People driving efforts to eradicate wilding conifers in Canterbury say they are slowly pushing back the tree invaders.
But they say it's going to take many years of persistent work by contractors and volunteers to stop the spread of the pest trees across the landscape.
Pinus contorta -- also known as lodge-pole pines -- and larches are the biggest threat.
Their uncontrolled spread over thousands of hectares of inland Canterbury, as well as Northern Southland, has invaded farmland, displaced native plants and wildlife, used up water resources and increased the fire risk.
Canterbury Regional Council's biosecurity adviser for special projects, Steve Palmer, says there are about 13 wilding conifer control projects running, most in the Mackenzie Basin.
He says they are making slow progress, with very limited financial resources .
One of the groups battling the wilding conifers is the Waimakariri Ecological and Landscape Restoration Alliance, or WELRA.
It had about 200 volunteers clearing trees from 700 hectares of high country at Flock Hill Station and Lake Lyndon over three days in March and April.
WELRA'S chairman, Ray Goldring, says the body has raised and spent almost half a million dollars on wilding control work in the past year, using specialist contractors and helicopter spraying for very dense areas.