UK urban forests and the 3-30-300 rule

In the UK, cities are pushing for higher tree canopy cover, but does this bring an improvement in access to trees and greenspaces? Canopy cover estimates are valuable tools for measuring and monitoring changes in existing tree cover, but these percentages don’t tell us how trees, and their benefits, are distributed across an area. Despite an abundance of work evaluating access to trees and greenspaces, there is no standard tool for measuring this, and so it is difficult to compare access across locations. Many measurements rely on tree canopy cover but do not consider the spread and accessibility of trees across an area. The 3-30-300 rule offers a straightforward standard to examine access to trees and greenspaces and in addition to canopy cover, the distribution of trees around people’s homes, schools and workplaces is considered. The 3-30-300 rule is gaining popularity elsewhere in Europe, but not yet in the UK. We measure the 3-30-300 rule in the local authority areas of 7 English cities, examining how overall canopy cover and where the canopy is situated (e.g. woodland, street, private garden) impact success. This can be used to inform urban tree planning; ensuring that existing and newly planted trees are accessible and providing maximum benefits to the population. We also explore how sensitive the results of the 3-30-300 analysis are to several methodological choices. We compare a buffer method to a method using a network of walking routes for the ‘300’ rule and find that in each city region approximately twice as many buildings are within 300 m of a greenspace for the buffer method compared to the network analysis. Comparison of a buffer and a simulation of window lines of sight for the ‘3’ rule in the same regions shows that the fraction of buildings from which three trees are visible is reduced by around 10 % using lines of sight. These results indicate that methods should be chosen carefully to meet the desired outcomes of applying the 3-30-300 rule.