The Impacts of Fire on Plant Stoichiometry and Nitrogen Cycling in the Yukon-Kuskokwim Delta, AK

In the wake of a changing and warming climate, the Arctic is experiencing the most dynamic increase of average surface temperature globally, which is expected to increase the frequency of wildfires in the region. Wildfires are changing the biogeochemical functions of the Arctic ecosystem; however, this change is not fully understood. To address these uncertainties, we surveyed three replicates of 30cm² plots of aboveground biomass at four 2015 burn sites and one 1972 burn site, that were paired with four unburned (control) sites in the Yukon-Kuskokwim (YK) Delta, AK. The aboveground biomass was divided into species and functional type, and shrubs were sub-sorted into parts (leaves, stems, and flowers). All aboveground biomass was analyzed for % carbon (C), % nitrogen (N), and C:N.

In the 2015 burn sites, the aboveground biomass had not recovered relative to the control sites, and plant biomass and composition in the 1972 burn site were also significantly different from control sites. The C:N of the shrub leaves and stems from the 2015 burn site was significantly reduced. Yet, after more than four decades of recovery post-burn, shrub leaf and stem C:N were comparable to control sites. We also found that even 46 years after the 1972 burn that the wildfire was still having an effect on the landscape, where shrub biomass (and thus g C and N stored in shrubs) were greater than the control sites. These findings indicate that fire may facilitate a positive feedback of N and nutrient cycling even decades after the fire; this alteration to the YK Delta and other arctic tundra regions could become even more prevalent with the increasing frequency of wildfires.