Arboriculture & Urban Forestry 42(6): November 2016 and efforts put underway to gain the permission of these cities to use their data for a pilot study that could help elucidate important variables for a long-term, multi-location cohort study. Proposed Study 2: Multi-location Cohort Study Long-term health and longevity studies can be designed (e.g., cohort) or observational (e.g., retroactive study). The six-community study pre- viously described is similar to a retroactive epi- demiological study on human health (Ahrens et al. 2014). In addition to epidemiology, medical researchers and public policy analysts (mind- ful of many of the issues noted here) sometimes design and conduct long-term cohort studies to test the impacts of various treatments, behav- iors, or external factors on a group of subjects over time. This allows the researchers to truly standardize data collection and even prescribe “interventions” (e.g., a stress management pro- gram) to a subset of the sample populations. A long-term cohort study of the impacts of tree maintenance on tree longevity and condi- tion would allow more control over the species included, maintenance conducted, and measure- ments taken. Still, there are some significant logistical considerations associated with such an undertaking. Working with a single location would be the easiest approach; however, find- ings may be limited to that city or cities with similar environmental and socio-cultural grow- ing conditions, species profiles, source nurseries and planting stock, and management objectives. Working with multiple sites would require some cities to modify their existing inventories and perhaps their tree planting and care practices (unless the sites chosen have a similar inventory and maintenance contractor, like the six cities from the retroactive study in California). Beyond data, the tree work conducted would need to be standardized via thorough and understandable specification of arboricultural practices. Finally, the sites would need to have a significant plant- ing program (or the ability to coordinate one) to provide the necessary sample size. For a cohort study to be successful, the trees included would need to be studied over their whole life span, from planting to removal. Starting with a group of trees 385 already present may yield a biased sample, as the trees have all survived the stress of transplanting. While noting the challenges associated with a conducting long-term, multi-site cohort study (e.g., cost, standardization of data collec- tion, commitment of all individuals and groups involved), many in the panel believed the ben- efits offered by this approach warranted fur- ther investigation. While trained arborists and urban foresters may maintain trees according to industry standards and best management practices, there is often limited research show- ing this work improves tree health and survival over the long term. Unless a robust, long-term assessment is conducted, urban forest managers and arborists can only infer that practices tested through short-term assessments will result in greater urban tree growth and longevity. Several members within the expert panel leſt the summit committed to pursuing this cohort research question further. Many cities like Mil- waukee, Wisconsin, U.S. (Koeser et al. 2013; Sivyer 2015) and New York City, New York, U.S. (Lu et al. 2010; Barrick 2015) have proactive inven- torying, planting, and management programs. The urban foresters present at the summit noted it would not be difficult to adjust inventory- ing parameters/methods to a more standardized format. Others noted that efforts were already underway to standardize urban tree inventory data collection though an initiative led by the Arboricultural Research and Education Academy Urban Tree Growth and Longevity working group (Leibowitz 2012; McPherson and Roman 2012). Using the findings from the retroactive study proposed herein (and others) as pre-proposal data, the group intends to pursue larger fund- ing sources (e.g., National Science Foundation, European Union) to establish an array of urban forest long-term social-ecological observatories to track the long-term benefits and costs of tree care over time (e.g., reduced service calls, increased property value, avoided maintenance costs over time). These sites would be cities with an exist- ing commitment to urban forestry that have ties to research institutions (e.g., research centers, universities, arboretums). While this would likely limit the sample to sites with more actively man- aged urban forests, the participating cities would ©2016 International Society of Arboriculture
November 2016
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