Plymouth Tree Canopy Cover Assessment

In February 2017, Treeconomics worked in collaboration with Forest Research to estimate tree canopy cover within the Plymouth Policy Area using the Bluesky National Tree Map dataset.

Estimates of canopy cover for each Ward in the Plymouth City Administrative Boundary, the Plymouth Urban Fringe and the total Plymouth Policy Area were calculated. The results provide a snapshot of the current tree canopy cover, and a baseline to allow for comparison with future tree canopy surveys. The study also compared tree canopy cover with relevant statistics from the Office for National Statistics (ONS) and reviewed other available sources of geographical data on human health, wellbeing and societal factors (such as crime rates, social deprivation and life expectancy) to observe if a correlation existed with tree canopy cover.

Canopy cover was compared with various quality of life indicators for Plymouth. For each indicator, Output Areas possessing less than 18% canopy cover, or more than 18% canopy cover were grouped for comparisons to be made.

Healthy Life Expectancy estimates the average number of years a person would live in ‘Very good’ or ‘Good’ health if he or she experienced the specified population’s particular age-specific mortality and health status for that time period throughout the rest of his or her life. Although overall life expectancy continues to rise, Plymouth has one of the widest healthy life expectancy gaps in the UK. There is a life expectancy difference of nearly 20 years between the west and east of the city. The results showed that in areas with higher tree canopy cover Healthy Life expectancy is increased, however other socioeconomic factors will also influence the result. For instance, in areas with more than 18% tree cover, the average healthy life expectancy stood at 63, compared to just 60 in areas with less than 18%. More ‘treed’ areas of Plymouth also had significantly fewer emergency hospital admissions.

Much of the data concerning deprivation was also collected in line with the Index of Multiple Deprivation (IMD). The IMD combines information from seven domains to produce an overall relative measure of deprivation. The domains were combined using the following weights: income deprivation (22.5%), employment deprivation (22.5%), education, skills and training deprivation (13.5%), health deprivation and disability (13.5%), crime (9.3%), barriers to housing and services (9.3%), and living environment deprivation (9.3%).

Crime statistics, as a measure of the risk of personal and material victimisation at the local level, were also accounted for in the comparative analysis. Though still ranked as below average on a national scale, Plymouth has the highest crime rate in the Devon and Cornwall area with 68.93 crimes per 1000 residents, compared to an average of 46.53.  Nonetheless, there is a wide variation between areas like Plympton and Chaddlewood (circa 100 crimes and 14% tree cover) and Sutton and Mount Gould (circa 500+ crimes and 3% tree cover).

Generally, across the Plymouth Policy Area, areas with higher tree cover also have lower crime rates. Increasing tree cover would be one way to create safe and accessible environments, which are also visually attractive. Although poorly maintained areas can increase the perception of crime, studies in the US have demonstrated that a 10% increase in tree cover equaled a 12% reduction in crime. Furthermore, among minor crimes, there is less graffiti, vandalism, and littering in outdoor spaces with natural landscapes than in comparably plant-less spaces.

Data collected in this study can now inform where there are opportunities to increase tree cover by highlighting areas of low tree canopy cover and the available plantable space within them. Planting could also be specifically targeted to the areas which are the most deprived. This report highlights much scientific research that supports the assertion that trees provide a wide range of valuable ecosystem services. Plymouth as a whole has 18% tree canopy cover, but within many of the most deprived areas the canopy cover is much lower, and so too is the value of ecosystem services provided. Increasing Tree Cover in Plymouth will provide multiple benefits to the community, and should be part of the solution in creating resilient places for people to live and work.