Drone views of possum impact on ancient Coromandel forest

Hauraki - Newly released drone photography shows the impact of possums on a section of an ancient native bush in northern Coromandel, and also the value of predator control and restoring forest habitat.

The images were obtained as part of work undertaken by Department of Conservation’s (DoC) Coromandel staff.

DoC has been working on efforts to stop the spread of the tree disease myrtle rust and safeguard genetic seed stock for the species.

Myrtle rust has the potential to weaken and eventually kill some native New Zealand tree species such as pōhutukawa, manuka and rātā.

Trapping, poisoning and shooting has now reduced the possum population. But there are still about 30 million possums in New Zealand today.

The drone images show sections of forest canopy in the Papakai block of the Coromandel Forest Park in the Coromandel ranges.

Nick Kelly, DoC’s Coromandel operations manager, says the drone images show the stark contrast in the state of the native bush.

One area where there has been more than 25 years of predator control effort looks pristine while the other part, an adjacent section of land, has been devastated because predator control has only been undertaken twice in the last decade.

“The tops of the rātā trees in the two images are where the difference is really evident,” he says.

“In the area where we’ve had long-term predator control, you can see the distinctive red-brown colour of the rātā trees flowering — they’re good healthy trees, with plenty of leaf coverage and no signs of the damage possums cause.

“But in the other image, several dead rātā are clearly visible — over time, they’ve been stripped of leaves by possums and that’s led to the trees dying.

“Those dead specimens really stick out, and they’re a trigger for what we term a ‘top-down collapse’ of the forest eco-system.”

As larger trees die off due to the impact of possums, it compromises wider biodiversity and forest health, with birdlife, insects and other native wildlife affected.

DoC’s predator control efforts are essential to protect New Zealand’s native species, as introduced pests like possums, stoats and rats eat native plants, insects, birds and eggs.

The protected areas of the Coromandel ranges are home to important native species such as Archey’s frogs, Coromandel striped gecko and Coromandel brown kiwi.

In 1921, government made it illegal to bring any more possums to New Zealand. But by then, possums were already living in 450 different parts of New Zealand. They were not officially declared a pest until 1946.

Fiordland and Northland were the last areas of New Zealand to be invaded by possums. In the 1960s there were hardly any possums in Northland but in the 1990s — only 30 years later — there were 10—15 million possums living there.

People used to think that possums only ate plants. But in 1993 possums were filmed eating the eggs and chicks of endangered kōkako.

They have since been filmed eating the eggs, chicks and even adults of many other native birds including kererū, kiwi, harrier hawk, fantail, muttonbird, and tūī. They also eat the nectar and berries that native birds like to eat so that there is less food for the birds.

Possums carry a disease called bovine Tb (tuberculosis) which they spread to cattle. They also eat pasture so there is less food for farm animals. The damage done by possums costs NZ farmers about $35 million every year.

The government spends more than $110 million a year on possum control.