The role of the private tree in bringing diversity and resilience to the urban forest

Abstract

The urban forest is important for ecosystem service provision such as rainfall interception, pollution reduction, and biodiversity value. These provide health and wellbeing benefits to people living in urban areas and, with climate change projected to increase extreme weather, the importance of urban trees is likely to increase whilst at the same time putting the urban forest at increasing risk. The urban forest is composed of trees in both public and private ownership. How this ownership status impacts the characteristics of urban forests in Great Britain such as structure, composition, and health is not well known. We used a large database of 18,632 trees to compare the private (10,300 trees) and public (8332 trees) elements of 19 urban forests in Great Britain. We show that trees in the private urban forest are, for a given trunk diameter, 20% shorter and have an 18% smaller crown area. The private urban forest has a 9% lower tolerance for waterlogging stress; however, is 40–57% more diverse across taxonomic levels, hosts double the number of non-native species, and has 6% better tree condition. Management of the urban forest to reduce tree height and crown area reduces the provision of many regulatory ecosystem services. However, the better health and diversity of the private urban forest likely bolsters resilience to climate change and novel pests and diseases, indicating the importance for strategy and policy to recognise and work with those who own and manage private urban trees.