Assessing above-ground biomass of open-grown urban trees: A comparison between existing models and a volume-based approach

- Performance of two forest-derived allometric biomass models was tested for urban roadside trees.
- The stem and branch biomass estimates from the allometric models contained significant errors.
- Especially branch biomass was heavily underestimated.
- A TLS-based method was developed and tested for estimating stem biomass.
- The developed TLS-based method outperformed the existing allometric models in estimating stem biomass.

Assessment of the amount of carbon sequestered and the value of ecosystem services provided by urban trees requires reliable data. Predicting the proportions and allometric relationships of individual urban trees with models developed for trees in rural forests may result in significant errors in biomass calculations. To better understand the differences in biomass accumulation and allocation between urban and rural trees, two existing biomass models for silver birch (Betula pendula Roth) were tested for their performance in assessing the above-ground biomass (AGB) of 12 urban trees. In addition, the performance of a volume-based method utilizing accurate terrestrial laser scanning (TLS) data and stem density was evaluated in assessing urban tree AGB. Both tested models underestimated the total AGB of single trees, which was mainly due to a substantial underestimation of branch biomass. The volume-based method produced the most accurate estimates of stem biomass. The results suggest that biomass models originally based on sample trees from rural forests should not be used for urban, open-grown trees, and that volume-based methods utilizing TLS data are a promising alternative for non-destructive assessment of urban tree AGB.