Introduction

The Department of Conservation has found a large area of beech forest in the Dingle Burn Valley near Wanaka that has been defoliated by mountain beech moth caterpillars.

The Department of Conservation (DOC) has found a large area of beech forest in the Dingle Burn Valley near Wanaka that has been defoliated by mountain beech moth caterpillars (Proteodes carnifex).

Backcountry users will notice forest affected by the moth has turned grey-brown and appears to be dying. Several hundred hectares of forest has been affected.

DOC Otago Botanist John Barkla discovered the defoliation while monitoring a nationally endangered plant – Pittosporum patulum – present in this valley. He said it was a periodic natural event and, from time to time, whole tracts of sub-alpine South Island forests are affected by the moth.

“We don’t need to consider artificial control methods because the moth numbers will fall dramatically after the epidemic and mountain beech has a natural ability to refoliate. We expect the complete recovery of healthy trees because both caterpillar and host have evolved together over a long period of time,” Mr Barkla said.

He added that trees at the upper forest limit or those weakened by old age may suffer partial crown death and in some cases may die. Because defoliation allows more light to fall on the forest floor, an uncharacteristic mat of vigorous grasses and weeds can develop, which can adversely affect seedling growth.

Caterpillars of this moth are usually found only on black or mountain beech but they occasionally occur on red and silver beech which are growing close to black or mountain beech. Silver beech forest at the uppermost limit of the Dingle Burn forest appears to be unaffected.

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