Abstract
Forest die-offs associated with drought and heat have recently occurred across the globe, raising concern that associated changes in fuels and microclimate could link initial die-off disturbance to subsequent fire disturbance. Despite widespread concern, little empirical data exist. Following forest die-off in the Northern Jarrah Forest, southwestern Australia, we quantified fuel dynamics and associated microclimate for die-off and control plots. Sixteen months post-die-off, die-off plots had significantly elevated 1-hr fuels (11.8 vs. 9.8 tons ha-1) but not larger activity fuel classes (10-hr and 100-hr fuels). Due to stem mortality, die-off plots had significantly greater standing dead wood mass (100 vs. 10 tons ha-1), visible sky (hemispherical images analysis: 31% vs. 23%) and potential near-ground solar radiation input (measured as Direct Site Factor: 0.52 vs. 0.34). Supplemental, mid-summer microclimate measurements (temperature, relative humidity and wind speed) were combined with long-term climatic data and fuel load estimates to parameterize fire behaviour models. Fire spread rates were predicted to be 30% greater in die-off plots with relatively equal contributions from fuels and microclimate, highlighting need for operational consideration by fire managers. Our results underscore potential for drought-induced tree die-off to interact with subsequent fire under climate change.