Short-term effects of experimental goose grazing and warming differ in three low-Arctic coastal wetland plant communities

Question Understanding the sensitivity and magnitude of plant community responses in tundra wetlands to herbivory and warming is pressing as these ecosystems are increasingly threatened by changes in grazing pressure and higher temperatures. Here, we ask to what extent different low-Arctic coastal wetland plant communities are affected by short-term goose grazing and warming, and whether these communities differ in their responses. Location Yukon-Kuskokwim Delta, Alaska. Methods We conducted an experiment where we simulated goose grazing by clipping the vegetation and summer warming by using open-top chambers in three plant communities along a 6-km coastal-inland gradient. We assessed plant community compositional changes following two years of treatments. Results Grazing had stronger effects than warming on both plant functional group and species composition. Overall, grazing decreased the abundance of grasses and sedges and increased the abundance of forbs, whereas warming only caused a decrease in forb abundance. However, plant communities and functional groups, both within and across communities, varied widely in their responses to treatments. Grazing decreased grass abundance (-25%) and increased forb abundance (+44%) in the two more coastal communities, and reduced sedge abundance (-22%) only in the most inland community. Warming only decreased forb abundance (-18%) in the most coastal community, which overall was the most responsive to treatments. Conclusions We show that short-term goose grazing predominates over short-term summer warming in eliciting compositional changes in three different low-Arctic coastal wetland plant communities. Yet, responses varied among communities and the same functional groups could respond differently across them, highlighting the importance of investigating the effects of biotic and abiotic drivers in different contexts. By showing that tundra wetland plant communities can differ in their immediate sensitivity to goose grazing and, though to a lesser extent, warming, our findings have implications for the functioning of these rapidly changing high-latitude ecosystems.