Modeling the effects of fire and climate change on carbon and nitrogen storage in lodgepole pine (Pinus contorta) stands

The interaction between disturbance and climate change and resultant effects on ecosystem carbon (C) and nitrogen (N) fluxes are poorly understood. Here, we model (using CENTURY version 4.5) how climate change may affect C and N fluxes among mature and regenerating lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Wats.) stands that vary in postfire tree density following stand-replacing fire. Both young (postfire) and mature stands had elevated forest production and net N mineralization under future climate scenarios relative to current climate. Forest production increased 25% [Hadley (HAD)] to 36% [Canadian Climate Center (CCC)], compared with 2% under current climate, among stands that varied in stand age and postfire density. Net N mineralization increased under both climate scenarios, e.g., + 19% to 37% (HAD) and + 11% to 23% (CCC), with greatest increases for young stands with sparse tree regeneration. By 2100, total ecosystem carbon (live + dead + soils) in mature stands was higher than prefire levels, e.g., + 16% to 19% (HAD) and + 24% to 28% (CCC). For stands regenerating following fire in 1988, total C storage was 0-9% higher under the CCC climate model, but 5-6% lower under the HAD model and 20-37% lower under the Control. These patterns, which reflect variation in stand age, postfire tree density, and climate model, suggest that although there were strong positive responses of lodgepole pine productivity to future changes in climate, C flux over the next century will reflect complex relationships between climate, age structure, and disturbance-recovery patterns of the landscape.