Arboriculture & Urban Forestry 41(4): July 2015 Arboriculture & Urban Forestry 2015. 41(4): 223–229 223 Determination of Crew Size Efficiency Relative to Urban Tree Inventories Arthur H. Chappelka, Edward F. Loewenstein, Greg L. Somers, Gary J. Keever, and Nicholas A. Martin Abstract. Trees on the campus of Auburn University (Auburn, Alabama, U.S.) were used to test the efficiency of different crew sizes in conducting a 100% tree inventory. Seventy trees were randomly sampled at-large from a previously conducted 100% inventory (7,345 trees) on the Auburn University campus. Different crews consisting of one, two, or three individuals collected and recorded data using a GPS unit that timestamped the initiation and completion of data collection for each tree. The average time spent per tree was then calculated. Crews visited separate trees each time so there would be no overlap or bias. Each tree sampled was visited by all three crew sizes at different times. The relationship of sampling time per tree with increasing tree dbh was determined using regres- sion analysis and subsequently likelihood ratio F tests. There was no statistical difference in the interval required to inventory a tree as dbh approached 0 (intercept, fixed time) for a two- and three-person crew, but the set-up (fixed) time for a one-person crew was significantly greater (approx. 2×) irrespective of dbh. The time interval it takes to inventory each tree increased with increasing dbh; however, the rate of change was significantly less for a three-person crew compared with the other crew sizes. Based on these results, the number and relative sizes (dbh) of trees to be inventoried must be considered when determining optimal crew size. Key Words. Alabama; Chinese Elm; Crew Size; i-Tree Eco; Loblolly Pine; Pinus taeda; Quercus phellos; Sampling Efficiency; Tree Inven- tory; Ulmus parvifolia; Urban Forest Sampling; Willow Oak. Urban forests are ever-changing landscapes char- acterized by the presence of trees, other vegetation, and humans and their developments. To accurately access the urban forest and associated ecosystem services one needs to be aware of the forest’s com- position, health, and structure. Tree inventories are conducted and analyzed to provide this informa- tion, which then can be used for planning purposes and prioritization of tree maintenance needs (Tate 1985; Nowak et al. 2008). In conducting inventories, one important factor is resource (e.g., money, labor) availability (Massey et al. 1979; Smiley and Baker 1988). The cost to complete an inventory is deter- mined by several aspects, including sampling area, the amount and type of data collected, and inventory personnel. The size of the crew to be used is very important in this regard. For example, is a one-person crew more efficient than a two- or three-person crew? Nowak et al. (2008) determined that a two-person field crew using the i-Tree protocol (i-Tree 2010a; i-Tree 2010b; i-Tree 2010c) can collect data from 200, 0.04 ha plots in approximately 14 weeks. Martin et al. (2011a), as part of a larger study using a i-Tree Eco to conduct a 100% inventory on the Auburn University campus (Martin et al. 2011b), ascertained that a one-person crew was relatively more efficient than a three-person crew in data collection. A two- person crew was found to be the most efficient based on time of data collection on a per tree basis. How- ever, these data were collected as a small part of the overall study which was not designed to specifically test the efficiency of crew size (i-Tree 2010a; i-Tree 2010b; i-Tree 2010c). In addition, the majority of trees on the campus sampled by the one-person crew were <25.4 cm in diameter. Based on these limitations, it was difficult to accurately extrapolate the data to sites with predominately larger trees. The purpose of the current investigation was to expand on the study by Martin et al. (2011b), by determining the efficiency of crew size in urban tree inventories across a wide range of tree sizes. Urban forest inventory and sampling techniques ©2015 International Society of Arboriculture
July 2015
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