Boreal ecosystems stretch across the northern portion of the world, containing more land area and carbon than any other terrestrial biome. This ecosystem is facing multiple threats from climate change and increasing wildfires, but models seldom capture critical feedbacks among fire, vegetation, and soil that are important in boreal forests. We established a fire frequency gradient (burned 1X, burned 2X, and burned 3X) at two sites in Interior Alaska and examined how fire frequency affects successional trajectories and soil C cycling. Results from these field studies were integrated into a new modeling framework to simulate how climate change and wildfire affect species composition (LANDIS-II), permafrost (GIPL), hydrology (SHAW), and carbon and nitrogen cycling (DAMM-MCNiP).
Results/Conclusions
In both our field and modeling studies, we found that conifer regeneration was significantly lower in 3X burns than 1X burns, but hardwood regeneration was consistent across the burn frequencies. In the 2X and 3X burns, organic matter depth was reduced and both total and heterotrophic soil respiration were elevated, likely due to the higher soil temperatures, live root biomass, and lability of deciduous litter in the field. Soil organic matter from deeper soil layers was more easily decomposed than surface SOM, suggesting permafrost thaw could stimulate greater C loss than predicted from surface temperatures alone. Modeling efforts that integrate wildfire, permafrost, hydrology and species dynamics are essential for projecting non-analog species assemblages, feedbacks, and carbon dynamics in boreal forests.