Nineteen trees, some genetically modified, have been cut down in an apparent protest against Crown forestry research institute Scion.
Those responsible for the attack dug under the Rotorua institute's perimeter fence and left behind a spade with a sticker saying "GE Free New Zealand".
It is unknown exactly when the attack occurred but the trees were discovered slashed on Monday and police were called.
The felled radiata pine included both genetically modified and unmodified trees being grown as part of a field trial.
Police said last night they were unsure who was responsible for the attack but were conducting forensic tests on items seized at the scene.
Scion said it was the first attack of its kind at the property and there was no evidence that plant matter or soil had been removed by the saboteurs.
Acting chief executive Elspeth MacRae said even if this had happened, it would not pose a danger to the outside environment.
"The genes involved in this research were sourced from organisms that occur naturally in the New Zealand environment and are already present throughout the country," she said.
Scion would not allow the Herald to photograph the site, saying it was private property and remained part of an active police investigation.
The institute is located in a 114ha business park shared by other companies, next to Whakarewarewa Forest.
Formerly known as Forest Research, Scion manages forests and conducts research on genetically improving trees.
It also develops biomaterials, which are seen as a major potential export earner.
Biomaterials are natural resources transformed into industrial products using chemical, physical and engineering/manufacturing technologies.
Ms MacRae said Scion would review security at the institute in the wake of the tree incident.