Service head Peter Mooney advised staff in writing last Tuesday that he must chop 20 positions in response to a $4 million budget cut this year.

He said half the positions had been found through natural attrition - mostly retirement - but 10 staff would be put on a six- month redeployment list.

"We have been reviewing administration and field support staff delivery across the service to identify where low-priority duties can be reallocated or forgone," Mr Mooney said.

"For those who are (affected) every effort will be made to find suitable funded vacancies."

It is the second time in two years that the state agency has faced significant cuts after the government first slashed its budget by $16 million and then boosted it by $10 million.

The service is also dealing with declining park visitors and expecting extra reserves to manage next year under the state-federal forests deal.

Community and Public Sector Union state secretary Tom Lynch said the 40-year-old service had nothing to celebrate.

"This is another blow to the service's staff who had jobs cut in 2009 only to have additional funding and recruitment of staff as an election pledge, and now those jobs are being cut again."

Mr Lynch predicted further jobs would go as revenue declined.

Environment, Parks and Heritage Minister Brian Wightman said like all parts of government, the service had to find savings.

He said $2 million, or half of its target, was found in non-salary measures.

"The service has an excellent reputation all around Australia and the world and will continue to manage and protect our national parks and reserves and to provide a first-class service to visitors to our parks," he said.

Mr Wightman said any parks or reserves created under the forests deal would be funded under that agreement.

The service manages almost 40 per cent of the state with 19 national parks, more than 400 reserves and three World Heritage areas.

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