They spoke out following this week's release of the localism bill, which aimed to give greater power to local people.
Chair of GreenSpace East Paul Van Damme said: "The key issue is considering what professional expertise you need to keep the services running. You have to balance duty of care with looking after the park."
The Institute of Chartered Foresters said the plans to increase community ownership of forests in England needed to be centred on the skills of professionals. Executive director Shireen Chambers warned: "Communities need the resources to take on management and Government plans need to take account of this."
Paul Nolan, chair of England's Community Forests, agreed: "Professional input enables communities to get the most from their involvement. Communities value the fact that they are able to come to organisations for advice. We help them avoid problems and provide training to encourage ongoing involvement."