Exploring the future of fuel loads in Tasmania. Shifts in vegetation in response to changing fire weather, productivity, and fire frequency

Abstract

Vegetation mediates the interaction between fire and climate, since one of the key determinants of fire activity is the available fuel load. The fuel load is influenced by the structure and composition of the vegetation community, fuel age, rates of decomposition, and vegetation growth rates. Attempts to project future fire danger must therefore account for changes in vegetation growth and fuel dynamics under future climatic conditions. Estimating fuel load under future conditions is complicated by the interactions that exist between the fire regime, vegetation, climate and human intervention. Feedbacks between these factors can lead to changes in the vegetation, which in turn influence the fire regime. Changes to the frequency of fire due to management decisions (eg. Prescribed burning or fire suppression) and climate change have the potential to affect the flammability of the vegetation, with long term effects on the vegetation structure and composition. Frequent fire in some vegetation types can lead to transformational change when a threshold is crossed, beyond which the vegetation type is radically altered, and this is not always a gradual process. These represent major challenges to projecting fuel loads under future climatic conditions. However, it is possible to project several important factors determining fire activity into the future. In Tasmania, values for future climate conditions, including fire weather, Soil Dryness Index and productivity are available from a dynamically downscaled climate model (the Climate Futures for Tasmania projections). For other ecological factors, general trends can be estimated (e.g. growth rate, time to maturity), allowing potential pathways of change to be identified, starting with the current flammability and sensitivity to fire of broad vegetation types. Prescribed burning regimes are likely to change in the future, in response to shifts in community attitudes (eg. With increased concerns about the health effects of smoke), resourcing, and/or a narrowing window available for burning. For this reason, it is important to explore future potential fire activity under different scenarios of fire frequency. We identify the main drivers of change to potential fire activity under future climate change in Tasmania, and explore potential pathways of change to broad vegetation types affecting flammability across the landscape. We use a modelling approach to consider multiple transitional pathways that may occur under different fire frequencies. The model is not a predictive model of vegetation flammability or spread under future conditions. Rather, it is a tool to illustrate the potential impacts of climate change (described here using the Climate Futures for Tasmania projections), in combination with the influence of management decisions about frequency of prescribed burning. Within the model, ecological theory is translated into visualizations and summaries of potential landscape-scale change, enabling the impact of fire frequency on vegetation type and potential future fire activity to be considered. The pathway approach could be used as a tool in community adaptation, to frame potential futures, and identify the consequences of decisions seeking to manage fire risk in the future. Change over time, under different management regimes (frequency of prescribed burning), can be spatially represented to show the shifts in vegetation type, and hence flammability, across Tasmania.