Beech boom may spawn tide of pests

Last updated 05:00 09/12/2013

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A looming pest plague could put rare Fiordland species at further risk next year.

Beech trees have flowered heavily this year, which could lead to the the biggest seeding in more than a decade - meaning more food for mice, rat and stoats which would cause an explosion in their numbers this winter.

The plague of predators could put rare bird populations at risk, the Department of Conservation (DOC) says.

DOC director-general Lou Sanson said the widespread flowering would generate large quantities of seed falling on forest floors next autumn and that abundant food supply was likely to fuel an explosion in predator numbers.

"Our biggest concern is that when seed supplies run out next winter, large numbers of rodents and stoats will turn on vulnerable species like threatened forest birds, endangered bats and New Zealand's unique giant land snails."

Beech generally seeds every four to five years, but climatic conditions over the past two summers - a cool summer followed by a warm one - appear to have triggered the onset of a bumper seed, or beech mast, year..

DOC scientist Graeme Elliott said there were signs the seeding event would be at least as big as the beech mast in 2000, which contributed to mohua numbers in Fiordland's Eglinton Valley dropping from several hundred to a dozen or so birds and wiped out a local mohua population at Mt Stokes in the Marlborough Sounds.

DOC Fiordland conservation services manager for biodiversity Lindsay Wilson said many beech trees were flowering in Te Anau and Fiordland, and staff were beginning to prepare for the potential fallout.

"We can't stop Mother Nature, but we can manage pest levels."

DOC staff in Fiordland would begin assessing sites and species most at risk, and extra monitoring and trapping was being planned.

Several vulnerable species in Fiordland, including the mohua and long and short-tailed bat populations, could easily be lost, Mr Wilson said.

Eglinton Valley's mohua population was almost destroyed by the last pest plague and was recovering slowly, so it was important to be able to protect them from another explosion in numbers of rats and stoats, Mr Wilson said.

There were now 100 to 200 birds after a transfer of 69 mohua from Chalky Island to the Eglinton Valley in late October 2010.

There were also populations of rare birds on predator-controlled Resolution and Secretary islands, but a boom in mice, rats and stoat numbers could lead to the islands' biosecurity being breached.

High numbers of stoats on the mainland could lead to some swimming to the island and, without pest control contingency plans, could put stress on bird, lizard and invertebrate species.

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- Southland


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