FIGURE 3.

Herbivore effects on element cycling in arctic tundra ecosystems. Gray lines show nutrient flow between plants, soil organic matter, and soil nutrients in the absence of herbivores, and black lines show how herbivores affect nutrient pools in each of these compartments. Solid and dashed lines are indicative of nutrient (N, P) and carbon flow, respectively. Consumptive effects in (A) are due to direct consumption of plant matter. Nonconsumptive effects in (B) include physical disturbance that modifies soil structure through trampling (Rangifer, muskox, and geese), building hay piles (voles), or grubbing (geese). Changes in plant quality (shown in panel B) due to direct and indirect effects of herbivore activity include changes in plant functional traits, plant nutrient content or stoichiometry, and plant community composition (see text for detail).