Pests and weeds

Effects on the native flora and fauna

National parks are precious areas of our natural landscape, to be kept in as natural a state as possible. They are havens for our native flora and fauna; remnants of a former New Zealand. It is unfortunate that these havens are 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, or 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 pest plants and animals threaten to change the whole nature of Tongariro National Park. The tussockland and alpine herb fields of the area are unique. 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.

Common pests and weeds

Some of the problem invaders include:

Pinus contorta being removed, Tongariro National Park. Photo: Harry Keys.
Pinus contorta being removed

Lodge-pole pine (Pinus contorta)

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

Measures to control lodge-pole pine

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 covers much of the western side of the national park. Photo: DOC.
Heather now covers much of the
western side of Tongariro National Park

Heather (Calluna vulgaris)

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 the birds' 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 spread throughout the tussock country, smothering and pushing out the red tussock.

Measures to control heather

Heather is difficult and expensive to control. 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 is found in patches throughout the park. Photo: DOC.
Broom is found in patches throughout
the park

Broom (Cytisus scoparius)

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 smothers the native plants. The department has a broom control program which runs on a yearly basis.

Measures to control broom

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 was 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 in the early 1900s 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 require a permit, available free online. Hunters can choose to 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.

Possum caught in Timms humane trap. Photo: Jimmy Johnson.
Possum caught in Timms humane trap

Possums

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

Measures to control possums

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 programs costly and time consuming. It is possible for hunters to get 'possum blocks'. These are areas designated for hunting possums for the skins.

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.

Other pests

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.

What you can do to help

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 and enjoy 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 protected 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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Phone:      +64 7 892 3729
Address:   Whakapapa Village
State Highway 48
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Email:   tongarirovc@doc.govt.nz
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