Avian responses to the diversity and configuration of fire age classes and vegetation types across a rainfall gradient

Abstract

In many regions, planned burns are implemented to reduce fuel loads and mitigate wildfire risk; increasingly, they are also used to achieve conservation outcomes. However, there is uncertainty regarding how best to apply fire to landscapes in order to enhance biodiversity. The assumption that variable fire regimes are conducive to biodiversity conservation is appealing given its basis in landscape ecological theory, which predicts that spatially complex landscapes sustain greater biodiversity. This supposition is often used as a basis for fire management but has rarely been tested in the context of fire. We sought to test predicted positive relationships between bird diversity and both landscape diversity and configuration in the fire-prone Otway Ranges, southeast Australia, where vegetation transitions from treeless heath to tall open eucalypt forest across a rainfall gradient. We used a whole-of-landscape sampling approach, and mapped fire age classes and vegetation types separately within thirty-six 300ha landscape sampling units. Bird surveys were undertaken at sub-sampling locations during two successive years, and presence-absence data were used to generate landscape-level estimates of species richness and turnover. Generalized linear mixed models, model selection and model averaging were used to investigate how birds responded to landscape diversity and configuration across the rainfall gradient. Species richness was positively associated with age class diversity, age class configuration and vegetation type diversity. Species turnover was positively associated with age class diversity in areas of lower rainfall but exhibited a negative response in areas of higher rainfall. Neither response variable was associated with vegetation type configuration. This study is one of few landscape scale analyses to provide empirical support for the widely held assumption that spatially variable fire regimes can increase the diversity of faunal assemblages. Further, our results demonstrated consistency in responses of species richness to fire-mediated landscape complexity across a rainfall gradient. Managers can potentially increase bird species richness by increasing both the diversity of fire age classes, and the complexity of age class configuration, within relatively small (300ha) areas.