[Reprinted from original]

The Department of Conservation (DOC) is planning its largest predator control programme in response to a 'mega mast' event – exceptionally heavy seeding – in New Zealand forests.

The $38 million programme will cover about 1 million hectares of conservation land across the country (the previous largest was 840,000ha in 2016). Aerial 1080 operations will cover more than 900,000ha, and trapping will take place across more than 66,000ha.

Priority sites include Kahurangi, Abel Tasman, Arthur's Pass, Westland, Mt Aspiring and Fiordland national parks, the Caitlins and Whirinaki. The predator control effort aims to suppress rat, stoat and possum populations to protect native species.

Monitoring by DOC had confirmed a predicted mega mast, or heavy seeding in New Zealand forests this autumn, Conservation Minister Eugenie Sage said in a statement on Monday.

In a mast year, trees produce large amounts of seed. This boosts rodent numbers, and in turn stoat numbers. When the seed is gone, the plague of predators turn to native birds, bats, lizards and insects.

Environmental group Forest & Bird has warned the mast is likely to be the most widespread in 45 years, with more than 90 per cent of beech forests affected.

Sage said if DOC did not act, New Zealand risked losing native bird and bat species. Kiwi, mohua (yellowhead), kakariki (orange-fronted parakeet), kea, kaka, and rock wren were among the species at risk.

"Responding to the increased threat from introduced predators during such a big mast year is critical if we are to retain our unique native species that set New Zealand apart from the rest of the world," Sage said.

New funding of $81.2m over four years in Budget 2018 had allowed DOC to scale up its predator control programme to respond to the threat posed by the mast, she said. Forest & Bird chief executive Kevin Hague acknowledged the extra funds, but said DOC needed more resources.

DOC needed to at least double its existing annual predator control budget, Hague said. The mast was the biggest in 45 years, and predator control was essential to stopping localised extinction.

"The Government needs to throw everything they've got at this crisis, or we will lose species."

DOC predator control programme coordinator Pete Morton said the 2019-20 effort would involve several hundred people. The programme would crank up from May, reach a peak in late winter and spring, and continue into summer.

While most predator control sites had been confirmed and were at an advanced planning stage, operations would only proceed at mast sites if rodent numbers reached levels that could post a threat to wildlife.

Morton said doing predator control across 1 million hectares, or about 12 per cent of conservation land, was about the limit of what DOC could feasibly do. There was "seed everywhere", he said, adding it was like "nirvana" for forest animals.

"We've certainly seen mast events previously, but not one this widespread and this strong."

DOC seed sampling in February and March pointed to the biggest beech mast for more than 40 years, with exceptionally heavy seed loads in South Island forests. Rimu forests and tussock grasslands were also seeding heavily.

Morton said DOC generally used between 1.5 to 2 kilograms of 1080 bait per hectare. For 900,000ha, this worked out at a minimum of 1350 tonnes. The poison is the only tool currently available to knock back rodent populations over large areas before they reach plague levels after a beech mast.

"1080 is a safe and effective tool and it's used to protect our birds," Morton said.

"In the places we've used it, we've seen bird numbers bounce back."

DOC has been consulting with iwi, regional councils and other pest control agencies, community groups and neighbouring landowners as part of planning for the predator control programme.

An earlier version of this story said the predator control programme would use an estimated 1.5 million tonnes of 1080. This was incorrect