is higher when rainfall is more strongly seasonal (very low rainfall in the driest quarter); (d) below 500 mm fire regimes are particularly variable and a large proportion of sampled sites had no fire over the study period; (e) fire is more likely to occur later in the fire season (generating relatively higher emissions) in the 600–700-mm annual rainfall band than in other parts of the rainfall gradient; (f) woodland savannas are most common above and predominantly grassland systems are more common below ~600-mm annual rainfall. We propose that development of a complementary lower-rainfall savanna burning methodology apply to regions between 600 and 1000-mm annual rainfall and ≤15 mm of rainfall in the driest quarter, adding an area more than 1.5 times the existing methodology’s coverage. Given greater variability in biophysical influences on fire regimes and observed levels of fire frequency within this lower-rainfall domain, we suggest that criteria for determining baseline (pre-project) periods require estimates of mean annual emissions equivalent in precision to the project on which the higher-rainfall methodology was based.