Landscape and green space consultant David Evans said he was frustrated by guidance from the Forestry Commission, Natural England and Landscape Institute.
"All have made policy guidance stressing the importance of green infrastructure. What's frustrated me is that it hasn't been joined up by debates in the green space sector. It hasn't really looked at the long-term funding and management implications," he told last week's GreenSpace conference.
"The main emphasis is placed on planning new green infrastructure in new developments, but can that be sustainably managed in the long term?"
One of the policy documents in question listed essential criteria, such as community engagement, and desirable criteria, such as funding. Evans disagreed with such assumptions.
"I don't think community engagement is essential for all green-space infrastructure but funding is crucial," he said. "You can't plan and design green infrastructure without having the right mechanisms in place for management and long-term running."
Evans said the categorisation threw up problems because no two spaces were alike and a lot of green space was "incidental", such as roadside verges. He went on to say it was unrealistic to expect the community to engage in the management of such areas. They wanted to be engaged in spaces that inspired them.
"You also have to think of long-term sustainability if you are looking to protect the space from future development," he added. "Getting the community to engage is certainly not a cheap option - it takes time, money and resources, and that's at odds with cutting costs at local authorities."