GreenSpace business development manager David Tibbatts told a workshop at the GreenSpace conference last week that there was a clear need to improve the information base to provide evidence that parks' services had declined.
The GreenSTAT visitor survey system, which records users' views of green spaces, now had 25,000 responses.
It showed there were 3.8 billion visits to parks annually at a cost of 18p per visit, which created an important tool in the fight for more funding.
Tibbatts said to get out of a cycle of decline, park managers needed a baseline of information to show decision makers the popularity of services and where they were failing.
The benefits of improving parks need to be demonstrated and information provided to show the value for money based on annual visits and the cost per visit.
"But we still don't have much political support and there's still a lack of understanding of what green spaces can do," he said.