A large number of studies have provided evidence that ecosystems with a high level of biodiversity are more likely to be more efficient in providing high levels of multiple ecosystem services (aka biodiversity-ecosystem functioning theory). Ecosystem services can be described as the ecological characteristics, functions, or processes that directly or indirectly contribute to human wellbeing, i.e. the benefits people derive from functioning ecosystems. Environments:

• provide food, fuel, fresh water, medicines and other materials (i.e. provisioning services)
• regulate local and global climate, air quality, pollination, pests and vector-borne diseases (i.e. regulating services)
• provide habitat for biological diversity and maintain genetic diversity (i.e. supporting services)
• offer space for spiritual, recreational and intellectual interaction with natural environments (i.e. cultural services).

Natural environments and green spaces provide ecosystem services that enhance human health and well-being.  

A growing body of evidence shows that many observed associations between exposure to green environments and human health and well-being benefits are mediated by a number of crucial ecosystem services. These include:

• cultural ecosystem services that have an impact on stress
• regulating ecosystem services that reduce harmful environmental exposure such as air pollution, extreme heat, urban heat and noise.

For example, high plant diversity may result in high structural and functional variation which determines the potential of green spaces to mitigate air pollution, potentially reducing cardiovascular diseases and premature death.