Predicting fire regimes and their ecological effects in spatially complex landscapes

Abstract

Fire occurrence influences the distribution of plant species, and dynamics of plant populations, either independently from other factors or in interaction with them. Numerous studies have identified the effects of components of fire regimes (frequency, intensity and season of occurrence) on the population dynamics of individual plant species and the floristic composition of plant communities, both in Australia and in other fire-prone countries. Nevertheless, there has been considerably less research into understanding the causes of spatial variation in fire regimes and this will likely result in a major obstacle for the development of vegetation theory. Research into spatial and temporal patterns of fire regime and determining the extent to which this type of variation results in variation in the occurrence of plant species and hence the composition of plant communities, can help overcome this obstacle. Two hypotheses are constructed and addressed. They are:- (i) that because of the influence of a sites' neighbourhood, variation in fire regimes will exist for any particular set of sites that occupy a particular part of environmental space and are therefore otherwise similar, and (ii) that this variation in fire regimes will result in patterns of plant species occurrence and hence demonstrate that landscape induced pattems of fire regime are a fundamentally important component in determining the realised niche of plant species in spatially complex landscapes. These hypotheses are examined for a spatially complex landscape in the Australian Capital Territory region, Australia. Several distinct phases of research led to the conclusion that both hypotheses should be accepted for the study region. Firstly, a review of the available literature found that empirical approaches, and related statistical models, for determining long-term fire regimes provided data that was neither of sufficient length and accuracy nor of appropriate spatial resolution for examining landscape dependent patterns in fire regimes as outlined in hypothesis one. On the other hand, theoretical approaches which synthesise landscape patterns from the well­ understood processes that affect fire occurrence and behaviour proved to be a useful methodology, provided that the inadequacies in existing models, including their reliance on the North American approach to modelling fire spread, were addressed. These provisions were addressed by the construction of a new landscape-level process­ based dynamic simulation model known as FIRESCAPE. The development of the model involved parameterising and testing the Richardson weather generator for fire danger modelling and a re-assessment of the McRae lightning ignition model. The approach used in FIRESCAPE combines these models with existing models of terrain, solar radiation budgets, fuel moisture, soil moisture, fuel accumulation and fire spread to model spatial variation in fire regimes by the accumulation of information from spatially and temporally distinct fire events. Various analyses indicated that…