New Zealand’s Mainland Islands Fencing Out Non-Native Predators

Islands often serve an important role in protecting and preserving species because of their isolation and lack of predators. But some species aren’t suited to the offshore ecosystem, and some countries don’t have the islands to devote to conservation efforts. New Zealand has decided to import the benefits of offshore island habitats inland by creating “mainland islands,” typically surrounded by large predator-resistant fences. Despite early success, the effort is meeting some scepticism and resistance.

Pest-proof fences like this one make it possible for New Zealand to restore native flora and fauna in specially created “mainland islands.”©The Xcluder— Pest Proof Fencing Company

New Zealand’s history of introduced pests (especially man) has had a devastating impact on biodiversity. Many native species are now extinct, and the fight to conserve what’s left has the country’s Department of Conservation (DOC) scrambling for strategies. These range from trapping and poisoning exotic pests to shifting the entire population of an endangered species (such as the flightless kakapo parrots) to offshore islands that have been cleared of predators.

But conservation programs aimed at specific ecosystems such as fertile lowland plains, terraces and swamps can only be undertaken at mainland sites. These artificial mainland islands can be created by means of fencing, accidental geographical features or by intensive management. As designs have improved and costs have come down, the erection of pest-proof fences around large tracts of land is becoming increasingly affordable and popular as an efficient way to exclude predators such as rats, weasels, stoats, ferrets, possums and feral cats.

The land-locked islands typically get started as a local environmental group’s vision, which is then embraced by landowners, farmers, local councils and the general public. An early example is Karori Sanctuary in Wellington on 622 acres of native forest started in the 1990s. The area was a water reservoir catchment that was closed to the public for 120 years.

Karori Sanctuary has a long-term restoration strategy for forests, wetlands and wildlife. It takes 500 years for native trees like New Zealand’s rata, rimu and totara to get established, but in the first 10 years, birds such as little spotted kiwi (the national bird), brown teal, bellbird, native robin, scaup, weka and pigeon, as well as reptiles like the rare tuatara lizard, have been reintroduced.

The latest mainland island planned is near Nelson on the South Island, named the Brook Waimarama Sanctuary. A pest-proof fence will encircle 1,700 acres of a former water reserve. Eradication of all the pests inside the fence will create a sanctuary for the eventual re-introduction of the full range of lost species. The Brook Waimarama Sanctuary Trust (BWST) plans to raise the $2.1 million for the fence by 2008.

“Imagine a place where native plants and animals thrive without introduced pests,” says Dave Butler, BWST chairman. “We”ll be able to re-introduce rare species in the sanctuary, and local school groups will be able to study native forest ecology.”

New Zealand’s endangered kiwi.©The Xcluder— Pest Proof Fencing Company

Effective pest-proof fences must be windproof and waterproof, but allow water to pass under the fence through pest-proofed culverts or stream crossings. To construct a completely pest-proof fence (that keeps out mice), it must be built with no gap bigger than two-tenths of an inch. Mouse eradication attempts have had mixed success over the years—the Karori Wildlife Sanctuary was actually re-invaded by mice. But fence design is constantly improving and pioneer companies such as Xcluder are now testing fences in Mauritius, Australia and Hawaii.

Not all mainland islands depend on fences. At Lake Rotoiti Nature Recovery Project in Nelson Lakes National Park, 12,000 acres of beech forest will be restored through an extensive predator trapping program. The park will eventually host native species like kaka, kakariki, bush robins, mistletoe, giant snails, lizards, bats and insects.

“Trapping is the key management tool for Lake Rotoiti,” says Brian Paton, DOC biodiversity program manager, adding the program cost is just $136,000 a year. “Fencing 12,000 acres of land would be a logistical and budgetary nightmare just to patrol it, never mind the cost of buying and installing it. We are seeing good increases in native bird life in our restoration area.”

The success of this mainland island is attracting more than 100,000 visitors a year to Lake Rotoiti. The recovery area is right beside a campground so the public can readily experience native flora and fauna.

Elaine Wright, DOC terrestrial sites manager, is non-committal on the future of fenced mainland islands: “Fences are one of the sweetest techniques we can use, but they’re still just one tool in the toolbox, and not appropriate for highly mobile species such as falcons.”

Wright explains that the DOC is directly involved in only six of the country’s 70 mainland islands, including Rotoiti, but supports the other projects as much as resources will allow. “The islands we manage tend to have specific learning objectives and are often more experimental than community-driven islands,” she adds.

“I have no problem with the concept,” says Owen McShane, director of New Zealand’s Centre for Resource Management Studies. “But why do these projects have to be on such a large scale and controlled by DOC? Private landowners know a lot about pest control too. DOC is desperately short of manpower, so why not let the private sector help out?”

McShane suspects a hidden agenda behind the growth in mainland islands. “DOC already controls 40 percent of New Zealand’s landmass. I suspect these mainland islands may be another way of locking people out of areas that could be used for recreational or economically productive purposes.”

McShane’s views seem to be in the minority, since mainland islands are attracting widespread public support through time and money donations. The recent creation of a national group called Sanctuaries of New Zealand reflects the growing number of people who see the benefits. Not the least of these, say supporters, is the fact that mainland islands not only allow the reintroduction and protection of plant and wildlife, they also become education and tourism resources that enhance local employment opportunities.