In its native land (Australia) the possum is up against dingoes, bush fires and less palatable vegetation. In New Zealand there are no predators and lots of very palatable vegetation. As a result possums have a huge impact on New Zealand ecosystems.
Possums (Trichosurus vulpecula, Trichosurus = bushy tailed, Vulpecula = fox like) were first introduced to Riverton, Southland in 1837 to form the basis for a New Zealand fur industry. This initial attempt failed, but 36 importations and releases mostly by Acclimatization Societies between 1858 and 1921 saw possum numbers quickly multiply. In 1946, possums were declared a noxious pest.
Population estimates and future
Based on modelling work carried out by Landcare Research, including extensive control measures by TB-free NZ, regional councils and the Department of Conservation, it is estimated there are about 30 million possums in the country today.
A popularly quoted figure of 70 million possums has been calculated on the basis if no control measures were carried out.
Possums eat the forest at every point, including leaves, buds, flowers, fruit and seeds from the tallest trees. On the ground they eat seedlings, saplings and sometimes bark, and favoured foods include Mistletoes (some driven almost to extinction), tree Fuchsias, Kamahi and Rata trees.
It has been estimated that up to 21,000 tonnes of vegetation a night is destroyed by possums. As well as competing for food with native insects, bats, and birds, they also eat them and their eggs and nestlings. Possums also drive native animals out of their dens and nesting sites.