Overriding influence of climate on future carbon stocks in Australian temperate forests

Climate change presents multiple challenges to the stability of forest carbon stocks in fire-prone landscapes, and many uncertainties about landscape-scale carbon-stock trajectories arise from complex interactions among climate, fire regimes and vegetation dynamics. This study examines the relative influences of climate, fire and tree mortality on above-ground carbon-stock trajectories in a landscape dominated by fire-tolerant eucalypt forests to improve understanding of the potential magnitude and source of forest carbon change in temperate Australia. We apply a unique spatially explicit modelling framework that couples a stochastic fire regime simulation tool (FROST) with a vegetation dynamics model (LANDIS-II) to test the relative influence of three mechanisms on forest carbon at landscape scales: heat and dryness, more frequent severe fire, and elevated post-fire tree mortality. Simulations involved 16 modelled scenarios (4 climate projections × 2 wildfire levels × 2 tree fire tolerances) across a 600,000-ha landscape for a period of 78 years (2020 to 2098). Predicted outcomes for above-ground carbon stocks across the scenarios ranged from mean increases of 16 % to substantive decreases of 50 % by 2098, with the greatest threat posed by the combined effects of heat and dryness through intensified fire regimes (more frequent, more intense fires) and reduced forest productivity. The results of our simulations highlight the importance of mitigating climate change, where it involves warming plus drying, to sustaining carbon stores in temperate forests. Without effective climate-change mitigation, the security of temperate forest carbon stocks will increasingly depend on limiting the extent and frequency of severe wildfires and minimising tree mortality from wildfire and other landscape-scale disturbances.