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Police are investigating an attack on field trial of genetically modified trees near Rotorua.
A electrified perimeter fence at Crown research institute Scion's base was breached on Monday and around 20 pine trees chopped down in an apparent protest.
Scion had been studying how 80 radiata pine and Norway spruce trees reproduce.
Police said that a hole had been dug under the fence and allowing somebody to burrow underneath.
A spade bearing a GE Free New Zealand sticker was left behind.
Scion said it was reviewing the breach and looking at whether any genetically modified material could have been removed.
Lobby group, the Soil and Health Association, which has been calling for the trees to be cut down, said it hoped the breach would prompt Scion to improve security around the fence.
Association spokesman Steffan Browning it did not condone illegal acts but the experiment had been poorly run.
He said Biosecurity NZ had indicated it would investigate the breach.
The association had previously reported compliance breaches by Scion, and yesterday's news had raised concerns of GE plant material being removed from the secured area, he said.
"The Environmental Risk Management Authority have said that there appeared not to have been material removed by those involved in the cutting down of GE trial trees.
"However, rabbits appear to have been risking that ever since the trial started...infesting the trial plot and surrounds."
The civil disobedience was not surprising, Mr Browning said.
"Considering overwhelming opposition to genetic engineering in New Zealand, field trials should be treated as a privilege and run to the highest level of precaution."
- NZPA
