The true environmental cost of a fire that destroyed 500 hectares of the Waituna Wetlands Scientific Reserve last month may never be known.

Department of Conservation Murihiku and Southern Islands area manager Andy Roberts said there was no way to quantify the impact of the fire on wildlife and plant species in the reserve and the adjoining Awarua Wetlands.

"The fire occurred in the height of the bird-nesting season so lots of nests would have got lost. There would have been an impact on the wildlife," Mr Roberts said at a Southland Conservation Board meeting yesterday.

Some of the area's freshwater fisheries may have also been affected, he said. "Some of the streams were choked up with ash."

More than a quarter of the land area of the reserve was burnt when a fire, fanned by a strong northwesterly wind, raged through one of the largest remaining wetlands in New Zealand, he said.

Staff from the rural fire authority, Invercargill City Council and DOC were joined by helicopter crews carrying monsoon buckets of about 1200 litres of water from the nearby Awarua Bay to douse the flames, and an incident command centre manned by two members of the Invercargill fire brigade.

While the area is recognised for its biological diversity, cultural values and bird life, the damage could have been worse, Mr Roberts said.

Ground conditions were quite damp so the fire did not penetrate the ground layers, he said.

"If it had been later on in the summer and things had dried out we could possibly still have fire crews down there digging holes in the ground and putting water in there."

A recent survey by a team of DOC staff at the site of the fire found recovery in the vegetation, he said.

The wetland area had not been burned for nearly 50 years and was in fairly good condition, so the damage caused by the fire was quite disappointing, Mr Roberts said.

The focus would be to allow the area to naturally regenerate but colonisation by weeds would need to be monitored.

If there was a suspected cause and enough evidence to convict someone, the Southern Rural Fire District would take further action, Mr Roberts said.

Southern Rural Fire Authority spokeswoman Sally Chesterfield said the cause of the fire was still being investigated.

- © Fairfax NZ News

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