Allometric relationships for urban trees in Great Britain

Tree allometry describes the relationship between tree biometric variables, such as tree diameter (at breast height, DBH), height and crown width and helps urban foresters to assess many of the economic and ecological benefits provided by trees of different size. However, there is little knowledge on how the relationships established between those variables change between trees from different urban areas or species, especially within Great Britain (GB). This study aims to evaluate the variation in the allometric relationships of seven tree species growing in eight GB urban areas, and to understand if the use of generic curves representing relationships of trees growing across all locations is adequate. The variation between locations was highly significant; nevertheless, mean relationships of young trees growing in different locations were still accurately represented by a common species curve. Species with a similar stature also showed significant differences in their mean allometric relationships, reducing the level of accuracy when estimating mean relationships with multiple-species curves. Findings also suggest that crown width could be correctly predicted from DBH measurements. This knowledge can be used in citizen science based surveys, where the measurement of crown width is required but often challenging.