The scale of the problem
The 2000 Biodiversity Strategy recorded that "invasive pests and weeds pose the greatest single threat to biodiversity on land. Weed invasions threaten the long term viability of many of New Zealand's natural habitats."
Russell lupin
Exotic plant species in New Zealand, now number approximately 25,000 species and approximately 2,500 of these are now naturalised (i.e. plants hat have formed self-sustaining populations outside of cultivation). It is estimated that twenty more exotic plant species become naturalised every year.
Why weeds are such a problem
Environmental weeds:
- Transform ecosystems and landscapes, altering the availability of essential commodities such fresh water, e.g. wilding pine.
- Threaten the survival of native plants by smothering or out-competing them, e.g. climbing asparagus.
- Threaten the survival of native animals through providing cover for predators, reducing the availability of preferred foods and by lessening the availability of desirable habitats, e.g. russell lupin.