Wallabies a major threat to indigenous forests

The Dama wallaby is considered a pest in New Zealand. Photo / Martin Skyes

A cousin of the kangaroo could wreak havoc if it spreads through the Kaimai and Urewera ranges, conservationists fear.

The Lakes Water Quality Society, a collaborative organisation that aims to restore the health of lakes in the Rotorua region, has chosen the troublesome dama wallaby as a theme of its annual symposium to be held in Rotorua on March 12 and 13.

While endangered in South Australia, the species is considered a pest in New Zealand.

According to the most recent distribution survey, it had spread throughout nearly 170,000ha of the central Bay of Plenty.

The first wallabies to reach New Zealand were released on Kawau Island around 1870 by Sir George Grey, before a population was released in the Rotorua district just over a century ago.

The species preferred a habitat of relatively dense vegetation for shelter during the day, with easy access to grasses and pasture species at night.

But the grey and brown coloured animal was considered a major threat to indigenous forests compared to its impact on exotic forestry and pastureland.

LWQS committee member Ian McLean said wallabies were damaging forest and lakes Okataina and Tarawera, along with other lakes.

Damage to the under-story of these forests, causing erosion, would have a flow-on impact to water quality in the lakes.

"What's just as bad, wallabies are slowly but steadily spreading from the current infestation near Rotorua."

They had been seen on the outskirts of Tauranga and along the Rangitaiki River to the east - a small step from the main ranges.

"Once there they would add to damage done by deer and opossums - not only would the forest suffer but also lakes and streams," Mr McLean said.

"Dealing with wallabies now would be a small fraction of the cost of eradicating them from the Kaimais and Urewera."

Pest control approaches by authorities to deal with the wallaby have included trapping, exclusion fencing, night shooting and poisoning - but Mr McLean said more research was needed to assess and respond to the threat.

The other major theme of the symposium was lakeweed, which was becoming a growing problem in Rotorua lakes as they became clearer.

Lakeweed stopped some lakes and bays from being used for swimming or boating, and also created a smelly mess when it piled up on shore.

Among the scientists giving talks at the symposium would be Dr John Madsen, a leading expert on lake weed and based at the University of California.

"The Rotorua Lakes Restoration Programme was initiated by LWQS efforts and is showing tangible signs of success," Mr McLean said.

"But more remains to be done. This symposium deals with two significant but neglected current issues - they are important for the future of our lakes."