Pest animals such as possums, goats, deer, wallabies, rabbits, ferrets, stoats and weasels can inhabit forests, bush and dune lands and either directly damage trees or under storey plants, change forest composition, or prey on indigenous fauna.
Animals that can directly damage trees include possums, deer, goats, wallabies and rabbits. Possums are principally arboreal herbivores, eating leaves, flowers and fruit. Their browsing behaviours seriously damages indigenous vegetation, but they also feed on pine, eucalyptus and wattles and other timber trees at certain times of the year. Possums also eat or destroy both eggs and chicks of native birds and compete with native species for a wide range of native food sources. Possums can also act as vectors for bovine tuberculosis, which they can then pass to cattle and other farm stock.
Deer damage young pine stands by feeding on the terminal shoots of recently planted pine seedlings. Young trees are also often damaged when antlered bucks use them as scraping posts. Deer will also destroy the under storey of native forest by over-browsing, grazing, bark stripping and trampling. Feral deer can also act as vectors of bovine tuberculosis.
Goats are one of the most destructive animals found in forests. They will browse on a very wide range of plants in the under storey, and up to about two metres above ground. As well as damaging native forests, they also damage newly planted or young trees in exotic forests.
Wallabies are not widespread and found only in a few areas of New Zealand . They eat grasses, native trees and scrub, and live mainly in the margins of scrub and coastal forest, where their browsing of native plants changes the vegetation so that eventually the area cannot support native birds.
Rabbits can damage plantation and forestry tree seedlings, especially during late winter and early spring, when they need the roughage and sugar. Bark and foliage is bitten or chewed, roots are dug up, and seedlings are sometimes nipped cleanly in half.
The ferret, stoat and weasel belong to a group of mammals known as mustelids. They do not directly damage our forests but instead prey on native birds, bats, lizards, frogs, insects and snails which are found in both farmland and forested areas. Mustelids especially ferrets play a suspected participation in the bovine tuberculosis cycle. They can also carry parasites and toxoplasmosis, which cause abortions in sheep and illness in humans.
Control methods available for the larger animal pests such as deer, goats and wallabies include shooting, exclusion fencing and poisoning. For the smaller animal pests such as possums, rabbits and mustelids shooting, poisoning and trapping are the main methods. Repellents can also be applied to the trunks and leaves of trees or seedlings to deter rabbits and other animals from feeding on them.