Bournemouth Borough Council has rubber-stamped proposals to sell the land - which includes children's play areas and a war memorial site - as part of its new playground strategy. The 4.8ha of green space was earmarked for sale following a review by the council's leisure services department and property, planning and housing department.
The review concluded that the 18 spaces are "low-value open space" in terms of current or potential use levels, attractiveness and biodiversity.
GreenSpace chief executive Paul Bramhill said: "It seems to be flying in the face of where we should be going in the future.
"We should be trying to conserve as much green space as possible - that is not to say we should never have development, but green space's role in climate change and food production should now be at the forefront of the decision."
The strategy aims to allow Bournemouth Borough Council to provide higher-quality but fewer play areas said leisure policy manager Michael Rowland.
The council's cabinet has agreed that a proportion of money raised from land sales should be re-invested in green space, like in Bristol where 70 per cent is ring-fenced to support its green spaces strategy, but a sum has not been discussed.
"We have agreed the principle with the politicians but not a figure," explained Rowland. "It may be decided on a site-by-site basis but I would like to get as much funding back into parks as I possibly can."
Rowland added that the strategy includes plans to open at least 14 new play areas, from which no one would live further than 800m. However, standards launched by Natural England last year set a 300m limit on the distance from a green space.
Parks consultant Alan Barber said: "It seems inadequate policy-making to decide that the revenue produced from the disposals is needed to invest in the remaining play areas yet be unable to say how much money that will yield for the purpose, because nobody has said just what proportion of the receipts will be available."
Winton Community Forum is planning a campaign to save Fampoux Gardens, said chairman Anson Westbrook.