Street Trees as a Source of Timber in Washington, DC

Abstract

Recycling felled urban trees that are hazardous or unhealthy is increasingly viewed as a viable practice to control disposal costs, promote environmental practices, and support local commerce. Wide spread waste wood utilization is encumbered by numerous presumptions about wood quantity, quality, accessibility, and presence of foreign objects; yet there is almost no scientific literature about these presumptions. Without this knowledge, informed decisions cannot be made about the viability of waste wood utilization. In this study, we assessed the quality and quantity of timber in street trees scheduled for routine removal by the District of Columbia (the District) using a modified timber grading protocol adapted from the United States Forest Service. We developed a second protocol to assess the feasibility of timber salvage by identifying physical barriers commonly encountered in urban areas (e.g., high volume traffic, utilities around the tree, and infrastructure). The randomized sampling scheme was stratified by land-use zones and focused on the six most abundant tree species: Acer platanoides, Acer rubrum, Acer saccharum, Quercus palustris, Quercus phellos, Quercus rubra. Our findings suggest the majority of condemned street trees are of too poor quality to contain timber (58% cull rate); however, trees that contain merchantable logs are likely to be easily removed. A notable discovery that could prove problematic for wood salvage was that the majority of trees (88%) contained superficial metal items embedded in the trunk surface. Furthermore, presence or absence of a merchantable-sized log (p=0.0445) depended on the tree's species, as did the average volume observed (p<0.0001). Additionally, land-use zones had an effect on the removal feasibility scores (p=0.0257) but had no effect on log presence or log volume. Throughout the District, we estimated that 36,500 board feet of merchantable logs are generated from routine removals of our top six species annually. These findings provide empirical data pertaining to urban timber salvage, which might aid decisions on the investment worthiness of utilizing urban street trees.