Arboriculture & Urban Forestry 33(4): July 2007 Arboriculture & Urban Forestry 2007. 33(4):253–263. 253 Quantifying Urban Saw Timber Abundance and Quality in Southeastern Lower Michigan, U.S. David W. MacFarlane Abstract. There is a growing need for society to use resources efficiently, including effective use of dead and dying trees in urban areas. Harvesting saw timber from urban trees is a high-end use, but currently, much urban wood ends up in landfills or is used for wood chips or biomass fuel. To assess the general feasibility of harvesting urban wood, a regional estimate of urban saw timber quantity, quality, and availability was developed for a 13-county area in southeastern lower Michigan, U.S. Conservatively, over 16,000 m3 (560,000 ft3 ) of urban saw timber is estimated to become available each year in the study area from dead and dying trees, enough to supply the minimum annual needs of five small sawmills. The quality of wood in urban softwoods was generally low but comprised only a relatively small portion (10%) of urban wood. Wood quality of urban-grown hardwoods was comparable to that found in forests in the region, although the absolute volume was nine times less. Although there are potential concerns with harvesting urban trees for saw timber such as low availability and poor wood quality, the results of this study suggest that many of them may be unfounded. Key Words. Saw timber; urban forestry; wood products; wood recycling. The value of trees in urban areas has been given considerable attention, in particular for improving aesthetics, environmen- tal quality (McPherson et al. 1999), and property values (Scott and Betters 2000). For example, recent studies have highlighted the significant contribution of urban trees to car- bon sequestration (Johnson and Gerhold 2001; Nowak and Crane 2002). The wood products potential of urban trees is typically not fully realized (Bratkovich 2001; Solid Waste Association of North America 2002; Sherrill 2003), although it is sometimes among the listed values for them (Scott and Betters 2000), often because of a perceived lack of quality wood in urban trees, logistical issues associated with harvest- ing commercial wood that may make it economically unat- tractive or infeasible, and an associated lack of social infra- structure geared toward using or recycling urban wood. The perceived lack of value for urban trees comes from legitimate concerns about foreign objects in urban trees such as nails, stone, or even signage (Sherrill 2003). However, the advent of portable sawmills with inexpensive and easy-to- change blades (e.g., Wood-Mizer, Wood-Mizer Products Inc., Indianapolis, IN; Bratkovich 2001) as well as routine metal detection equipment on sawmill feed lines (Kerry Mur- phy, Weyerhauser Inc., pers. comm.) greatly reduces the im- pact of foreign objects in urban tree wood. Wood quality is also an important issue, however. Many urban trees are not growing under optimal conditions for saw timber production attributable to stressful site conditions and exhibit an open growth form that promotes short bole lengths and large branch knots that reduce wood quality (DeBell et al. 1994; Uusitalo and Isotalo 2005). The main logistical problem for harvesting urban wood is that it primarily becomes available through the random death of trees and is only in abundant supply through catastrophic mortality events, e.g., the recent large-scale mortality of ur- ban trees caused by exotic, invasive tree pests, including em- erald ash borer (Agrilus plannipennis) (Poland and McCul- lough 2006) and Asian longhorned beetle (Anoplophora gla- bripennis) (Nowak et al. 2001). Other logistical concerns relate to the accessibility of urban trees for commercial har- vest, because they may have to be cut into small sections to be removed safely; felling urban trees in log lengths may create excessive liability attributable to nearby hazards (but see Sherrill 2003 for suggestions on efficient and safe re- moval). Recent studies by Bratkovich (2001) and Sherrill (2003) have compiled evidence suggesting that harvesting urban saw timber is not only feasible, but may also be profitable. How- ever, no previous study has systematically estimated both the potential availability and quality of urban saw timber over a geographic region. Without specific information regarding wood quality and availability, it is difficult to generalize about the potential for harvesting saw timber from urban trees. The goal of this study was to quantify the abundance, quality, and accessibility of urban saw timber in southeastern ©2007 International Society of Arboriculture
July 2007
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