RAPID POPULATION INCREASES IN NATIVE VASCULAR PLANTS IN THE ARGENTINEISLANDS, ANTARCTIC PENINSULA

The number of individual plants and colonies of the two native Antarct ic vascular plants, Colobanthus quitensis and Deschampsia antarctica, have been monitored between 1964 and 1990 on three islands in the Arge ntine Islands archipelago, western Antarctic Peninsula. The Deschampsi a population increased by nearly 25-fold and Colobanthus by over 5-fol d. Furthermore there was a considerable increase in the number of Desc hampsia colonies, although no additional colonies of Colobanthus were recorded. An analysis of Colobanthus plant size in 1974 and 1990 indic ated that recruitment was probably irregular although the population s tructure remained essentially the same. The reasons for this and the i ncreases in population size of both species are discussed. The relativ ely rapid increase in the abundance and distribution of these species is considered to be a response to the increasing summer air temperatur es being experienced in the region of the maritime Antarctic. In parti cular, there is probably improved success in reproductive behavior res ulting from warmer and/or longer growing seasons.