Department of Infrastructure, Energy and Resources secretary Norm McIlfatrick said a $25,000 grant was provided to each of the 10 signatories to the forestry statement of principles, $100,000 was provided to Forestry Tasmania to carry out modelling work and the department incurred a $283,000 cost.

Resources Minister Bryan Green said the government recognised that being involved in the process was a significant cost for some of the people involved.

Mr Green said it was now up to the state and federal governments to work through the agreement released by negotiations facilitator Bill Kelty last week.

He said he hoped a "reasonable package" would be developed, with any additional reserves requiring legislative protection.

Mr Green also denied Liberal claims that the forestry agreement - signed by environment and industry groups and the forestry union - would lead to 100,000 hectares of prime agricultural land being converted to plantations.

He said Tasmania had considerable plantation assets but that most were eucalyptus nitens plantations and would need to be converted to eucalyptus globulus - or Tasmanian bluegum - to meet the needs of the industry.

"What's achievable in that regard would be determined by market forces, not by decree," he said.

Mr Green also said there had been some speculation that an additional 10,000 hectares would be needed for plantations but that the figure had not been part of any modelling.

Opposition primary industries spokesman Jeremy Rockliff said the 10,000-hectare figure would come as a "huge shock" to many farmers.

"It makes absolutely no sense to turn even more of our productive farmland into tree farms, and at the same time lock up hundreds of thousands of hectares of production forest for the sake of keeping the Green-Labor government in power," he said.

Bass Greens MHA Kim Booth also used budget estimates to question Mr Green about the sale of Gunns' Triabunna mill and accused the government of being involved in a "deal sweetener" to bring about the sale.

Mr Green said he had no knowledge of such a deal and Mr McIlfatrick said Aprin, which has approached the Department of Economic Development for a loan to buy the mill, had been in detailed negotiations with Gunns before seeking the loan.