Climate change is altering plant species assemblages throughout the Arctic, which may have consequences for herbivore resource availability. Migratory geese that spend their summers in coastal Arctic wetlands are experiencing changes in population densities and are shifting their distributions into novel habitats (i.e., further inland) as flooding and sea-level rise increase. Further, warming temperatures alter plant community assemblages, often by increasing woody species in these graminoid-dominant systems. Previous studies conducted in the Arctic have found opposing effects of grazing and warming on plant community composition; however, how these forces influence coastal vegetation and how they interact are less understood. We investigated the impacts of changing herbivory patterns and warming on three plant communities in the Yukon-Kuskokwim Delta in western Alaska, ranging from the coast to 6 km inland and asked: How do herbivory, warming and their interaction affect vegetation biomass, community composition, and plant functional groups? To address this question, we conducted a two-year full-factorial replicated experiment where we simulated goose herbivory and warming in these three plant communities.
Results/Conclusions
By the end of the second year of the experiment, we found that grazing had the strongest effect on the most coastal communities, decreasing grass (Festuca rubra, Leymus mollis, Poa eminens) and sedge (Carex ramenskii, C. rariflora) cover and increasing forb cover (Argentina egedei, Chrysanthemum arcticum, Stellaria humifusa, Triglochin palustris). In contrast, warming had the strongest effect on the most inland community, resulting in reduced forb (C. arcticum) and increased shrub (Salix fuscenscens) biomass. Despite the observed effects of both warming and herbivory, we found no interaction effects between these impacts in any of the communities. While grazing reduced the cover of dominant goose forage, Carex species, in the most coastal communities increases in secondary forage species, such as A. egedei and T. palustris, appeared to offset the reduction in forage availability. Our findings suggest that if geese alter their distribution and begin grazing further inland, this could shift the plant community composition from graminoid- to shrub/forb-dominated, resulting in the potential decoupling of herbivores and their forage species in a critically important coastal ecosystem.