Arboriculture & Urban Forestry 44(2): March 2018 ute to statistical differences between volunteer- collected and professionally collected data. However, when using comparable equipment, relatively small differences in levels of agreement occurred, which suggests volunteers can reliably collect accurate and useful data when provided with adequate tools (Nicholson et al. 2002). Data quality, based on practical levels of agree- ment over statistical significance, is an impor- tant consideration when including community volunteers in the resource management process. Previous studies have shown that even certified, professional arborists can differ significantly from one another in their assessment of taxo- nomic identification, tree condition (Bloniarz and Ryan 1996), and tree appraisals (Ponce-Donoso et al. 2017). Statistically significant differences in measurement of tree crown metrics and trunk diameter have been reported for professionals, although the differences were typically under 2.54 cm for DBH measurements (McRoberts et al. 1994; Elzinga et al. 2005). In an examination of volunteer accuracy for street tree inventories across two different communities in suburban Boston, an 80% agreement level between street- tree data collected by volunteers and certified arborists was used as a reasonable threshold for agreement (Bloniarz and Ryan 1996). As varia- tions in measurements among professionals is not uncommon, determining an acceptable value of variation or agreement in measure- ment will depend on management objectives. Historically, the validity and usefulness of volunteer-collected data for use in natural resource management has been a common con- cern and source of scrutiny. As government agen- cies increasingly look to volunteer-generated data to support monitoring and management programs, quality of data is cited as a source of major concern among regulatory bodies and sci- entists (Penrose and Call 1995). This critique is primarily attributable to a lack of understand- ing regarding the potential for error, or bias, of volunteer-collected data (Dickinson et al. 2010). While the existing literature provides evi- dence that trained volunteers can effectively col- lect monitoring and assessment data across a range of natural resource disciplines, research on the use of volunteers, as part of urban forest 75 inventory or survey initiatives, is minimal. The first objective of this study was to determine the level of agreement between trained volunteers and experienced university researchers for dif- ferent urban forest inventory tasks (i.e., species identification, tree measurements, and condi- tion-rating). The second objective of this study was to determine the effect training method had on the probability of agreement between volunteer-collected and researcher-collected data. MATERIALS AND METHODS In 2009, six Minnesota communities were selected to participate in an emerald ash borer Rapid Response and Community Preparedness grant to assess the vulnerability of their urban forests to emerald ash borer infestations. Eight additional communities were selected in par- ticipate in 2011 and 2012. Communities were selected based on population, capacity to man- age their urban forest, and location in the four primary ecological provinces as defined in the Minnesota Department of Natural Resources and the U.S. Forest Service Ecological Classifica- tion System (Minnesota Department of Natural Resources 2016). The first group of communi- ties included: Crookston, Hendricks, Hibbing, Hutchinson, Morris, and Rochester. The second group included: Brainerd, Bemidji, Ely, Mankato, Mora, Royalton, Saint Cloud, and Starbuck. The fourteen Minnesota communities took part in volunteer-led tree surveys or inventories to count, identify, and measure both publicly- and privately-owned community trees, and condition rate trees in public spaces. In each community, areas were selected using an urban street tree rapid-sampling protocol (Jaenson et al. 1992). Surveys of the sample areas were com- pleted by community volunteers. The communi- ties of Starbuck and Hendricks each completed a full inventory due to their small size. Volun- teers were recruited through press releases in community newspapers, and solicitation of Min- nesota Master Naturalists, Minnesota Master Gardeners, and Minnesota Tree Care Advocates through email lists. Volunteers ranged in age from 18 to 75, in level of education completed from some high school to doctorate, and in expe- rience working with natural resources from no ©2018 International Society of Arboriculture
March 2018
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