Forage selection by introduced reindeer on South Georgia, and its consequences for the flora.
In 1911 and 1925, reindeer (Rangifer tarandus) were introduced to the subantarctic island of South Georgia where there is a sp.-poor vascular flora and no interspecific competition. Snow cover limited the choice of forage almost exclusively to coastal tussock grass (Poa flabellata) for up to 3 months, and certain forage spp. remained unavailable for up to 6 months. During summer, reindeer selected forage spp. high in N and P, notably Deschampsia antarctica, Acaena magellanica and the alien Poa annua. Native spp. (lichens and A. magellanica) responded quickly and unfavourably to grazing, but tussock grassland was affected only at high population densities. This contrasted with the sequence of overgrazing by introduced herbivores on other subantarctic islands, where tussock grassland was the most susceptible vegetation type. This dependence on tussock grass, rather than lichens, for winter forage was a major reason for the population not having decreased markedly some yr after introduction as has happened at other sites.