Heterogeneous Impacts of Grazing Animals and Vegetational Change in Japanese Native Pastures

Defoliation, defecation and trampling are the major modes whereby grazing animals give impacts on vegetation. Due to the uneven distribution, such grazing behavior can have profound effects on vegetation. For extensive grazing systems in native pastures, understandings of the plant-animal interaction are vital for adequate control of vegetation and animal conditions and sustainable use of natural resources. This paper reviews recent studies of the grazing impacts on vegetation in Japanese native pastures. Most of the studies were carried out in the Kawatabi Field Science Center (Kawatabi FSC), Tohoku University. 1.Native pastures in the Kawatabi FSC are composed of 61-155 plant species, of which cattle graze upon 26-76 species. Among these species, Miscanthus sinensis (Japanese plume-grass) was the most frequently grazed by cattle. The spatial distribution of available forage is a major factor affecting diet selection and consumption of cattle. Such selective grazing results in significant reduction of M. sinensis in native pastures. 2.Seed dispersal of plants by defecation of grazing animals can also result in significant vegetational change. Recent studies have shown that Carex spp. is the major plant whose seeds are dispersed by defecation of animals rotationally grazed in a native and a sown pasture. The mechanisms of the seed dispersal and its possible effects on vegetational succession are discussed. 3.Heavy trampling is known to degrade vegetative ground cover. Our research has shown that trampling by cattle promotes the invasion of a shrub, Weigela hortensis into Miscanthus-dominant pastures. Because the seeds of W. hortensis are light sensitive germinators, trampling by removing ground cover promotes its seed germination. These findings provide new perspectives on plantanimal interactions in Japanese native pastures and help estimate the impact of animals on plant succession. They also contribute to efforts to ensure sustainable grazing use of pastures