Living in urban environments, especially for those living in relative poverty, has been associated with high levels of stress and poor mental health.1,2 Such non-communicable diseases form a growing part of the burden of ill-health in an increasingly urbanised society, and offer challenges for healthcare provision. Socio-ecological models of health acknowledge the potential for the physical environment to have pathogenic or salutogenic effects3 but addressing today’s health challenges requires an integration of health issues into spatial and urban landscape planning, taking into account the potential for multiple health and environmental effects, and acknowledging possible unintended outcomes. There are many difficulties in determining how to guide and regulate such planning approaches in the context of other demands for sustainable and cost-effective urban development.4 4-6 Prüss-Ustün et al. (2016, p. 474) have suggested that “Investing in environmental interventions pays off for governments; it reduces the transfer of hidden costs from other sectors to the health sector”.6 However, little is known on whether environmental interventions can enhance mental health and, if so, what characterizes the planning and implementation of effective interventions. This paper addresses this challenge by assessing the effectiveness of environmental interventions in the area of urban green space, forestry and health, using a quasi-experimental approach to provide evidence that can inform government policy-makers, land owners, stewardship communities, practitioners and non-government organisations engaged in supporting community health and wellbeing