Livestock grazing modifies the effect of environmental factors on soil temperature and water content in a temperate grassland

Abstract

Grazing by large herbivores modulates the soil temperature and the water content as well as the quality of resources returned to the soil. Therefore, in order to predict the effects of grazing on complex interacting soil processes and plant production, an integrated approach is needed. We hypothesized that grazing accelerates nutrient cycling by increasing (i) soil temperature and fluctuations, (ii) water-holding capacity, and (iii) forage quality. To test this biological hypothesis, we conducted a field experiment simulating grazing abandonment conditions in semi-natural mountain grassland plots. Our results show that grazing accelerates soil processes through all three hypothesized mechanisms. Since grazing maintains a thin organic layer that provides less insulation to the soil, higher mean temperatures and large daily temperature fluctuations were recorded in grazed areas (less insulated); these daily fluctuations were as large as seasonal variation in the ungrazed plots. The response of the soil water content to grazing was complex. Although overall exclusion reduced the soil water content, particularly in coarse-textured soils, this trend was reversed during long periods of high solar radiation (i.e. high evaporation). Forage quality was reduced in all plots when grazers were excluded. Experiments attempting to realistically simulate grazing may benefit from these findings, particularly in very productive grasslands where the thickness of the organic layer increases rapidly under grazing exclusion.