Vegetation, terrain and fire history shape the impact of extreme weather on fire severity and ecosystem response

Abstract

Questions: Do endogenous (landscape/vegetation) or exogenous (weather) factors control fire severity? During severe fire weather, is there convergence in fire severity across rain forest, forests and heathlands such that all locations burn with similarly high severity? Are there long-term effects of fire severity in temperate crown-fire ecosystems? Location: Montane rain forests, eucalypt forests and heaths in the temperate climate zone of eastern Australia (Washpool/Gibraltar Range National Park). Methods: The immediate and longer-term effects of fire weather and landscape (terrain, previous fire history and vegetation type) factors on fire severity and ecosystem response were measured using remote sensing and ground measures of microclimate, productivity and plant resprouting at 45 sites. Results: Fire weather strongly interacted with terrain, antecedent fire history and vegetation type, resulting in complex mosaics of mixed fire severity rather than convergence to uniform fire severity. Vegetation type influenced the effects of time-since-fire and fire frequency on fire severity, suggesting differential fire feedbacks. High fire severity left a long-term imprint on total reflectance, ground temperatures and productivity of the vegetation, but these effects were not uniform across vegetation types. The abundance of resprouting species was not strongly affected by fire severity. Conclusions: There was evidence for strong weather control of fire severity but fire history, terrain and vegetation shape the immediate effect due to the contrasting pyrogenic vs pyrophobic nature of the vegetation mosaic. The short-term dominance of weather as a driver of fire severity is only weakly related to the longer-term ecosystem response because of the strong resprouting ability of the canopy dominants, even in rain forest. The forest complexes of eastern Australia appear highly resilient to high fire severity in both structure and floristics, which may influence long-term feedbacks.