Why are introduced animals a problem?

An introduced wild animal

New Zealand's long history of evolutionary isolation has meant that New Zealand's fauna and flora is particularly vulnerable to the damaging effects of introduced animals and plants.

The browsing and grazing of animals such as possums, goats, pigs and deer has severely impoverished large areas of indigenous forest, contributed to the extinction of several species of flowering plants, and endangered many others. If left unchecked, introduced animals will continue to degrade our forests, causing a continuing decline in biodiversity. In those areas where browsing animals stop regeneration, the result will be the complete collapse of the forest canopy.

Department of Conservation's role

The main function of the Department of Conservation is the protection of New Zealand's unique native plant and animal communities. Many people do not realise, however, how much of this work focuses on the control of introduced animals and why.

Why do we need wild animal control plans?

Experience in New Zealand and elsewhere has shown that, to be effective, animal pest control must be co-ordinated and focused, with clearly stated goals and objectives, methods for achieving objectives, and provisions for monitoring whether objectives are being met. This requires a high level of organisation and planning.
For example, the eradication of possums throughout the whole of New Zealand is not possible with present resources and technology. Therefore, in order to address the possum problem, the department must determine which forests are at risk of canopy collapse and loss of biodiversity and prioritise resources to provide the greatest benefit for conservation.

The legislation

Section 5 of the Wild Animal Control Act 1977 gives the Department the authority to prepare wild animal control plans, outlining the strategic approach necessary for the effective control of introduced animals.

What do the plans contain?

Wild animal control plans outline the problems caused by introduced animals; state the Department's policies; set goals and objectives; and assess and justify the need for and means of control. Wild animal control plans also provide criteria for the identification of native plants, animals and natural communities most threatened by introduced animals, and enable managers to establish where, when and how much control should be carried out.

Using the strategic planning framework provided by these plans, resource allocation decisions can be made in an open and transparent way. Wild animal control plans also outline how operational and performance monitoring must be carried out so that animal control operations can be monitored to ensure that they are effective and that there is an improvement in forest health.

How are the plans developed?

People attach a range of different values to wild animals. Some agree that wild animals are significant conservation pests, while others, however, see wild animals such as deer, pigs and goats as an important recreational and commercial resource. Wild animal control plans are developed in consultation with user groups and stakeholders. Within the constraints set by legislation, the department attempts to accommodate the interests of user groups while achieving conservation objectives. The aim of involving interest groups during the preparation of plans is to avoid future conflict and expensive litigation.

What wild animal control plans has the Department prepared?

The Department has prepared and implemented wild animal control plans for thar and possums. A National Feral Goat Control Plan is also near to completion. The process for preparing a national deer control plan has begun and the proposed format will shortly be reviewed by an overview group which will include hunters and conservation non-governmental organisations.

The department has also developed a Kaimanawa Wild Horses Plan and a National Wasp Control Plan under the Wildlife Act 1953.

What have these plans achieved?

The Department carries out possum control over 1.4 million hectares of land and controls goats over almost 1 million hectares. Where control work has been carried out under wild animal control plans, the results have often been spectacular.

For example, Melicytus "Egmont" is a species of divaricating mahoe that occurs only in the Ahukawakawa swamp and on the Pouakai Range in Egmont National Park. Before possum control 3 years ago, all these mahoe plants had closely cropped canopies and there was no regeneration. Now, many plants have canopies with elongated shoots and stem bases have numerous shoots. Seedlings have also established, boding well for the future of this plant.

Future challenges and opportunities

The Department is not the only organisation involved in control of wild animal pests. The Animal Health Board controls possums and feral deer to prevent the spread of Tb to cattle. Regional councils and community groups control possums to enhance agricultural production.

The Department, along with these other agencies participates on the national possum co-ordinating committee, which is continually looking for opportunities to co-ordinate control and research where this is possible.
The challenge facing the department is to integrate the control of a wide range of animal and weed pests with its threatened species work to achieve the best possible biodiversity conservation outcomes.

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