Plant-based feast

Why it’s a boom year for kākāpō and rodents alike.

Written by       Photographed by Andrew Digby

Andrew Digby

The job requires an iron gut. Over February and March, a helicopter flies transects over the country’s beech forests. Every 100 metres, the pilot lowers the chopper into the crown of a beech tree.

As it hovers, someone with absolutely no susceptibility to motion sickness leans out the door with a pair of secateurs and cuts off the tip of a thrashing branch. Back at base, the seeds on each branchlet are counted.

This year the Department of Conservation sampled more than 5000 beech trees, 3000 rimu trees, and snow tussock at 63 sites. The results have just come in: “The trees have gone apeshit everywhere,” says DOC ecologist Graeme Elliott.

That means 2019 is a beech-mast year—when the trees put forth a feast.

Masting is a defense strategy designed to saturate the environment with seeds, so that even if animals gorge themselves, some seeds survive. A beech mast occurs every two to six years, with different areas of forest on different schedules. The 2019 mast is predicted to be the biggest on record, involving 90 per cent of beech forests.

The extra food source is a boon for birds—at first. Their numbers surge over winter, but so do those of rats and stoats. By spring, the beech seeds are gone. Predators turn to birds, lizards, insects and bats instead. (Predator plagues caused by rare back-to-back masts in 2000 and 2001 wiped out several populations of threatened birds.)

DOC has known for about a year that this mega-mast was on the cards—the helicopter sampling just confirmed it—thanks to a new weather-based model: when a cool summer is followed by a warmer summer, many plants mast the summer after that. The bigger the temperature difference between the two years, the bigger the mast are produced. (How the plants measure this is still under investigation.)

Knowing mast size and area a year in advance allows conservation managers such as Elliott time to plan and to concentrate pest control where it’s most needed: “Over my lifetime I’ve seen mohua populations and bat populations blink out—and it happens during these rat and stoat plagues in the mast years.”

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