Native habitats are increasingly unable to store carbon because introduced pests are chewing through forests, shrublands, and tussocklands, new research says.
For the first time, Forest and Bird research has linked the habits of browsing pests to carbon emissions.
Its report, Protecting our Natural Ecosystems' Carbon, released today, warns pests have a devastating effect on the environment and its ability to store carbon.
"The possums, deer, wallabies, goats, pigs, chamois, and tahr that were released into the wild have been chomping their way through native forests, shrublands, and tussocklands," said Forest and Bird chief executive Kevin Hague.
"This has destroyed the natural ability of native ecosystems to be the best carbon sinks on land."
Hague said naturally, native ecosystems could store huge amounts of carbon - but they could not if they were being munched on.
The numbers of deer, goat and possums are out of control - and it could topple carbon-holding forests, he said.
"When native forests collapse, huge volumes of carbon dioxide are released as trees die and rot," Hague said.
"Our largest forest type is presently bleeding 3.4 million tonnes of CO2 every year," he said.
"Impacts are multiplied if more than one invasive species of browser is present. They are killing our native habitats and causing native forests, shrublands, and tussocklands to release carbon instead of sequester it.
"By eating seedlings and killing young trees these introduced pest animals also consume future generations of forest, and our future carbon sinks."
Natural carbon sinks could be restored, and native plants and wildlife protected, but action was needed now, Hague said.
Increased control, coordination, and research into reducing browsing pests, and restoring the carbon sequestration of native ecosystems would help, he said.
Controlling animal pests to the lowest possible levels would increase the carbon sequestration, or the amount of carbon dioxide that could sucked from the atmosphere, by an estimated 8.4 million tonnes of carbon dioxide per year, the report said.
That was equal to nearly 15 percent of New Zealand's 2018 net greenhouse gas emissions, Hague said.
"Also, farmland that is currently being retired and allowed regenerate as well as newly planted permanent native forest sinks will need protection from browsing mammals too or all that work will be wasted," he said.
"Healthy native habitats are our biggest ally in the fight against climate change."