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

Abstract

Many studies have analyzed the benefits, costs, and carbon storage capacity associated with urban trees. These studies have been limited by a lack of research on urban tree biomass, such that estimates of carbon storage in urban systems have relied upon allometric relationships developed in traditional forests. As urbanization increases globally, it is becoming important to more accurately evaluate carbon dynamics in these systems. Our goal was to understand the variability and range of potential error associated with using allometric relationships developed outside of urban environments. We compared biomass predictions from allometric relationships developed for urban trees in Fort Collins, Colorado to predictions from allometric equations from traditional forests, at both the individual species level and entire communities. A few of the equations from the literature predicted similar biomass to the urbanbased predictions, but the range in variability for individual trees was over 300%. This variability declined at increasingly coarse scales, reaching as low as 60% for a street tree community containing 11 tree species and 10, 551 trees. When comparing biomass estimates between cities that implement various allometric relationships, we found that differences could be a function of variability rather than urban forest structure and function. Standardizing the methodology and implementing averaged equations across cities could be one potential solution to reducing variability; however, more accurate quantification of biomass and carbon storage in urban forests may depend on development of allometric relationships specifically for urban trees.Urban Ecosyst (2009) 12:95-113

Assessing urban tree carbon storage and sequestration in Bolzano, Italy

“…However, due to local regulations, liability, and public perceptions and safety, destructive sampling is expensive and difficult in an urban environment. Although McHale et al (2009) found that some of these allometric equations for forestgrown trees yield similar biomass estimates for urbangrown trees; these allometric equations can produce very different results when applied to sites outside the region where the equations were originally developed (ZapataCuartas et al 2012).…”

“…According to Jo and McPherson (1995), McHale et al (2009), andYoon et al (2013) the use of allometric biomass equations based on forest-grown trees can overestimate or underestimate urban tree biomass. For example an urban tree with the same DBH or height as a forest trees could have a different biomass due to the conditions of the urban environment relative to forest-grown trees (Jo & McPherson 1995).…”

“…Therefore, a modern approach to estimate urban tree heights and increments is using Light Detection and Ranging (LiDAR) data (Shrestha & Wynne 2012;Ramdani 2013). LiDAR data can be also used for estimating urban tree volume that can then be converted to biomass using specific gravity values for individual tree species (McHale et al 2009). …”

“…However, due to local regulations, liability, and public perceptions and safety, destructive sampling is expensive and difficult in an urban environment. Although McHale et al (2009) found that some of these allometric equations for forestgrown trees yield similar biomass estimates for urbangrown trees; these allometric equations can produce very different results when applied to sites outside the region where the equations were originally developed (ZapataCuartas et al 2012).Therefore, since the Eco/UFORE and CTCC models use North American equations and this study was conducted in Europe, we used site-specific tree species, tree dendrometrics such as stem circumference (subsequently converted to diameter), and height data and applied mostly European-specific allometric equations derived from the literature (Appendix 1) to better approximate local urban tree C storage estimates. The equations in Appendix 1 were used specifically to calculate dry weight aboveground biomass of each measured tree and not total dry weight biomass due to the complexity in estimating the belowground portion as reported by Hutyra et al (2011) and Strohbach and Haase (2012).…”

Above ground biomass and leaf area models based on a non destructive method for urban trees of two communes in Central Chile

“…Also the variables that affect urban tree growth (i.e. soil, water, solar resources) are different among cities, therefore allometric relationships within those urban trees vary (McHale et al 2009). …”