Two Arctic graminoids growing with increased soil nutrients recover differently from mammalian herbivory

In the Arctic, higher air and soil temperatures associated with global warming increase the availability of nutrients for plants often altering plant species composition, diversity and productivity. While mammalian herbivores in arctic tundra have been thought to be of low importance to plant communities because of low abundance, their effect on plants when nutrient availability is greater and plant productivity is higher has not been well studied. To examine this, I used long-term experimental plots established in 1996 that add soil nutrients and exclude mammalian herbivores, particularly voles, in two arctic Alaskan plant communities. For one species in each community, I compared growth among three treatments: natural levels of mammalian herbivory, simulated (manual clipping) herbivory, and exclusion of mammals. When soil nutrients were more available, mammalian herbivores and clipping decreased the growth of Eriophorum vaginatum in moist acidic tundra relative to plants protected from mammals. However, Hierochloe alpina in fertilized dry heath tundra grew following clipping and herbivore damage so that after three years no differences in leaf length were present among treatments. Thus, as arctic temperatures continue to increase and nutrients become more available to arctic plants, the response of plants to mammalian herbivores may vary among species depending on community context and species specific resilience to biomass removal. Further, because mammalian herbivore abundance may increase in the Arctic because of higher plant productivity due to increased temperatures, animals should be considered more important in shaping a variety of plant communities than they are currently.