Allometric and mass relationships of Betula populifolia Marsh. in a naturally assembled urban brownfield: Implications for carbon modeling

Background/Question/Methods: While predictive models for the sequestration of carbon by forests have been in development since the mid 1990’s, recent attempts to monetize carbon accumulation have led to the development of regionalized metrics for afforestation offset projects. However, aboveground forest carbon sequestration is known to be a function of allometric relationships, stand history, and edaphic conditions. We investigate how the heterogeneous edaphic conditions of a naturally assembled urban brownfield influence the allometric relationships of the dominant species Betula populifolia. We measured diameter at breast height (DBH), height, mass and age on four sites that exhibited considerable edaphic differences. Since it had been demonstrated that productivity, as measured by both the Normalized Difference Vegetative Index and tree ring growth, of B. populifolia within this urban forest stand could be affected by soil metal induced stress we expected that such differences might also lead to inconsistent allometric relationships and therefore differences in carbon sequestration estimates.

Results/Conclusions: While this study indicates that there were differences within several allometric relationships of Betula populifolia within this urban forest, overall trends in biomass/DBH relationships were consistent across the site. Apparently the slight differences in branch biomass, is insignificant when comparing cumulative aboveground tree mass. However, resource allocation between growth and maintenance within the heterogeneous edaphic conditions of the urban context clearly results in considerably different growth rates and stocking densities, which could have significant impacts on C models for urban areas.