Drought, topography, and forest management shape wildfire occurrence and severity in montane Australian landscapes

In recent decades, changes in climate and land use have reshaped forest landscapes across the globe, altering the timing and severity of forest fires. This study investigated the influence of climate, landform, forest disturbances, and management on wildfire occurrence and severity in the montane forests of south-eastern Australia. Modelling of spatial data from 1981 to 2020 showed that fire occurrence was highly sensitive to the top-down influence of antecedent drought, whereas fire severity was primarily influenced by bottom-up factors such as topography, past fires, and historical timber harvesting. Below-average rainfall and high vapour pressure deficit, incorporated into a forest drought stress index, were postiviely associated with wildfire occurrence. This relationship between climate and wildfire occurrence varied across ecosystems and was generally stronger in lower elevation montane forests compared to higher elevation areas. Time since the last fire was also influential: forests that had recently burned (e.g., <5 years) or had no history of fire were less likely to burn or experience high severity wildfire. Clearfell harvesting reduced the probability of fire occurrence and high severity fire for several decades post-harvest relative to forests with no recorded harvesting. Topography modulated landscape flammability: fire occurrence and severity increased with steeper slopes and were reduced in moist topographic locations. These findings highlight that climate, landform, and land use are important drivers of fire occurrence and severity in montane forests. Strategic use of prescribed burning, protection of topographic refugia, and assisted forest regeneration could help maintain the structure and composition of montane forests in a more flammable future.