Deer, feral goats and pigs are an increasing problem in the Whanganui region, with Forest & Bird saying the density of feral grazing animals is one of the highest in New Zealand.
The organisation has created a series of maps from official data showing virtually all conservation land on mainland New Zealand, plus large areas of privately-owned land, are under attack from herds of wild deer, pigs and goats.
Forest & Bird is calling for the government's climate plan to urgently fund a significant deer, pig, and goat control programme to maintain important carbon sinks and the ecological health of native forests.
"The number and extent of wild deer, pigs and goats on all land types across New Zealand is at crisis levels," Forest & Bird chief executive Kevin Hague said.
"Our analysis shows that close to 100 per cent of native habitat has at least one species of deer, pig or goat on it, while two-thirds of primary production land is under invasion from these animals."
Feral deer, goats and pigs come under the 1977 Wild Animal Control Act, which is administered by the Department of Conservation (DoC).
Regional councils also have a role as protectors of biodiversity.
Some regional councils treat deer as pests but they are not pest animals in Horizons Regional Council's current pest management plan. However, the plan says browsers like goats and deer need to be managed to protect biodiversity.
Whanganui National Park had one of the highest deer and goat densities of any national park in New Zealand, former Whanganui resident and conservation worker Morgan Cox said, and in the Waitōtara Conservation Area anything palatable had been "chewed out".
"[Goat] numbers peaked around the '60s and since then their numbers have fallen simply because the forest is so degraded," Cox said.
"There's not as much for them to eat as there used to be."
DoC and regional councils have a role in controlling pests but currently only recreational hunters go after deer and pigs in Whanganui while DoC does some goat control on conservation land.
In Whanganui most deer are red or fallow. A fallow deer eats as much as one sheep, and a red deer as much as two, according to Deer Industry NZ.
Local hunter and farmer Neil Campbell said there were deer "everywhere now, masses more than there used to be".
"They're encroaching more and more. The bloody things are damn near in Victoria Ave. They're at the Belmont Golf Course and in Roberts Ave."
Like many farmers, Campbell has a few on his farm but keeps numbers down.
Atihau Whanganui Incorporation chief executive Andrew Beijeman has to balance the profitability of his farming enterprise against shareholders' desire to hunt deer for food.
The incorporation farms 21,000ha of hill country and most weekends there are hunters, with permission, on its stations.
The deer provided food for uri, descendants of the owners, but also ate grass grown for stock, made forest establishment difficult and stopped regeneration of native forest, Beijeman said.
"We are assessing that all the time."
In remote Watershed Rd, forester and farmer Hans Brink and fellow hunters shot 4000 goats to get pine forest established in the 1990s. There weren't many deer then, but the Brinks now clear 150 to 250 from the property every year.
In Whanganui National Park deer are impacting forest health by eating the palatable plant species, in some cases chewing through the understorey, ring barking larger trees and even eating the leaf litter, DoC's acting Whanganui operations manager Connie Norgate said.
DoC's control of ungulates (large hoofed animals) in the Whanganui District is centred around an annual goat control programme. Goats are more damaging than deer because they eat a wider range of plant species and are less favoured by hunters.
DoC relies on recreational hunters to control deer on public conservation land. But Norgate said deer had moved into the rural landscape, damaged many small reserves and QEII covenants and impacted on replanting projects and farm production.
"In past years many landowners didn't mind a couple of deer at the back of their property; however, in recent years deer have bred up into larger numbers in some cases."
Nationally, DoC is putting together the Te Ara Ki Mua strategy in response to the way deer have increased over the last two decades.
Cameron Ryan, a member of a group that wants to protect regenerating native forest on a rural Whanganui property, said that could not be done with feral deer roaming through it.
"Coming from an environmental perspective, to get anything to happen at the farm we will need to put a deer fence up because otherwise we will not be able to achieve forests that succeed for generations," Ryan said.
The main controllers of deer, goats and pigs were hunters, NZ Game Animal Council general manager Tim Gale said.
DoC might kill 1000 to 2000 deer a year, but hunters took about 135,000, he said.
Interest in hunting was growing and hunters wanted to keep deer numbers down in order to improve their quality, he said.
"We want healthy animals. To have a healthy animal you need a healthy habitat, so it's about getting that balance. No hunter wants to be going out and targeting skinny deer."
As a contribution to conservation, deer hunters were encouraged to shoot any goats they saw, he said.
Gale recommended shooting mature female deer and yearlings as the best way to keep numbers down, and saving stags for trophy heads.
"That's how we can have our cake and eat it too."
Gale said he believed a balance was possible, keeping both game animals and the environment healthy.
Gale and Norgate said landowners who wanted to control deer, goats and pigs needed to give more access to hunters.
