14 Nzokou et al.: Wood Residue Processing and Utilization in Southeastern Michigan tive value-added options. Clearly understanding these factors is critical to maximizing the economic value of these resources. The goal of this study was to assess the resource flow patterns for residue and green wood entering recy- cling yards and landfills in southeastern Michigan and to evaluate the potential for a better use of these resources. MATERIALS AND METHODS Survey Methods This study focused on 14 counties in southeastern Michigan (Fig- ure 1); these counties were also included in the wood residue gen- eration survey study conducted by Sherrill and MacFarlane (2007). A list of disposal yards and wood residue processing fa- cilities (in the study area) was compiled by using the Michi- gan Department of Natural Resources database, local tele- phone directory listings, and lists provided by the Southeast Michigan Resource Conservation and Development Council. Telephone calls were made to each company listed to en- sure that only those accepting wood residue were included. The corrected list for each county was forwarded County Directors of the Michigan State University Extension for validation, correction, and establishment of the final target population. A total 180 facilities were retained in the study. A questionnaire was developed to collect data on quantity and types of resources entering the yards, and amounts and value of products generated. The questionnaire was evaluated and pre- tested by wood use professionals to ensure clarity and suitability. Mailings, reminders, and follow-up calls were conducted from October 2007 to May 2008. In addition to categorical questions to obtain basic information about each company, questions were asked to identify the origin of woody material entering the yards, to characterize processing facilities, identify species processed and product types, and obtain total volumes produced in each fa- cility. Additional questions focused on current markets, market- ing strategies, and bottlenecks that prevent higher productivity. The average response rate for all counties was 23.3%, which is within range of typical response rates for survey studies of this type. A nonrespondent analysis was conducted by evaluating the geographical distribution, sizes, and characteristics of those who did not return the survey. The results indicated no noticeable dif- ferences between nonrespondents and respondents of the study. Companies were classified into types based on their size, equipment, processing capacity, and number of employees. Companies having at least three types of large equipment (in- cluding a chipper, stump grinder, chip van, or truck with dump bed) and at least 10 full-time employees were considered large processing facilities. All other respondents were classified as small processing facilities. Based on these criteria, 33% of the companies were classified as large, and 67% were small. Data collected from the respondents were extrapolated to determine first, the quantities of wood residue entering yards, and second, the types and volumes of products processed from these yards. This extrapolation was conducted through a method previous- ly used by Alderman et al. (1999) and Alderman et al. (2000). Field Methods Field studies of seven residue yards were conducted to validate mail-survey data, quantify inputs and yields, and identify poten- tial alternatives and bottlenecks. These companies were selected to reflect the diversity of products generated from disposal yards. A guided discussion was held with each owner or manager during the visits to obtain technical information about the yard size, total number of employees, major equipment, types of wood products/residues accepted, and products produced. No large disparity was observed between data from face-to-face in- terviews and mail-in surveys. Averages derived from the study were presented to yard owners and observed trends were dis- cussed and validated. Extended discussions were also conduct- ed to assess each owner or manager’s strategic vision for the future of wood residue processing in southeastern Michigan. RESULTS AND DISCUSSION Survey Data Characterization of wood waste processing facilities Figure 1. Michigan counties included in the study. Numbers in each county represent the response rate for the county. The aver- age response rate for the region was 23.3%. Adapted from U.S. Census Bureau, Census 2000 Map. ©2011 International Society of Arboriculture Respondents provided data that allowed the study authors to es- timate 1,082 full-time employees. The average number of em- ployees for a large yard was 7.5, while small yards averaged 4.8 (Table 1). The data also indicated that 78.5% of the large yards have their own field crews for tree removal and trim- ming operations, while only 31% of smaller yards had field crews (Table 1). The finding suggests that larger yards, by op- erating field crews that produce and collect their own wood residues, have a more reliable incoming base of wood re- sources, as compared to smaller yards, which had a tendency to depend more on drop-offs from other tree care companies. All facilities owned a combination of heavy-duty and light equipment, although the most common types of equipment var- ied between large and small operations (Table 2). The specific types of equipment typically found in the small yards clearly indicated their need to provide specialized, value-added ser- vices, such as delivering processed products, producing other products such as firewood, or creating solid wood products.
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