Effects of biomass and quality of forage on grazing by breeding and spring staging barnacle geese (Branta leucopsis): Field observations and experiment on Gotland

Barnacle geese (Branta leucopsis) are strongly dependent on the quality and availability of forage plants to compensate for limiting digestive capabilities. In spring geese are migrating from temperate wintering grounds to high Arctic breeding grounds following a 'green wave' of spring growth. On three different stepping stones along the East Atlantic Flyway (Schiermonnikoog, Gotland, Pechora Delta) we carried out an experiment where we manipulated biomass -and quality of forage to investigate the relative importance of these factors for grazing pressure and to study whether the relative importance changed along the flyway and over the season. This report describes the results for Gotland, a spring staging site for the Arctic and a breeding site for the Baltic population. On Gotland we also studied food availability, I food quality and grazing pressure in four intensively goose grazed areas to get a general idea of changes of these parameters over the season. Grazing pressure was strongly increased on experimental plots that were both biomass and quality enhanced. In the natural situation habitats with high quality and low biomass were more intensively grazed than areas with low quality and high biomass, which indicates that quality is an important factor determining goose presence. These results correspond with results from earlier research showing that in a natural situation there was a negative relationship between sward height and grazing pressure, due to the negative correlation between sward height and nitrogen content. When this relation was eliminated by application of fertiliser a higher preference for longer swards was shown (Hassall et al. 2001; Riddington et al. 1997).