Fire disturbance and climate change: Implications for Russian forests

Change in the Russian boreal forest has the capacity to alter global carbon and climate dynamics. Fire disturbance is an integral determinant of the forest's composition and structure, and changing climate conditions are expected to create more frequent and severe fires. Using the individual tree-based forest gap model UVAFME, along with an updated fire disturbance module that tracks mortality based on tree-species and-size level effects, biomass and species dynamics are simulated across Russia for multiple scenarios: with and without fire, and with and without altered climate. Historical fire return intervals and percent of forest stand mortality are calculated for the Russian eco-regions and applied to 31 010 simulation points across Russia. Simulation results from the scenarios are compared to assess changes in biomass, composition, and stand structure after 600 years of successional change following bare-ground initiation. Simulations that include fire disturbance show an increase in biomass across the region compared to equivalent simulations without fire. Fire disturbance allows the deciduous needle-leaved conifer larch to maintain dominance across much of the region due to their high growth rate and fire tolerance relative to other species. Larch remain dominant under the scenario of altered climate conditions with fire disturbance. The distribution of age cohorts shifts for the scenario of altered climate with fire disturbance, displaying a bimodal distribution with a peak of 280-year-old trees and another of 100-year-old cohorts. In these simulations, fire disturbance acts to increase the turnover rate and patterns of biomass accumulation, though species and tree size are also important factors in determining mortality and competitive success. These results reinforce the importance of the inclusion of complex competition at the species level in evaluating forest response to fire and climate.