Climate change‐induced shifts in fire for M editerranean ecosystems

Abstract

Aim: Pyrogeographical theory suggests that fire is controlled by spatial gradients in resources to burn (fuel amount) and climatic conditions promoting combustion (fuel moisture). Examining trade‐offs among these environmental constraints is critical to understanding future fire activity. We evaluate constraints on fire frequency in modern fire records over the entire Mediterranean biome and identify potential shifts in fire activity under an ensemble of global climate projections. Location: The biome encompassing the M editerranean‐type ecosystems (MTE s). Methods: We evaluate potential changes in fire over the 21st century in MTE s based on a standardized global framework. Future fire predictions are generated from statistical fire−climate models driven by ensembles of climate projections under the IPCC A2 emissions scenario depicting warmer–drier and warmer–wetter syndromes. We test the hypothesis that MTE s lie in the transition zone discriminating fuel moisture versus fuel amount as the dominant constraint on fire activity. Results: Fire increases reported in MTE s in recent decades may not continue throughout the century. MTE s occupy a sensitive portion of global fire−climate relationships, especially for precipitation‐related variables, leading to highly divergent fire predictions under drier versus wetter syndromes. Warmer–drier conditions could result in decreased fire activity over more than half the Mediterranean biome by 2070–2099, and the opposite is predicted under a warmer–wetter future. MTE s encompass, however, a climate space broad and complex enough to include spatially varied fire responses and potential conversions to non‐MTE biomes. Main conclusions: Our results strongly support the existence of both fuel amount and fuel moisture constraints on fire activity and show their geographically variable influence throughout MTE s. Climatic controls on fire occurrence in MTE s lie close to ‘tipping points’, where relatively small changes in future climates could translate into drastic and divergent shifts in fire activity over the Mediterranean biome, mediated by productivity alterations.