Invasive plant problems and requirements for weed risk assessment in the Galapagos Islands

Galapagos is a young oceanic archipelago with a native vascular flora of 560 species, few native trees, and an absence of many families present on the neighbouring mainland. It has only recently become subject to human influence. Plants introduced by man have only become problematic in the last 150 years, with most weed problems being less than 50 years old. The rise in plant introductions parallels the human population increase, with a recent introduction rate of 10 plant species per year, 100,000 times the natural colonization rate. Invasive plants include weeds and cultivated species, which cause detrimental effects on agriculture as well as natural habitats. Introduced species are the principal threat to the Galapagos ecosystem, and several species of alien plant are seriously damaging native habitats and threatening endemic species. Examples of some of the worst invaders and of the process and effects of invasions are presented. A weed risk assessment system for Galapagos must take account of the particular requirements of a fragile oceanic island ecosystem and flora. It must include consideration of potential invaders as well as plants already introduced. Factors that need to be included in an objective risk assessment system for Galapagos are discussed in light of the New Zealand Department of Conservation’s model