PESTS CHOMP THROUGH CARBON HOPES

Forest-munching pests colonised a third more conservation land in the past eight years. DOC admits publicly owned forests are a reservoir for pests but says farmers are also part of the problem. Eloise Gibson reports.

Forest-munching hooved animals have spread out and colonised almost a third more conservation land during the past eight years – just as the Government was beginning to realise pest control could boost carbon stocks.

Feral deer, goats and pigs now roam 82 per cent of the conservation estate, up from 63 per cent in 2013, according to Department of Conservation (DOC) monitoring.

Wildlife conservation group Forest & Bird believes that is an underestimate and is pushing for a huge boost in Government funding for controlling wild ungulates (hooved animals) to prevent more damage to carbon-rich native forests.

‘‘Unless there is urgent intervention, our country’s largest living carbon sinks are on a death watch,’’ said the group’s chief executive Kevin Hague.

The lobby group used conservation department data to create maps showing where the problem is most intense. It said pests were also spilling from public land and onto ‘‘massive swathes’’ of farm, forestry, and privately owned conservation reserves.

State-owned farming company Pāmu issued a statement confirming it was seeing a rise in pests on land it farms, which was making it harder to use trees for controlling erosion and reducing nitrogen pollution of waterways.

‘‘We have established forestry and erosion control and riparian plantings on our East Coast and northern Hawke’s Bay farms and began pest control to give the plantings the best chance of survival, but the numbers of pests, particularly goats and deer, are making this very challenging,’’ said Pāmu environment manager Gordon Williams.

‘‘Even our farm staff were unaware of the scale of the problem, and we are likely underestimating the pests within the wider landscape.’’

Asked if publicly owned forests were acting as a reservoir for pests, Dave Carlton, DOC’s project lead on biodiversity threats, acknowledged public forests were part of the problem – but said farmers who were previously happy to have a ‘‘few deer’’ out the back of their properties were also contributing.

Carlton said pests on DOCmanaged land were ‘‘part of the issue, but it’s a little more complicated than that’’.

‘‘The deer numbers have built up in farm/forest fringes as many landowners have historically been happy to have a few deer out the back of the property. In the past they would not have agreed to control of these deer or granted access through their property for recreational hunters,’’ he said.

‘‘These herds have increased due to access to good grazing and little hunting pressure and are now causing impacts in rural areas, regardless of the ungulate populations on public conservation land.’’

Pest culling with aerial poison such as 1080 has sometimes caused tension between DOC and hunting groups, who value having wild deer for sport and venison. The department has sometimes added deer repellent to its bait drops.

But if populations get too high, heavy browsing mammals can damage forests, compete for food with native species and eat out the forest understorey, preventing young forest regenerating when mature trees die. That could have devastating consequences for the country’s climate impact as well as the forests.

The Government plans to embark on a plan to measure how culling pests could boost carbon storage in native forests, as part of its proposals to slash the country’s emissions.

According to a recent Government document, ‘‘large-scale pest management offers the best chance of improving climate outcomes’’ from the country’s native forests – possibly offsetting some pollution from cars, factories, farming and other activities. The Government plans to have a work programme to test this theory designed by the end of 2021.

New Zealand’s indigenous forests store an estimated 1.7 billion tonnes of carbon (or around 6.5 billion tonnes of carbon dioxide) – the equivalent of 80 years of New Zealand’s greenhouse gas emissions.

But the Climate Change Commission, the Government’s independent advisory board on climate change, was told during its public consultation that pest numbers were too high to establish new forests in many regions and young trees

Kevin Hague Forest & Bird CEO were at risk, especially from growing numbers of goats and deer. It recommended ‘‘urgent and ongoing pest management’’ to protect native forests and their carbon.

Private forestry consultants, and Forest & Bird, have warned previously that carbon (some of it locked up for centuries) is at risk from devastating pest numbers, on both public and private land.

Although the Government currently has no recent estimates of how much the nation’s carbon coffers could benefit from pest control, a previous report by Forest & Bird estimated a blitz on invasive mammals could let established native forests recover to the point where they sucked in 15 per cent of New Zealand’s yearly greenhouse gas emissions.

Counting pellets

For its pest maps, Forest & Bird analysed data gathered by DOC, including its monitoring of the distribution of different pests throughout New Zealand and counts of faecal pellets (animal droppings) in a series of 1m-radius monitoring plots dotted around New Zealand’s

conservation land.

DOC uses a national monitoring programme to assess roughly 1400 sites evenly spaced across conservation land. A random sample of approximately 280 of these sites is measured between September to May each year, by conservation workers hand-counting the pellets. This is the monitoring that shows ungulates (deer, goats and pigs) spreading out to cover roughly 82 per cent of public conservation land at the last count, ending 2021.

Forest & Bird looked at how many pellets were counted at each monitoring site, and dubbed places with 200-1200 faeces per 1 metreradius plot ‘‘high’’ in ungulates, and places with 1200 – 4765 faeces per 1m plot as being in ‘‘crisis.’’ The group acknowledged it was hard to find a scientific threshold for how many pests are too many for a forest’s survival, so those labels were its interpretation of an unsustainable level.

Monitoring pests on private land can be more difficult than on DOCrun land, partly because the droppings can be confused with farmed deer and other livestock.

‘‘Our country’s largest living carbon sinks are on a death watch.’’