Forage selection by introduced reindeer on South Georgia, and its consequences for the flora

(1) In 1911 and 1925 reindeer, Rangifer tarandus L., were introduced to the subantarctic island of South Georgia, where there is a species-poor vascular flora and no interspecific competition. (2) Snow cover limits the choice of forage almost exclusively to coastal tussock grass, Poa flabellata, for up to 3 months, and certain forage species remain unavailable for up to 6 months. (3) During summer reindeer select forage species high in N and P, notably Deschampsia antarctica, Acaena magellanica and the alien Poa annua. (4) Native species (lichens and A. magellanica) responded quickly and unfavourably to grazing, but tussock grassland was affected only at high population densities. (5) This contrasts with the sequence of overgrazing by introduced herbivores on other subantarotic islands, where tussock grassland has been the most susceptible vegetation type. (6) This dependence on tussock grass, rather than lichens, for winter forage is a major reason for the absence of a population crash.