Pests & weeds

National Parks are areas to be kept in as natural a state as possible. They have become havens, or strong-holds, for our native flora and fauna; remnants of a former New Zealand . Unfortunately these havens are now isolated like islands, constantly under threat of invasion from introduced plants and animals.

Seed from introduced plants are blown into the area, carried in on people's clothing, in vehicles or on boots. Some times it is carried in by animals. In some of the worse cases, it was introduced on purpose by people in our early history. Introduced animals find their way in from neighbouring areas, or like the plants were once introduced.

These plants and animals threaten to change the whole nature of Tongariro National Park . This area is unique in its tussockland and alpine herb fields. Many introduced plants are able to grow much more vigorously than our native species, and at a much higher altitude; smothering and pushing out the natives. Introduced animals prune back and kill many of the native plants by browsing. Others may prey on and kill native birds and insects.

Some of the problem invaders include:

Lodge-pole Pine (Pinus contorta)

Pinus contorta in Tongariro National
Park being removed

Originally planted around the boundaries of the park as an experimental forestry crop, these pines have spread all over the desert, tussock and alpine country. They will grow high up on Mt. Tongariro and on the skifields of Mt. Ruapehu. It was recognised that the problem would never be wholly eliminated from the area until all the seed producing trees were removed.

All the major landowners and managers (district councils, military, Department of Conservation, and iwi groups), have agreed to remove all their seed bearing trees from the surrounding land. Once removed it will only require regular eradication of wildling seedlings to finally put an end to this problem species. A Pinus contorta control programme is run on a yearly basis by the department.

Heather (Calluna vulgaris)

Heather now covers much of the
western side of Tongariro National Park

Originally planted by one of the early park wardens around 1910, heather was introduced to the area as a food source for pheasant and grouse which were to be introduced to Tongariro National Park as gamebirds. Public outrage stopped their introduction in the park, although they were released in neighbouring areas. The birds did not survive the harsh climatic conditions of the Tongariro area, but unfortunately the heather did. It has spread throughout the tussock country, smothering and pushing out the red tussock.

Heather is difficult to control. It is expensive to do so, and the plant is so successful in this area that most control methods are inadequate. Pulling out the plants generally loosens the soil and releases lots of other seeds, ensuring that heather is usually the first thing to grow back. If you spray heather, large areas of vegetation are killed, including desirable native species.

At present a form of biological control is being attempted in the form of the heather beetle (Lochmaea suturalis). This beetle is from Scotland and feeds only on heather. To be sure of this, there have to be many tests and trials to ensure that the beetle will not feed on any of our native plants. In 1996, the heather beetle was released on two sites in Tongariro National Park . It will not get rid of the heather all together, but hopefully it will slow its spread and allow the native species to regenerate with less competition.

Broom (Cytisus scoparius)

Broom is found in patches throughout
the park

Broom is a dark green plant with bright yellow flowers, similar to gorse flowers. It is too widespread throughout New Zealand to ever be able to eradicate it completely. Here in Tongariro National Park, it threatens every view of the area, and smother the native plants. The department has a broom control programme which runs on a yearly basis.

Patches of broom are spread throughout the park; many a long way from road or foot access. The most effective way to reach all these plants is to move teams of people from plant cluster to plant cluster by helicopter. Broom stands out against the brown-green of the native plants; even when not in bright yellow bloom. It is cut down and the stumps are sprayed with a 'non hormonal' weed killer so neighbouring natives are not destroyed.

A broom insect has been released in Tongariro National Park . It feeds only on the seeds of the broom bush, and it is hoped that as it spreads in the area, it will slow the spread of the broom. Like the heather beetle, it was tested extensively before it was finally released.

There are many other weeds that threaten the park. Lotus major comes in with road metal. Thistles are brought in on trampers socks and spread by animals. Old Man's Beard spreads over the forest smothering the tree tops. The list is never ending, there are always new threats to the plants of the park.

Deer

Deer were released in the park early this century for the sport of hunting. Unchecked they can cause significant browse damage in the forests. For this reason hunting is permitted in the national park. Hunters must get a permit and these are issued at no cost. In return we ask hunters to complete and return a diary of how many animals they shoot and if possible, to leave a jaw sample. This enables the department to monitor the deer population in a particular area and determine the age and health of the animals.

Possums

Possum caught in Timms humane trap

Introduced for their fur, the possum has spread throughout the country. They are responsible for the decline and deterioration of many of our native plants and trees including pohutukawa, mistletoe and kamahi. They are also responsible for the spread of diseases such as tuberculosis and giardia.

The problem is immense. Poisons and traps are laid to try and reduce their numbers, but the vast area of Tongariro National Park and nearby forests together with difficult access in places; make control programmes costly and time consuming. It is possible for hunters to get 'possum blocks'. These are areas designated for hunting possums for the skins. However, the price for fur is so low at present that few people take up the offer.

Goats and pigs

Although the numbers of goats and pig are not high within Tongariro National Park , they are found in other reserves and parks in the area. The department endeavours to keep the numbers down by regular hunting. Recreational hunting is also encouraged, and in some cases, professional hunters are employed. Particularly if animal numbers are high or there are insufficient staff are available.

There are many other animal pests found within Tongariro National Park . Many are so widespread throughout New Zealand , and so mobile, that there is little we can do except control their numbers locally. These animals include: hares and rabbits; stoats, ferrets and weasels; rats and mice; and cats.

It is sad, but new Zealanders are now more familiar with a blackbird, sparrow or magpie than they are with a robin, rifleman or kokako. Pine trees, gorse and broom are now an everyday sight. If we want to preserve any of our unique New Zealand plants and animals, then we must protect what we have left before it is completely gone. We need to respect conservation areas; try not to introduce seed and foreign plants and leave our household pets at home, when we are visiting these places; and look after the fences around these areas that keep out animals. If we all take a little care, we will be able to enjoy our national parks and special native flora and fauna for all time.

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