A silent battle is about to commence in New Zealand's forests

This post was chosen as Pick of the Week by Science Seeker.

New Zealand ecosystems often have quirky components that would not be out of place in a fantasy novel. Strange, wooden, rose-shaped structures form on tree roots where parasitic Dactylanthus plants await pollination by bats. Black velvet covering the trunks of southern beech trees is, on closer inspection, revealed to be a fungus, which feeds on honeydew excreted by scale insects feeding on tree sap. Native birds also depend on the honeydew.

New Zealand bush has some incredible ecology.

An ecosystem is like a jigsaw puzzle, with each piece an organism or natural resource that plays its part in the whole picture. The wonder of New Zealand's ecosystems is invariably eclipsed by the realisation that many are missing their pieces. The bats that pollinate Dactylanthus are declining in numbers. The honey-scented beech forests are now home to ravenous introduced wasp species, which raid the honeydew and out-compete native birds.

This is the story of New Zealand. Bizarre and incredible natural history is destroyed by introduced species and habitat loss. At times, conservation in a land overrun by introduced species seems hopeless. However, all is not lost. We have research, and we have weapons.

Ecologists have discovered another quirky bit of ecology that has developed since mammals were introduced. Southern beech trees have masting years, where they drop gazillions of tasty little seeds. It doesn't happen every year, and approximately every 15 years there is a particularly heavy mast (seed drop). Mice and rats eat the seeds, grow fat, and make lots of babies. Stoats cotton on to this plethora of fat little prey items, and they start to eat the mice and rats, grow fat, and make lots of baby stoats. This continues throughout the mast until there are a lot of seeds, a lot of rodents, and a lot of stoats. At the end of the mast, the trees stop dropping seeds, and soon the last few rot, germinate, or are eaten. The mouse and rat population stops growing, and the stoats start running out of rodents to eat.

But stoats can prey on other creatures.

Pretty little songbirds such as mōhua (yellowhead) and toutouwai (robin). Cheeky parrots, kea and kākā. Along with other endangered animals such as bats and invertebrates, these endemic species are killed in huge numbers when stoats go hungry at the end of a mast. So when a beech mast is detected (by sampling programs), the Department of Conservation (DoC) goes into action trapping and poisoning throughout forests all over New Zealand.

Kārearea and kea benefit from pest control

Some people believe the operation can be carried out using traps alone, and poison is not needed. Those people have not tried to run a trapping program in the deep, impenetrable forests of New Zealand's wilderness areas. A combined approach is effective, and results in bird numbers going up rather than crashing.

This year, pest control in South Island beech forests is particularly important, because we are expecting a MEGAMAST! Beech trees are dropping more seed this year than they have in the last 40 years. More seed over a large area of forest means more predators, and ultimately more death of native creatures, except that it won't, because DoC is increasing trapping and poisoning efforts. Thanks to extensive sampling, scientific research, and funding, DoC is able to predict the mast and respond to it.

Despite our ability to combat the devastation initiated by a mast, the coming months will be a testing time for native wildlife, and all pest control resources will be needed in the fight. If you live in New Zealand, you may be able to help by volunteering. There are also numerous local pest control groups promoting trapping in various areas around the country; click here to find and join your nearest group.