5. Other Invasive Species

Gorse is far from the only introduced species causing problems in New Zealand — it's one part of a much bigger picture. New Zealand's native plants and animals evolved in isolation for millions of years, with no land mammals and few natural defences against the predators and competitors that arrived with human settlement. As a result, the country now carries one of the highest invasive species burdens in the world, estimated to cost the economy in the billions of dollars each year in damage and control efforts combined.

Invasive plants

Gorse shares the landscape with a range of other invasive weeds that compete with and smother native bush. In the Wellington region specifically, Greater Wellington Regional Council manages several under its Regional Pest Management Plan, including:

Wilding conifers

— self-seeding pine species that rapidly colonise open and grazed land, altering water yields and displacing native vegetation across the country.

Old man's beard

— a smothering vine that climbs over trees and shrubs, cutting off light and eventually collapsing the canopy beneath its weight.

Banana passionfruit and blue passionflower

- vigorous climbing vines that blanket native bush margins, particularly in warmer, damper gullies.

Boneseed and climbing spindleberry

— shrubby and vining weeds that establish in coastal and forest-margin habitats, outcompeting native seedlings.

Like gorse, most of these weeds share a common trait: they are far easier to prevent than to remove once established, and control almost always requires sustained, multi-year effort rather than a single treatment.

Invasive animals

New Zealand's invasive animal problem is, if anything, even more severe than its weed problem. Introduced mammalian predators — stoats, rats, and possums in particular — kill an estimated 25 million native birds every year, and are the primary driver behind the national Predator Free 2050 goal to eliminate them entirely. Wellington is aiming to be the world's first predator-free capital city, with projects like Predator Free Wellington and Capital Kiwi already restoring native bird populations to parts of the city.

Other pest animals managed across the Wellington region include:

Possums, rats, and mustelids (stoats, ferrets, and weasels)

— the core targets of Predator Free 2050, managed through site-led control programmes across the region.

Wallabies (Bennett's and dama)

— established in parts of the Wairarapa, and subject to an active exclusion programme to prevent further spread.

Feral goats and deer

— browse native seedlings and accelerate erosion on steep hill country, compounding the terrain challenges gorse control already faces.

Wasps and rabbits

— significant pests in their own right, with wasps in particular disrupting native insect and bird food sources in beech forest.

Why the Trust's focus is gorse

With so many introduced species affecting the region, no single organisation can tackle all of them — which is exactly why New Zealand's pest management relies on a network of specialist groups working alongside councils and the Department of Conservation, each focused where they can add the most value. The Wellington Region Hills Environmental Trust exists to solve one specific, high-impact piece of that wider puzzle: gorse control on the steep, hard-to-reach hill terrain that conventional methods have never been able to treat effectively. Progress on gorse also supports the region's wider restoration efforts — clearing gorse and re-establishing native cover creates habitat that complements predator-free initiatives working to bring native birds back to Wellington's hills.