The Greens are promising 720 new DOC rangers over the next five years, doubling the number of frontline conservationists protecting New Zealand's native birds and plants.

The party would also double the baseline funding the Department of Conservation receives, by 2021 and introduce a $20 tourist tax to raise $65m to carry on efforts in the Government's goal to be predator-free by 2050.

Co-leader James Shaw has unveiled the Green Party conservation policy calling it the "single biggest new investment in conservation" since DOC was established in 1987.

CHRIS MCKEEN/STUFF Green Party co-leader James Shaw has promised new DOC rangers and a doubling of the DOC baseline funding budget.

"Since taking office, the National Government has put DOC through the wringer, cutting hundreds of millions of dollars from DOC's baseline funding, forcing it to close field offices, and cutting the jobs of around 200 frontline rangers.

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"As a result, DOC is not being resourced do the job we expect of it: to protect all our unique wildlife, the places we love, and our experience of them," he said.

KAY MILTON The kokako has been upgraded from 'threatened' to 'at risk-recovering' by DOC.

Native birds were in "serious trouble".

"Waves of introduced predators and habitat loss have combined to create a perfect storm of destruction. One third are facing extinction. Birds like the kea or yellow-eyed penguin could disappear in our lifetimes," Shaw said.

Doubling DOC's budget would be phased in over five years, so by 2023 the department would be given an additional $192m in baseline funding.

BRENT TANDY / DOC Birds like the little blue penguin are protected by DOC.

From this, DOC would fund the rangers, technical staff and scientists and any additional operational expenses it required. Shaw also expected the funding to allow DOC to double the amount of pest control it carried out.

An addition $24m would would double the funding for community conservation work on private, QEII and Maori land. That funding, and the tourism tax would be in place by 2021.

The Greens would also ban all new mining on the conservation estate and afford greater legal protection to threatened species and their habitats.