Urban green is equivalent to plant wealth, that is to say, to botanical biodiversity, forming in turn a support for animal biodiversity. What's more, the biodiversity found in big cities, and especially in their green spaces, is often the only opportunity that local inhabitants have to enter into contact with nature, and it provides environmental and social benefits that are of fundamental importance for improving citizens' quality of life and welfare. Cities advance by establishing a balance between urban activity and the support of nature and of their own biological diversity. Barcelona fosters the preservation of biodiversity through programmes for the conservation of flora and fauna and of the habitats where they live.

Green spaces are outdoor sites for leisure and the promotion of positive coexistence. This is why the city attends to the maintenance of its parks and gardens, tree spaces and forest areas according to criteria of sustainability and respect for the environment, equipping them with children's playgrounds, areas for elderly people, recreational facilities and off-leash areas for dogs.