The Ministry for the Environment is currently coordinating the development of environmental performance indicators for pests, weeds and diseases. A discussion document including proposed indicators will be released for public comment in 2001. Some, like sheep and pine trees, were introduced intentionally and have had economic benefit but most arrived by accident and caused varying degrees of damage. Weeds are generally exotic garden plants gone wild.
Pests pose a threat to New Zealand's native plants and animals and their homes.
By preying on existing species, competing for space and food, and damaging habitats these invaders can seriously affect native biodiversity. Possums are a serious threat to biodiversity. There are numerous invasive weeds and diseases that are just as problematic. Unwanted pests and weeds cost the country in other ways as well. Agricultural and horticultural productivity suffers when crops, flocks, herds and harvests are blighted by pests or diseases.