The so-called "mega-mast" which could unleash predators on native species looks like it's happening and the Department of Conservation (DOC) has been out in South Island forests to confirm the size and extent of it.
In January, DOC scientist Graeme Elliott said based on current predictions and historical climate records, it was looking like the most extreme mast for 20 years.
DOC Landscapes Manager Predator Free 2050 Peter Morton now says: "A DOC monitoring team has been busy over the last few weeks sampling seed from beech and rimu forests throughout the South Island to confirm the extent and size of the mast.
"While we won't have the final results of this work for several weeks, we've counted a large amount of seed everywhere we've looked so far, consistent with a big mast event."
Once the beech seed fell from trees in autumn it would fuel a rapid increase in rodent numbers, he said.
DOC would monitor rodent levels using tracking tunnels at all sites that had been identified as priorities for predator control.
"Monitoring data collected in February, May, August and November will show whether rodents reach levels that threaten native wildlife and therefore trigger the planned predator control operations," Mr Morton said.
"DOC prioritises predator control to protect our most at-risk populations of native species, threatened forests and areas of high ecological value across public conservation lands. The species at greatest risk in 2019 are kākāraki/orange fronted parakeets, mohua/yellow head, rock wren, long and short tailed bats, kiwi, kea, whio/blue duck and native snails."
This year DOC is planning predator control over about one million hectares - about 12 percent of conservation land - in response to the mast. That includes more than 66,000 ha of trapping.
Predator control at priority sites was at an advanced stage of planning but aerial 1080 operations would only proceed if rodent trigger levels were reached, Mr Morton said.
The aerial 1080 programme would begin in late autumn and was timed to knock down rodent populations before they reached plague levels and protect native birds before they bred in spring and summer when they were most vulnerable.
Aerial 1080 operations target rats, possums and stoats - through secondary poisoning from rat and possum carcasses.
People could help by trapping predators in their backyards and joining groups that supported trapping networks in nearby reserves and bush areas or in front-country conservation areas, Mr Morton said.
Masts aren't all bad
Despite the threat of predator population booms, forest masts did have benefits, Mr Morton said.
They provided native species extra resources because they put more flowers and seed into the forest ecosystem.
"At a time before mammalian predators were introduced the forest mast was a boon to native wildlife. Today, it still provides food for insects, lizards and birds and boosts breeding for forest birds like kākāriki, robin/toutouwai, rifleman/tītipounamu and mohu/yellowhead. Kākāpō rely on rimu fruiting to breed and this year is proving to be a bumper breeding season.