Some Effects of Mammalian Herbivores and Fertilization on Tundra Soils and Vegetation

Abstract

Elevated concentrations of soil nutrients, particularly nitrogen and phosphorus, are associated with activities of mammalian herbivores. The sources of these nutrients appear to be waste products or carcasses of the herbivores themselves. Vegetation appears to respond to higher than normal concentrations of soil nutrients by increased importance of graminoids, decreased importance of lichens and, sometimes, decreased importance of shrubs. Plants growing within areas of elevated soil nutrients tend to have higher nutrient concentrations in their tissue. Artificial fertilization with nitrogen and phosphorus produces similar effects and support these interpretations. We conclude that nutrient transport by herbivores has significant local effects on soil nutrient concentrations and, therefore, on the composition of the vegetation. Measurement of fecal production and soil turnover by burrowing indicate that it may take many years (perhaps hundreds) for the cumulative effect of herbivore activities to be noticeable. Direct effects on vegetation by microtine rodents could not be detected 1 yr after grazing, but long-term studies might produce different results.