In its native land the possum is up against dingoes, bush fires and less palatable vegetation, but in New Zealand conditions are so favourable it often breeds twice in one year. It is estimated that the New Zealand possum population now tops 70 million and chomps its way through seven million tonnes of vegetation per year. The damage to native forests can be seen all too clearly in many areas. Possums ignore old leaves and select the best new growth. In some areas they have eaten whole canopies of rata, totara, titoki, kowhai and kohekohe.
Possums compete with native birds for habitat and for food such as insects and berries.
They also disturb nesting birds, eat their eggs and chicks and may impact on native land snails. Dairy and deer farmers have the added worry of possums spreading bovine tuberculosis. Possums are a nuisance in suburban gardens, and sometimes even indoors. Individual trees can be protected with metal strips placed about a metre above ground level, as seen on telephone poles, to stop possums from climbing up. Allow to set, then spread on the base of the tree.