Urban tree specific gravity and ash content: A case study from Baltimore, Maryland USA
Interest in conducting urban tree inventories and quantifying the associated wood resource has accelerated at a pace faster than supporting research needs can be identified and accomplished. For example, it is common to apply allometric models and wood properties values developed from studies of rural forest-grown trees to urban trees, despite unknown degrees of inaccuracy that may exist. To examine potential differences in wood properties between trees grown in forest and urban settings, wood samples were collected from stumps of recently felled trees for nine native hardwood species in the city of Baltimore, MD USA. The samples were analyzed for basic specific gravity (SG) and ash content (AC). The results from urban trees were compared with published values from studies based on forest-grown trees. There was no general trend in the results for SG; however, urban Acer rubrum L., Fraxinus spp., and Quercus rubra L. appeared to have higher SG, with Quercus palustris Münchh. having lower SG, than their forested counterparts. Based on these results, the use of existing forest-based SG data may produce weight estimates of urban woody biomass that are 5–10% too low. Conversely, most of the species studied exhibited higher AC than their forested counterparts, although some results were mixed depending on the basis of comparison. Further work is needed on a wider range of species and geographic locations to refine the results and better support the analysis of urban tree inventories, which are increasingly used for carbon accounting and assessing feedstocks for biofuel use.