The ‘Healthy Parks, Healthy People Global’ initiative is a prime example of the research which is supported at a high level by National Parks Services in USA, South Africa and Australia. Additional projects such as ‘Rethinking Parks’ from Nesta in the UK also feature significant research which points to the many social benefits.
Social benefits could be grouped as:
Building Stewardship 
Building Community 
Building Physical and Mental Health & Wellbeing 
Pro-social Behaviour