Interactions among vegetation, climate, and herbivory control greenhouse gas fluxes in a subarctic coastal wetland

High-latitude ecosystems are experiencing the most rapid climate changes globally, and in many areas these changes are concurrent with shifts in patterns of herbivory. Individually, climate and herbivory are known to influence biosphere-atmosphere greenhouse gas (GHG) exchange; however, the interactive effects of climate and herbivory in driving GHG fluxes have been poorly quantified, especially in coastal systems that support large populations of migratory waterfowl. We investigated the magnitude and the climatic and physical controls of GHG exchange within the Yukon-Kuskokwim Delta in western Alaska across four distinct vegetation communities formed by herbivory and local microtopography. Net CO₂ flux was greatest in the ungrazed Carex meadow community (3.97 ± 0.58 [SE] µmol CO₂ m^-2 s^-1), but CH₄ flux was greatest in the grazed community (14.00 ± 6.56 nmol CH₄ m^-2 s^-1). The grazed community is also the only vegetation type where CH₄ was a larger contributor than CO₂ to overall GHG forcing. We found that vegetation community was an important predictor of CO₂ and CH₄ exchange, demonstrating that variation in regional gas exchange is best explained when the effect of grazing, determined by the difference between grazed and ungrazed communities, is included. Further, we identified an interaction between temperature and vegetation community, indicating that grazed regions could experience the greatest increases in CH₄ emissions with warming. These results suggest that future GHG fluxes could be influenced by both climate and by changes in herbivore population dynamics that expand or contract the vegetation community most responsive to future temperature change.