Urban forest biomass estimates: Is it important to use allometric relationships developed specifically for urban trees?

Estimates of carbon storage in urban trees have generally been based on allometric equations developed for traditional forests. There is debate, however, about whether this is appropriate considering differences in the way trees grow under urban vs forest conditions. This study compared the carbon storage values for trees in Ft. Collins, CO, calculated using forest equations and newly developed equations based on measured urban trees. A nondestructive method using LiDAR was used to measure the total tree volume of 14-22 trees of the 11 most common species in the city. From this data, new equations relating DBH to volume were derived. These equations were then used to estimate the carbon storage of all trees of the 11 species in Ft. Collins’ street tree inventory. Forest equations that have been used in urban forestry studies [particularly in the STRATUM and UFORE software tools (now known as i-Tree Streets and i-Tree Eco, respectively)] were used to estimate the carbon storage of the same trees. Results of the two groups of equations varied widely (up to 205% for individual trees, up to 109% for populations within a species, and up to 40% at the community level). The study methodology did not allow a determination of which method is more accurate.