Future Transitions From a Conifer to a Deciduous-Dominated Landscape are Accelerated by Greater Wildfire Activity and Climate Change in Interior Alaska

Context In interior Alaska, increasing wildfire activity associated with climate change is projected to continue, potentially altering regional forest composition. Conifers are emblematic of boreal forest; however, greater frequency and severity of wildfires has been found to favor broadleaf-deciduous species in numerous studies. Objectives This study examines potential shifts in forest type in interior Alaska and how shifts may be impacted by recurring wildfires under future climate change. Methods A spatially-explicit forest landscape model, LANDIS-II, was used to simulate forest succession and wildfire over a 380,400-hectare landscape under historic and future (RCP 8.5) climate. Wildfire was modeled using the SCRPPLE fire extension and vegetation growth, belowground carbon, hydrologic, and permafrost dynamics were modeled with the DGS succession extension. The relative importance of drivers of forest type change away from black spruce was quantified using random forest models for areas on the landscape experiencing different numbers of wildfires. Results Greater frequencies of fire activity were associated with shifts in conifer-dominant areas to broadleaf-deciduous, which climate change accelerated. Vegetation transitions were most strongly influenced by percent tree mortality from the most recent wildfire. Starting deciduous fraction and proximity of mature black spruce to a site pre-fire were also influential, indicating pre-fire composition and context modified the effect of vegetation shifts. Conclusions These results underscore how shifts in forest type may occur in a nonlinear manner in this region as the landscape experiences pressure from climate change and forests are subject to complex interactions between wildfire, climate, belowground processes, and the arrangement of forest communities