Possums - their introduction & spread
24 Sep 2002
Brushtail possums were among the earliest animals introduced into New Zealand by European settlers.
They were first brought from Australia in 1837 to establish a fur industry. By 1922, 36 batches of possums had been imported, mostly from Tasmania where possums were larger and most had the black fur preferred by furriers. These possums and their descendants were liberated at more than 450 places around New Zealand by 1930.
At the time, these introductions and liberations were considered entirely beneficial, but after 1900 a number of reports of possum damage to crops, orchards, and forests prompted the Government to commission investigations by two of the country's leading botanists, Professor HB Kirk and Dr L Cockayne. They both concluded that damage to New Zealand's forests was negligible.
However, from 1921 to 1947, the Government attempted to stop any further liberation of possums, which was prohibited by the Department of Internal Affairs. Both hunting and selling skins were regulated. The regulations merely provoked a flurry of illegal liberations. During the 1940s, evidence of damage by possums to New Zealand?s forests increased, and in 1947 all restrictions on possum hunting were removed and penalties for releasing them were increased.
The need for action against possums on a national scale was recognised, and in 1951 a bounty of 2/6d (25c) per head was introduced for animals whose skins were not sold. During the following 11 years, more than 8 million bounties were paid, but this did little to control the increasing and expending populations of possums.
In the late 1940s the first survey of possum distribution in New Zealand showed that possums had occupied about half of New Zealand. By 1961-63 they had spread to 84% of the country. Within the last five year Northland and the Coromandel Peninsula have been colonised, leaving few areas yet to be occupied.
The number of possums in New Zealand has been estimated at 70 million, about the same as the number of sheep. Because there are no predators or competitors here in New Zealand, and suitable habitats are readily available, possums occupy most habitats - all types of native and exotic forest, montane scrublands and tussock grasslands; swamps, farmland, orchard and cropping areas; and areas in and around towns and cities. Possums tolerate habitats with a wide range of climates - from arid plans to areas with high rainfall, and from temperate coastlands to harsh alpine slopes at more than 1800m altitude in the North and South Island ranges.
Today possums are considered the major animal pest in New Zealand. In farming areas, they spread bovine tuberculosis to beef and dairy cattle, and to farmed deer, damage crops and orchards, kill poplars and willows planted to control hill-country erosion and stabilise riverbanks, and eat pasture. In exotic forest plantations they kill young trees and stunt the growth of older trees by ring-barking them or breaking the uppermost branches.
In conservation areas, possums cause severe damage by altering habitats important to native animals. Tree species that are palatable to both possums and native birds (e.g. rata, kamahi, and pohutukawa) become much reduced or locally extinct, and are replaced by plants that are less palatable such as tree ferns and pepperwood. As well as altering the composition of native forests and competing with native fauna, possums also prey directly on native insects and birds.
|
