Drivers of diversity at the local- and landscape-scale in a fire-prone landscape

Abstract

Determining the factors that generate and maintain patterns of biodiversity is a challenge central to ecology. To effectively manage heterogeneous landscapes for biodiversity conservation there is a need to understand the mechanisms driving the relationship between spatial heterogeneity and species richness at multiple scales. Disturbances such as fire affect landscape heterogeneity and are important influences on the distribution and abundance of biota across a range of scales. A key challenge for biodiversity conservation in fire-prone ecosystems is thus to understand the influence of fire on biotic communities.Contemporary ecological fire management resounds with the term 'pyrodiversity'. Efforts to achieve pyrodiversity are usually motivated by the rationale that increasing gamma diversity relies upon maintaining a mosaic of patches of different fire histories. From a global review of literature, this thesis revealed that despite widespread acceptance of this paradigm, the evidence supporting it is extremely sparse. This dearth of knowledge of how heterogeneity affects biota limits effective application of the mosaic burning approach. Studies that consider the spatial and temporal attributes of the fire regime mosaic, and investigate the relationship between these and multiple taxa at different spatial scales, are urgently required.To respond to this knowledge gap, this thesis investigated the effects of fire history and habitat heterogeneity on structure and composition of floral and avifaunal communities. This thesis tests hypotheses about the importance of variable fire regimes, spatial heterogeneity, extent of habitat, and local-and landscape-responses on birds and their habitat in the fire-prone sub-tropical woodlands of central Queensland. Two methods were used to collect the data: i) digital mapping and characterisation of the fire regime mosaic; and ii) surveys of woody vegetation and avifaunal communities.The post-fire response of vegetation reflects not only a single fire event but is the result of cumulative effects of previous fires in the landscape. Fire history categories based on unique combinations of time since last burn, fire frequency and season of last burn were developed and used to map the fire regime mosaic of the study area. This thesis establishes that fire history category strongly influences richness and abundance of mid-storey trees and of individual plants currently comprising the mid-level strata. The particular elements of fire history, time since fire and fire frequency, had the strongest influence on vegetation structure. A longer time since fire (> 4 years since last burn) combined with infrequent fires (< 2 fires in 12 year period) appeared to iii promote a dense mid-storey with the opposite conditions promoting more-open woodlands. This is of particular relevance for conservation management of woodland birds that have been shown to respond strongly to habitat structural variables in the study area.Landscape heterogeneity and extent of habitat are each expected to c...