Invasive animals and plants probably present the largest threat to the remaining ecological values and habitats in New Zealand. A number of animal and pest plants and other invasive species threaten native biodiversity and ecology in Marlborough. The central location and varied climate and landscapes of the region provide a range of habitats and conditions suitable for pests and invasive species.
Pest animals and other invasive species include feral pigs, deer, goats, possums, cats, rats, mice, stoats, ferrets, weasels, hares and rabbits and magpies.
The most obvious invasive pest plants species include banana passionfruit, crack willow, grey willow, Japanese honeysuckle, hieracium, old man's beard, pampas grass, wandering jew, wilding pines, yellow flag iris, and willow-leaved hakea. These are all reasonably widespread in nature, however; no formal obligations exist to control.