A report from the GLA shows some 2,500 acres of green space have been swallowed up by development between 1989 and 1999.
Residents told the authority's investigative committee that dog fouling made many green spaces unusable and parents were reluctant to let their children play in local parks and woods.
The threat to green spaces was compounded by the lack of political priority attached to the issue, and the decline in spending on maintaining inner-city green spaces across the UK.
It recommended the mayor's strategy include provisions to ensure the creation of green spaces in future developments.
Roger Evans, chair of the committee, said: 'The GLA must establish a clear vision for the city's green spaces and a strong planning framework to ensure they are protected for future generations.'
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