How much of the red zone needs to go green to support native birds?
OPINION: At Greening the Red Zone, we often get asked this question: "Why do you want so much?"
And it's a good question – because it's easy to think that by asking to return as much of the red zone as possible to nature, we're being just a bit greedy.
But it's not what we want that matters: It's what our wildlife needs.
Our native birds will only come back to Christchurch if there is enough habitat for them.
And what qualifies as "enough habitat" depends on the bird.
Let's take tui – a gorgeous songbird that just happens to be our mascot. Tui have a home-base territory of at least 1 hectare each. That's the minimum they need to survive.
A healthy population of any species needs at least 200 individuals. Any fewer than that requires constant human management to prevent inbreeding – and constant human management costs money.
So a self-sustaining population of tui – one that doesn't require human intervention – will need at least 200ha of habitat in the Avon-Otakaro Forest Park.
To survive long-term, nectar and fruit feeders need enough plants producing that nectar or fruit. Taking tui as our example again: kowhai, tree fuchsia, and harakeke flowers, coprosma, kahikatea, and totara berries – indeed, almost all our native plants – will entice them back into the city.
Those nectar and fruit feeders include bellbirds, and even kereru, which eat at least some of the same food as tui. If we want these birds back in abundance we need to provide enough food to sustain healthy populations of all of them.
Different birds have different needs – some of our native birds are carnivores.
One of the most endearing is our native owl – the ruru, or morepork. Ruru eat insects, small birds, and small mammals, and need abundant supplies of these creatures to survive.
Many people say how much they'd love to see ruru back in our city. But these little native brown owls need even more forest than tui – around 4ha per individual, in fact. To have a healthy ruru population, we need over 800ha of their preferred habitat. That's more than the entire red zone.
And then there are parrots. Wellington has had huge success reintroducing the charismatic – and more than just a bit cheeky – kaka, a forest-dwelling parrot.
Kaka have spread out into Wellington's already well-forested city, from a safe base within the Zealandia ecosanctuary.
Greening the Red Zone supports the proposal to establish an eco-sanctuary in the eastern reaches of the red zone, joining up with Travis Wetland.
But if we want a sustainable population of kaka in the city, they will need habitat outside the proposed 180ha of the Waitakiri Ecosanctuary.
How much? Kaka require large tracts of forest – their home range size is anywhere from 20 to 240ha.
At a minimum, a sustainable kaka population in Christchurch will need 4000ha of native forest throughout the city. We can make a start by providing a substantial base in the red zone. Reforesting tracts of Banks Peninsula could provide much of the rest.
So back to the question: How much of the red zone do we want? So far, I have looked only at forest birds. A lot of the red zone is natural wetland, that if returned to nature would provide habitat for birds such as kotuku and our nationally endangered bittern (known to be breeding in Christchurch).
Add wetland to the forest requirements, and it becomes clear that to bring sustainable, thriving populations of our native birds back to Christchurch, at least 80 per cent of the 530ha covered by the Otakaro/Avon River Corridor Regeneration Plan needs to be returned to nature.
Of course, there must be room for environmentally friendly human activity – walking, cycling, and horse-riding trails, picnic spots, art trails, and natural playgrounds. Eventually, once the forest has matured, zip-lines, canopy walks, and adventure courses. But those activities should not be at the expense of the habitat our birds need. They should work with it.
By reforesting the red zone, we can achieve a green corridor stretching from Hinewai and other heritage reserves of Banks Peninsula to New Brighton – providing enough habitat for birds such as kaka, ruru, tui, kotuku, bitterns, and more.
Following the devastating effects of the Ports Hills fire it is more crucial than ever for Christchurch to create this urban national park.
That firestorm, which destroyed years of effort put in to regenerating native bush in and around Ohinetahi, showed we need more than one place of safety if future generations are to enjoy their birth right and live among our native birds.
This is our chance to save our taonga (treasured) bird species and restore them to their proper place in our city. Here, with us, living every day. Not some distant memory we forever regret.
Dr Amanda Black is a senior lecturer at the Bioprotection Research Centre, Centre of Research Excellence, Lincoln University, and a committee member of Greening the Red Zone.