Exotic plants on Lord Howe Island: distribution in space and time, 1853-1981.

Some 173 exotic angiosperms form 48.2% of the angiosperm flora of Lord Howe Island, South Pacific Ocean. The families Poaceae (23%) and Asteraceae (13%) dominate the exotic flora. Some 30% are native to the Old World, 26% from the New World and 14% from Eurasia. Exotics primarily occur on heavily disturbed areas but c10% are widely distributed in undisturbed vegetation. Analysis of historical records, 11 species lists over the 128 years 1853-1981, shows that invasion has been a continuous process at an exponential rate. Exotics have been naturalized at the overall rate of 1.3 species yr^-1. Most exotics were deliberately introduced as pasture species or accidentally as contaminants, although ornamental plants are increasing. Exotics show some evidence of invading progressively less disturbed habitats but the response to each species is individualistic.-from Author