Effect of sheep grazing and fertilization on species richness, diversity, and biomass in an alpine area in Central Norway

Abstract

Impact of herbivores in different ecosystems is an important subject in ecology. Herbivores have been shown to have a large and complex impacts on ecosystems around the world that can drive changes of plant community structures though different mechanisms. Most studies looking at how herbivores affect plant communities in alpine ecosystems have been performed in enclosure studies, and over shorter periods of time. In this thesis, I investigated how free ranging sheep (Ovis aries) affect alpine plant communities over 15 years in two study sites in Forrolhogna National park Central Norway. I analysed eight 50 x 50 m plots. Four plots had been fertilized in the beginning of the project in 2003, and then each year until 2006, while the other four had no treatment done to them. All plots were available for grazers. I counted sheep pellets groups inside plots to see how sheep distributed themselves inside plots. The aim of this study was to see whether species richness, -diversity and functional plant group cover changed in control plots and fertilized plots over 15 years and if these changes contributed to more nutritious plants that increased grazing from sheep. Species richness and diversity increased in control and fertilized plots, while cover of graminoids decreased in both control and fertilized plots. Sheep showed no selection for fertilized plots over control plots. The grazing pressure in the study area are relatively low and the results of my study suggest that other factors such as temperature and precipitation might have a greater impact on the vegetation than fertilization and grazing.

This study emphasizes the importance of long-term studies for understanding how vegetation processes respond to fertilization and how this affects grazing pattern for herbivore in the long run.