We plan to use observations, experiments and models to understand how fluctuations in the numbers of small mammal herbivores on the tundra affect ecosystem function (such as the abundance of different types of plants, the quality of plant litter and nutrient cycling). We will conduct experiments in three different Alaska tundra ecosystems (North Slopes, Northern Coast, Eastern Coast) where we will both determine natural changes in small mammal population sizes and also use experiments where we increase or decrease the number of small mammals that have access to areas of the tundra to determine how this affects tundra functioning, and ultimately carbon cycling in arctic ecosystems.