Problems in pest control: the lessons of Pitt and Chatham islands

The Chatham Islands pose a number of unique and complex problems in wild animal control. Possums, pigs, feral and domestic sheep, cats, rats, wekas and above all, people, threaten the rare and unique plants and animals.

The climate is severe with strong winds, frequent fogs and low rainfall. Although small, the islands contain a very diverse geology including limestones, schists and volcanic rocks, all of which affect plant distributions.

The fragmented nature of the remaining forest stands means that determining former vegetation pattern is difficult. This problem is further compounded by the severe browsing and its prolonged impact in the majority of stands. Destruction of shrubby vegetation upwind of tall stands by introduced animals leads to windblast damage to the remaining stand and the inevitable decline of the whole forest.

Control of domestic stock is gradually being achieved but removal of wild sheep presents problems in timing. There are also problems because of the genetic value of the resource.

Recovery of the vegetative cover is often rapid but return of the former predominant communities will be slow. In a few areas replantings will be used to assist the return of native fauna and flora. In some areas maintenance of a low level of browsing may be necessary to achieve other project objectives.