Investigating tree species effects on plant-soil-microbial feedbacks in Alaskan boreal forest

In Alaskan boreal forest, fire is a common disturbance that can alter successional trajectories and plant-soil-microbial (PSM) feedbacks. Black spruce (Picea mariana) is the most common tree species in Interior Alaska and is typically associated with slow decomposition rates, a thick organic layer, and a shallow active layer depth. Following severe fires that burn deeply into the organic layer, spruce forest can give way to deciduous stands. Deciduous stands tend to exhibit less recalcitrant leaf litter and reduced forest floor moss cover, which may alter nutrient cycling, organic soil re-accumulation post fire, and insulation of permafrost soils. Forecasts of future climate suggest that the boreal region will experience larger, more severe fires in the coming years, which may lead to increased deciduous forest cover. We are investigating PSM feedbacks in mid-successional black spruce and Alaska paper birch (Betula neoalaskana) stands associated with the Bonanza Creek LTER to improve our understanding of the relationship between fire, vegetation, soils, and permafrost degradation. We hypothesize that paper birch stands will exhibit faster rates of decomposition and carbon and nitrogen cycling, a shallower organic layer, and deeper active layer depth. Additionally, we hypothesize that moss growth is limited in deciduous stands by annual litterfall inputs that blanket the forest floor and smother the mosses. We are currently conducting a moss transplant and litter manipulation experiment to test this hypothesis. Results of this work will provide important insights into how shifts in fire severity influence ecosystem nutrient dynamics, organic matter accumulation, and permafrost thaw.