Karen J. King

The relative importance of fine-scale fuel mosaics on reducing fire risk in south-west Tasmania, Australia

In many landscapes, an important fire management objective is to reduce the negative impacts from unplanned fires on people, property and ecological values. In Australia, there exists an inherent assumption that high spatial variability in fire ages and hence fuel loads will have negative effects on both the incidence and spread of subsequent fires, and will enhance ecological values. A recent study using the process-based computer simulation model FIRESCAPE-SWTAS predicted several relationships between prescribed burn treatment levels and spatial patterning and management objectives in south-west Tasmania, Australia. The present study extended this investigation to additionally explore the effects of prescribed burning treatment unit size on unplanned fire incidence and area burned both in the general landscape and specifically in fire-intolerant vegetation. Simulation results suggest that treatment level had the greatest influence on modifying fire effects, whereas treatment unit size had the least effect. The model predicted that all three parameters interacted to determine the mean annual area burnt by unplanned fires. In fire-intolerant vegetation, treatment unit size did not influence the incidence of unplanned fires and the area burnt by unplanned fires in these communities. Where significant differences were evident, fire risk was reduced by higher treatment levels, deterministic spatial patterns of burning units, and smaller burning unit sizes.

Simulation of prescribed burning strategies in south-west Tasmania, Australia: effects on unplanned fires, fire regimes, and ecological management values

Computer simulation modelling provides a useful approach for determining the trade-offs between the extent of prescribed burning and the long-term impacts of unplanned fires on management values. In the present study, FIRESCAPE-SWTAS, a process-based fire regime and vegetation dynamics model, was used in the World Heritage Area of south-west Tasmania, Australia, to investigate the implications of different prescribed burning treatments on identified management objectives. Treatments included annual prescribed burning of different proportions of the most flammable vegetation community, buttongrass moorlands. Additionally, a proposed strategic burning treatment for this landscape was simulated for comparison with these treatments. Simulations identified the nature of the relationships between the prescribed burn treatment level and the fire size distributions, the mean incidence, and the mean annual areas burnt by unplanned fires, with all three parameters declining with increases in treatment level. The study also indicated that strategically located treatment units were able to enhance the reduction in the fire risk to vegetation species susceptible to fire (fire-intolerant species).

Contrasting fire responses to climate and management: insights from two Australian ecosystems.

This study explores effects of climate change and fuel management on unplanned fire activity in ecosystems representing contrasting extremes of the moisture availability spectrum (mesic and arid). Simulation modelling examined unplanned fire activity (fire incidence and area burned, and the area burned by large fires) for alternate climate scenarios and prescribed burning levels in: (i) a cool, moist temperate forest and wet moorland ecosystem in south-west Tasmania (mesic); and (ii) a spinifex and mulga ecosystem in central Australia (arid). Contemporary fire activity in these case study systems is limited, respectively, by fuel availability and fuel amount. For future climates, unplanned fire incidence and area burned increased in the mesic landscape, but decreased in the arid landscape in accordance with predictions based on these limiting factors. Area burned by large fires (greater than the 95th percentile of historical, unplanned fire size) increased with future climates in the mesic landscape. Simulated prescribed burning was more effective in reducing unplanned fire activity in the mesic landscape. However, the inhibitory effects of prescribed burning are predicted to be outweighed by climate change in the mesic landscape, whereas in the arid landscape prescribed burning reinforced a predicted decline in fire under climate change. The potentially contrasting direction of future changes to fire will have fundamentally different consequences for biodiversity in these contrasting ecosystems, and these will need to be accommodated through contrasting, innovative management solutions.

Fire and carbon dynamics under climate change in south-eastern Australia: insights from FullCAM and FIRESCAPE modelling

This study used simulation modelling to investigate fire and carbon dynamics for projected warmer and drier climates in the south-eastern Australian high country. A carbon accounting model FullCAM and the landscape fire regime simulator FIRESCAPE were combined and used to simulate several fire management options under three climate scenarios – the recent climate (1975–2005); a moderate climate projected for 2070 (B1); and a more extreme climate projected for 2070 (A1FI). For warmer and drier climates, model simulations predicted (i) an increase in fire incidence; (ii) larger areas burned; (iii) higher mean fire intensities; (iv) shorter fire cycle lengths; (v) a greater proportion of fires burning earlier in the fire season; (vi) a reduction in carbon stores; (vii) a reduction in carbon sequestration rates; and (viii) an increase in the proportion of stored carbon emitted to the atmosphere. Prescribed burning at historical or twice historical levels had no effect on fire or carbon dynamics. In contrast, increasing the initial attack success (a surrogate for suppression) partially offset the adverse effects of warmer and drier climates on fire activity, but not on carbon dynamics. For the south-eastern Australian high country, simulations indicated that fire and carbon dynamics are sensitive to climate change, with simulated fire management only being able to partially offset the adverse effects of warmer and drier climate.

Australian grassland fire danger using inputs from the GRAZPLAN grassland simulation model

Assessing and broadcasting the Fire Danger Rating each day of the fire season is an important activity in fire-prone nations. For grasslands in Australia, grass curing and biomass are biological variables that are not usually archived yet as inputs, along with weather data, to the calculation of Grassland Fire Danger Index (GFDI) and potential fire intensity. To assess past changes in the index, the biological inputs for GFDI for Canberra in south-eastern Australia were obtained using a pasture simulator, GRAZPLAN. Shoot biomass (including leaf litter) and grass curing were modelled using three contrasting pasture models (exotic annual, exotic perennial and native perennial) in order to calculate two variants of McArthur’s GFDI Mark 4 (the original and a modified version which includes fuel load); values were either capped at 100 as in the original (the ‘worst possible’ condition) or left open-ended. GFDI, and the potential fire intensity for fires burning with the wind each afternoon during a 54-year period were calculated. The native perennial grass model gave contrasting results to those from the exotic perennial grass model, whereas the annual grass model usually was intermediate in behaviour. GRAZPLAN outputs allow not only retrospective examination, but also provide a basis for predicting potential fire danger and behaviour as a result of climate change.

Implications of changing climate and atmospheric CO 2 for grassland fire in south-east Australia: insights using the GRAZPLAN grassland simulation model

Climate and fuel characteristics influence fire regimes, and both need to be realistically considered in bushfire projections. Previous south-eastern Australian studies have assumed maximum grassland fuel curing (100%) and average fuel load (4.5 t ha–1). This study is the first to include daily fuel curing and load dynamics, derived from the agricultural pasture growth model GRAZPLAN, in projections of Grassland Fire Danger Index (GFDI) and potential fire-line intensity for future climate–CO2 combinations, and for alternate grasslands in the Canberra, Sydney and Melbourne regions. Climate-change projections were characterised by warmer, drier conditions, with atmospheric CO2 concentrations increasing for longer future timeframes. Projected shifts in GFDI and potential fire-line intensity arising from future climate–CO2 combinations were small compared with initial difference arising from using realistic GRAZPLAN-derived curing and fuel load values (compared with constant curing and fuel load) for grass dynamics, and this has important implications for the interpretation of earlier studies. Nevertheless, future grass curing and GFDI generally increased and fuel load generally decreased. The net effect on modelled future fire-line intensity was minimal because higher fire danger, and hence spread rate, was often largely compensated for by lower fuel load across the range of modelled grassland types and locations.