An interview with Paul McArthur, Conservation Officer / Protection in the
Nelson / Marlborough Conservancy of the Department of Conservation.
The problems and the planning
The enemies of the birds and bush
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The St Arnaud Range where the mainland island is being developed.
Click here
for a larger version. |
In the earlier articles about Lake Rotoiti I talked about the reduction in
the bird songs around St Arnaud and about Colin Clarke's initiative which
resulted in the removal of 400 wasp nests from the village area. For many
years it has been a major thrust in the policy of the Department of
Conservation Te Papa Atawhai (DOC) to control the wasps, possums, rats,
stoats, weasels and feral cats that are attacking the birds and the bush in
Aotearoa/New Zealand.
DOC's successes in pest eradication
Paul explained that the past successes of DOC have been on offshore
islands. The cats were eradicated from Little Barrier Island and
the possums and rats have been removed from Kapiti Island. DOC's techniques
have been successful in these areas which have not been accessible
to the public.
Mainland islands
These sound like a contradiction in terms, but the name refers to an area
on the mainland, mainly in forests of beech and podocarps, which would be
treated like an island and given intensive pest control programmes.
Five new major mainland island habitats have been established, all
focussed on very different ecosystems. To quote from the DOC pamphlet
"Mainland Islands":
"The potential benefits of mainland islands are enormous for
habitats and their unique ecosystem processes, for the survival
of individual species (flora and fauna) on the mainland and for
New Zealanders in being able to experience first-hand a unique
New Zealand habitat containing a diverse range of native and
endemic flora and fauna."
The Rotoiti Nature Recovery Project differs from the others in that it is
close to the township at St Arnaud and can therefore be visited easily by
conservation-minded visitors from round the world. The project area is
about 800 hectares (about 2000 acres). It is separated from the rest of
the forest on one boundary by the ridgeline of the St Arnaud Range, on
another by farmland and on another by the lake.
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Map by courtesy of the Department of Conservation.
Click here
for a larger version of the map. |
In the mainland island in the Nelson Lakes National Park the focus is to be
on a whole range of pests - wasps, possums, rodents and mustelids (mainly
stoats, but also ferrets and weasels), deer and feral cats. This is a new
concept in the management and conservation of national parks.
The Pests
Possums
Like so many of the pests which DOC is seeking to control or eradicate
possums are not native but were introduced into New Zealand. Traders
wanting to start a fur trade introduced them in 1837. The climate, the
lush vegetation, the absence of predators and the rarity of bush fires all
led to a population explosion. There are now estimated to be over seventy
million possums in the country devouring seven million tonnes of
vegetation each year.
Because they eat the new growth they have destroyed large areas of native
rata, totara, titoki, kowhai and other species. They are eating growth
which previously provided the berries and seeds eaten by the native birds.
They also eat the eggs and chicks reducing bird numbers still further.
They cause dairy and deer farmers anxiety as they are carriers of bovine
tuberculosis.
These are to be controlled by using poison bait stations. which should also
reduce the population of rats.
Rodents
The rats which are a problem in the native forest are mainly the introduced
ship rats which eat small animals, birds' eggs, young birds and many native
fruits and plants.
The first research into the mouse population in the mainland island showed
low numbers of mice. These depend largely on the seeds of the beech tree
for their survival. In the "beech mast" years which occur every three or
four years the trees seed very heavily and there is an explosion in the
mouse population.
Wasps
Again it is the inadvertently introduced wasps which are the main problem.
The native wasps have never become a nuisance. Unfortunately the German and
common wasps have no natural predators in New Zealand and our winters are
not cold enough to kill them.
Particularly in the beech forests they find an abundance of food, feeding
largely on the honeydew on the beech trees. The density of wasps has been
estimated at an average of twelve nests (about 10.000 worker wasps) per
hectare. The biomass of the wasps in the beech forests is therefore
higher than that of all the native birds, plus stoats and rodents.
The wasps are reducing the numbers of native fauna because they eat honey
dew produced on the beech trees by a small sap-sucking insect. This is a
staple food for native birds, bats, insects and lizards. They also eat
insects and on occasion newly- hatched birds.
They are attracted by food and many picnic areas are spoilt by the wasps
which hover round people's picnics. Wasp stings can be very painful. If
you are allergic to them you should carry an antidote with you.
Control of the wasps in the Revive Rotoiti project is to be by using bait
consisting of poisoned cat food. This technique was developed by Landcare
Research. It has been successful on small blocks of beech forest, but in
the Rotoiti project it will be used to cover a large area - 300 hectares
(750 acres).
Landcare researcher Eric Spurr says that there is a good chance that it
will work, as bee keepers have used it successfully in larger areas. It
will knock the wasp numbers back for the season, but will have to be
repeated the next year.
Bait is placed in bait stations on trees at the time when the wasps are
in search of food. They are attracted by the smell and by their need for
protein in their diet.
Mustelids - stoats, ferrets, and weasels
Stoats are the most common of these. They were introduced late in the
nineteenth century by colonists alarmed by the spread of rabbits and hares.
This method of pest control was a disastrous mistake.
They are widespread on farmland and in the forests. They climb trees with
ease and prey on birds, chicks and eggs in their nests.
A labour-intensive programme of trapping will reduce the numbers of stoats
and feral cats. The school children are compiling a register of pet cats
so that any caught in a trap will be able to be returned safely to their
owners.
The hoped-for results
It is hoped that with the pest management birds, plants and insects will
have a chance to survive and thrive in the forests. It is hoped that plant
and animal species such as kiwi and mohua may be re-introduced.
Go to The
Revive Rotoiti Project - Part 2...
