THE DISTRIBUTION AND SPREAD OF ALIEN VASCULAR PLANTS ON PRINCE EDWARD ISLAND

Abstract

Surveys of alien plants at subantarctic Prince Edward Island in 2001 show that the ranges of all three introduced species have increased since the last survey in 1998. Poa annua, the longest-established species, increased its range substantially after 1987, prior to which it was confined to a single site for more than 20 years. It remains largely restricted to sites characterized by intense disturbance by seals and seabirds. Sagina procumbens, the most recently discovered alien plant, has spread even more rapidly (up to 800 m year^-1) and has colonized the west coast of the island (a leap of at least 3 km). Unlike Poa annua, it is not restricted to animal-disturbed areas, although its seeds probably are dispersed by both birds and fur seals. Cerastium fontanum also continues to spread at the island, but remains confined to the western coastal plain, where it occurs mostly on dry feldmark slopes or erosion scars. All three species have expanded their ranges faster than at Marion Island, possibly because of a warmer recent climate and higher densities of seabirds and seals at Prince Edward Island. The ranges of alien plants are likely to continue to expand, with S. procumbens causing considerable changes in the island\'s terrestrial ecology.

Afr. J. mar. Sci. 25: 555–562