Some of Aotearoa's highest forests crumbled in the face of Cyclone Gabrielle due to deer being "way out of control" and destabilising the environment, says conservationist Dean Baigent-Mercer.
To secure high-altitude native forests against future storms, New Zealand must take urgent action to get introduced predators under control, he tells Mark Leishman.
The Japanese Sika deer was introduced to New Zealand in 1905 Photo: New Zealand Safaris
Environmentalist Dean Baigent-Mercer Photo: YouTube screenshot
Understanding how nature works is at the heart of building resilience against both the destruction of forests and the disastrous effects of travelling forest debris, says Baigent-Mercer, who is a Forest & Bird Conservation Manager.
In a healthy forest, about a third of rainfall is broken by the canopy, another third runs down tree trunks and the rest is absorbed into the moss covering the forest floor.
Yet in the Kaweka and Kaimanawa Ranges now, a lot of this precious native moss has been eaten away by Sika deer introduced from Japan in 1905.
"You know what sponge is like, it's like a dishcloth. It expands with water and slowly releases as it dries out over weeks or days, and then that evaporates. It dries out and then expands again when it rains … Moss is really important in terms of slowing water through native forests.
"Something that could have helped hold the land together and slow the speed of water is gone because we haven't kept up with deer control.
"We haven't allowed nature to do the best it can do with its own natural resilience in terms of movement of water."
Photo: Kennedy Warne
To preview the dangers of this, we can look to the transformation of Greece, Baigent-Mercer says.
Until around 2000 years ago, when the Romans invaded, Ancient Greece was covered in the Mediterranean rainforest.
When the Romans chopped down forests to make ships for war and introduced goats, Greece became the rocky, goat-filled place we think of today.
To make sure New Zealand doesn't go the same way, we need to get over the false belief that wild deer don't cause any trouble, he says.
In the Gisborne District, Ngāti Porou iwi has an "amazing plan" to turn around the collapse of the Raukūmara Range forest with deer culling.
Since Cyclone Gabrielle, erosion caused by deer in the headwaters has turned the ocean cloudy and the holes that crayfish live in are filled with sediment and gravel, he says.
"Everyone [on the Raukūmara Pae Maunga Restoration Project] is working together because they can see how much pain the forest is in and they're experiencing it because they live at the lowlands and they can see the effect of deer, even in the ocean.
"They're pulling out all the stops to turn around the collapse of that forest, and that's what needs to happen around the country as part of [building our national] resilience against cyclones.
"Technology is on our side, we can turn things around. We just have to have the political will."
The Raukūmara Range Photo: DOC
New Zealand needs a multi-generational commitment not only to pest control but river restoration and wetlands restoration, Baigent-Mercer says.
Once appalled by the idea of personally killing a possum, he now understands the necessity.
"I was vegetarian for a long time and when I bought my place, which has forest… I'd never killed a possum. I was horrified at the thought of it. But I had to change how I felt about it and changed my own behaviour because I realised no one else was going to protect the forest except for me. No one else cared about it and if I didnt do anything it would die and so would the birds and everything else."
When it comes to the methods of protecting our native species, New Zealand is "caught between a rock and a hard place", Baigent-Mercer says.
"Either we consent to doing pest control and saving forests and threatened species or we consent to them being killed. That is the moral dilemma and I'd rather be on the side of bringing the native species back to life."
