Areas of Scotland's forests are being offered on long-term leases to wind-farm developers as Alex Salmond surges ahead with his vision to make Scotland a world-leading green energy powerhouse.

An increased emphasis on turning over state-owned woodland to the renewables sector will see the number of power-generating wind turbines in forests increase. Between 700 and 1,000 turbines are expected to be erected on the National Forest Estate.

It is part of an ambitious target-driven policy championed by the First Minister to generate the equivalent of 100% of Scotland's electricity demand from renewables by 2020.

Nearly 60 square miles of forest are already being used for operational wind farms in Scotland. Under the plans, at the current rate, this figure could soar to some 240 square miles.

Plans to sell off England's public forest estate were abandoned by the Coalition after an expert panel said woodlands should remain in public ownership. It had been feared as many as 340 Scottish jobs could have been at risk had a UK-wide privatisation gone ahead.

Linda Holt, spokeswoman for Communities Against Turbines Scotland, condemned the expansion of the current policy, saying it would be challenged in the courts.

She said: "The Scottish Government may think it is entitled to turn publicly owned forests into wind farms but such a policy flies in the face of the Forestry Commission's own policies, local and national planning policies and the Scottish Government's commitment to increasing biodiversity.

"The Scottish Government is championing one industry, wind power, at the expense of another."

She added: "Forests are some of the worst places to build wind farms because they involve extensive tree-felling to create access and airspace for efficient turbine operation.

"There are major environmental 'disbenefits' and recognised major fire risks. I would expect there will be legal challenges."

The extent of the wind farm network was revealed when Finance Secretary John Swinney's budget on Thursday talked about an "advance" of "the next phase of renewables developments on the national forest estate".

Graeme Pearson, Labour MSP for South Scotland who chaired a Scottish National Wind Farm Conference last year, said: "There are many communities in south Scotland who have made representations to me about the environmental impact of wind farm development and the lack of consultation with communities to let them know how it affects them.

"One would hope the Government will be clear what this next stage means and that the communities are well aware of its impact."

The Forestry Commission Scotland (FCS) said the amount of electricity generated by the expansion would be enough to power one million homes a year.

An FCS spokesman said it had opted for leasing agreements with developers so the land would remain in public ownership.

It was estimated at the beginning of last year that the Forestry Commission would gather £30 million a year in rents but critics believe the figure represents only 10% of the profits energy giants will make.

The spokesman added: "The Scottish Government needs around 16GW of installed renewables capacity to meet its target of 100% of all consumption from renewable sources by 2020. Developments on the national forest estate could contribute nearly one-eighth of this.

"It's probable that some trees will be felled, but one of the key components of the Scottish Government's policy on the control of woodland removal was guidance on compensatory planting for any felling."

The Forestry Commission has already leased land to Scottish Power, which is owned by Spanish giant Iberdrola, German-based E.ON and Norway's Fred Olsen Renewables.

Data shows that since 2007 about 26,000 acres of publicly owned woodlands have been sold off, generating a profit of more than £28m.