A native orchid has been wiped out and rare trees hacked down in the name of roadside maintenance in the Waipoua Forest Kauri Sanctuary.

The Waipoua Forest Trust (WFT) has accused New Zealand Transport Agency (NZTA) of putting kauri and other species under threat due to the mismanagement of the roadside on State Highway 12.

NZTA has admitted some maintenance practices along the road corridor have not been up to scratch.

Network manager Tim Crow said that while failures had occurred, "there is no evidence that the forest is under threat".

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A report sent to NZTA and the Minister of Transport by WFT outlined serious breaches of a Highway Management Plan established in 2000 with input from WFT, local iwi Te Roroa, Department of Conservation and other stakeholders.

The breaches included the chainsawing of a rare tree daisy, weedspraying endangered orchids and failing to control invasive weeds. Concerns were also raised about the potential spread of kauri dieback disease, WFT chairman Keith Stewart said.

Auckland Museum's Curator of Botany, Ewen Cameron, has also spoken out about the destruction.

"The road through Waipoua Forest Sanctuary traverses one of the botanical marvels of New Zealand," Mr Cameron said. "It is imperative that the roadside vegetation is managed with great care."

NZTA had carried out a site assessment after receiving WFT's report and will appoint an independent consultant to audit roadside work and establish the Waipoua Forest Management Plan Liaison Committee to review the plan.

WFT member Stephen King monitored roadside work until a year ago when NZTA switched the contract to an iwi body. Mr King said one native orchid, the tutukiwi, had since been "wiped out". It was one of several naturalised orchids on that stretch of SH12.

While rare native plants were being sprayed with weedkiller, invasive and noxious plants were not being targeted, WFT claimed.