90 Hauer et al.: A Volunteer and Partnership Baseline for Municipal Forestry Activity in the U.S. was sent to locations where an e-mail was available. A sixth mailing with a replacement short version of the questionnaire was sent. A total of 667 com- munities (38.6%) responded, and this was slightly higher than two previous municipal tree care sur- veys in 1986 (38.1%), by Kielbaso et al. (1988), and in 1993 (34.1%), by Tschantz and Sacamano (1994). The Institutional Review Board associated with this study was involved to approve the proto- col for the study. No non-respondent bias was dis- cerned in this study as determined by comparing results from this study with equivalent published results. For example, the total volunteer hours reported in this study were consistent with results collected by the United States Department of Agriculture Forest Service (USDA-FS) Urban and Community Forestry Program in the study year. Statistical Approach Each research question was craſted a priori to implementation of the study analysis. These ques- tions included: 1) What volunteer capacity oc- curred in municipal forestry in 2014 (e.g., total number, total hours, full-time equivalents, mean time per person)? 2) What activity areas do vol- unteers participate in (e.g., tree boards, tree main- tenance types, advocacy, fundraising, policy), and if training is provided? 3) What organizations were involved with community tree management partnerships (e.g., individual residents, civic or- ganizations, neighborhood associations, business associations, school groups/youth organizations, nonprofit groups, municipal governance group, and utilities)? These three questions were further disag- gregated by population (group) of communities. The fourth question ascertained if commu- nity strength of their urban forestry program was related to volunteer incorporation into municipal forestry activity. Each community was given an index score using a model of urban forestry sus- tainability (Clark et al. 1997). A total 19 of 20 index areas were used, each with a 1 to 4 score possible, with a composite index score ranking between 19 and 76. The native vegetation criteria in the vegetation resource component was unable to be ascertained in this study. The composite index score was derived from summing the three com- ponent (category) groups that relate to resource management, community framework, and veg- etation resource criteria (Clark et al. 1997). The index score was used to test the hypothesis that more advanced programs (interpreted as a higher index score) were more likely to incorporate vol- unteers (Ha: Programs with greater score more likely to incorporate volunteers). ANOVA were performed to compare communities on number of volunteers used, amount of volunteer hours used, and urban forestry sustainability index score. As a test, if volunteers were a replacement for a munici- pal forestry program, χ2 analysis was further used to ascertain if communities that did not conduct public tree activity were more likely to incorpo- rate volunteers. An α ≤ 0.05 significance level was used to detect a difference for both statistical tests. The fiſth research question identified if attributes of a municipal forestry program explained if a com- munity engages volunteers. Logistic regression was used to model whether a community involved vol- unteers in urban forest/tree management activities against seventeen predictors (Table 1). Initial pre- liminary models used an α ≤ 0.25 significance level to determine if a variable potentially explained volunteer inclusion. Through subsequent model refinements, the best model was selected based on the significance of individual predictors and the Akaike information criteria (AIC) value of the models (Hosmer et al. 2013). Researchers also used the ANOVA function (glm) in R (version 3.3.1) to compare nested models. Overall significance of the model was tested using χ2 goodness-of-fit test (Hosmer et al. 2013); researchers also used residual plot (both Pearson and deviance) to examine model fit (Hosmer et al. 2013). Researchers also used receiver operating curve (ROC) and area under ROC to evaluate model fit (Hosmer et al. 2013). Finally, a combination of backward and forward selection procedures were then used to examine the best model, and to determine if initially excluded variables provided explanation as interpreted with an α ≤ 0.05 significance level, with no pre- viously excluded variables found to be significant. RESULTS Communities in the United States commonly in- corporated volunteers and informal partnerships with organizations into municipal tree activities ©2018 International Society of Arboriculture
March 2018
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