Methodology

Thirty trees species common to UK towns were categorised by stature: small, medium, large^1,2, and leaf type: conifer, broadleaf. For each species, tree size was estimated over a 100 year period using growth rates from the literature averaged for each stature and leaf type.

A tree’s total carbon storage, gross annual carbon sequestration, annual avoided stormwater runoff and annual air pollution removal contributions were estimated using i-Tree Eco³ for each species over 100 years. Trees were modelled in three location types: open (no over shading), semi-open (over shadowing on 2 sides) and enclosed (overshadowing on each side and from above) by using the i-Tree Eco Crown Light Exposure values of 5, 3 and 1, respectively.

Amenity value of trees was estimated using the CAVAT full method⁴.

Lifespan was assumed to be 80 years for small stature trees, 150 years for medium stature, and over 200 years for large stature. Trees were estimated to be planted at age seven, with a one-year lag (no growth) phase post-planting.

Ecosystem service values were normalised to aid comparison: with a maximum value of 1 and minimum value of 0.

Assumptions

Ecosystem service provision by any one tree will be influenced by its regional climate, location, health, growth rate and lifespan.

Trees were modelled in the same region, land-use type and under constant condition levels to ensure comparability; benefit provision is, therefore indicative, only.

This work only considers four ecosystem services; urban trees also provide a wide range of other benefits including cultural, wellbeing and biodiversity services⁵.

Growth of trees is modelled based on average growth rates for their stature group. Species may have faster or slower growth rates, which would affect their ecosystem service provision.

References

1. Hand, K., Doick, K. & Moss, J. (2019). Ecosystem services delivery by small and medium stature urban trees. Forest Research.
2. Hand, K. L., Doick, K. J. & Moss, J. L. (2019). Ecosystem services delivery by large stature urban trees. Forest Research.
3. Nowak, D. J., Crane, D. E., Stevens, J. C., Hoehn, R. E., Walton, J. T., & Bond, J. (2008). A Ground-Based Method of Assessing Urban Forest Structure and Ecosystem Services. Arboriculture & Urban Forestry, 34, 347–358.
4. Doick, K. J., Neilan, C., Jones, G., Allison, A., McDermott, I., Tipping, A. & Haw, R. (2018). CAVAT (Capital Asset Value for Amenity Trees): valuing amenity trees as public assets. Arboricultural Journal, 40, 67–91.
5. Davies, H. J., Doick, K., Handley, P., O’Brien, L. & Wilson, J. (2017). Delivery of ecosystem services by urban forests. Forestry Commission.

More Resources

Information presented on this page complements guidance including the Urban Tree Manual, TDAG’s guide to urban tree species, and the Forestry Commission's Right Trees for a Changing Climate and should be used in conjunction with these resources.

Barbook, J., Mackenzie, R., Doick, K. J., Griffiths, A., Salisbury, A. & Smith, J. C. (2018) Urban tree manual. Forest Research.

Britt, C. & Johnston, M. Trees in Towns II. A new survey of urban trees in England and their condition and management. (Department for Communities and Local Government, 2008).

Forestry Commission. Right trees for a changing climate. Available at: http://www.righttrees4cc.org.uk/. 

Gilbertson, P. & Bradshaw, A. D. (1990). The survival of newly planted trees in inner cities. Arboricultural Journal, 14, 287–309.

Hirons, A. & Sjöman, H. (2019). Tree Species selection for Green Infrastructure. A guide for Specifiers. Trees & Design Action Group.

Smith, J. (2021). The Mayor’s Street Tree Programme Final Evaluation Report. Forestry Commission for Mayor of London.

Vaz Monteiro, M., Handley, P. & Doick, K. J. (2019). An insight to the current state and sustainability of urban forests across Great Britain based on i-Tree Eco surveys. Forestry, 1–17.