Allometric relationships of Betula populifolia in a naturally assembled urban woodlot

Background/Question/Methods: In an attempt to monetize carbon accumulation, regionalized metrics for afforestation offset projects have been developed.  Such a general approach is thought to be acceptable as the allometric relationships of many forest species have been fairly well documented.  However, forest carbon dynamics are not only a function of climate and edaphic conditions but also of stand history, and stress induced by abiotic filters such as disturbance, pests and soil contamination. These site-specific differences have been shown to result in corresponding growth difference. Therefore, we question if hetorgeneous edaphic conditions of a naturally assembled urban brownfield would result in allometric differences that could alter carbon sequestration rates. 

Results/Conclusions:

We measured the diameter at breast height and overall height for Betula populifolia within a 101.6 ha. urban brownfield in Jersey City New Jersey. Twenty eight individual trees, seven from four study sites each, were destructively sampled to determine allometric and mass relationships.  Predicted tree mass (TM) was estimated using a standardized major axis regression (SMA) calculated using the relationship between above ground biomass (g) and its DBH (mm).

Tree trunk taper, measured at 10 cm intervals for the three average trees from each of the four sites, was not found to vary by site. A positive OLS regression, pooled across sites, was identified for trunk taper.  Site conditions did not appear to impact the mass to diameter relationship within these trunk sections. However, the log-log SMA regression between branch mass and branch diameter indicates significant differences between sites. In addition, there was considerable variability in the tree growth parameters (DBH and height) between the four sites.