Arboriculture & Urban Forestry 33(1): January 2007 49 The total impact of the losses will include the loss in land- scape value, the costs of tree removal, including stumps where appropriate, and the cost of replacement trees (Council of Trees and Landscape Appraisers 2000). Loss in landscape value includes a variety of fiscal and environmental factors that are difficult to quantify such as increased heating and cooling costs, reduced property values, increased stormwater runoff, and reduced wildlife habitat as well as reduced aes- thetic quality. Note that we are not considering the tree’s timber value. Ash can be dangerous as a declining or dead tree and should be removed promptly to avoid tree or branch failures that can cause property damage or personal injury. Tree and stump removal are needed to prepare the site for a replacement tree. Sydnor et al. (2002) give guidelines for calculating replacement tree costs in Ohio. MATERIALS AND METHODS Ohio has 235 designated Tree City USA communities (Anonymous 2005), which work with Ohio’s regional urban foresters throughout the year. The state’s regional urban for- esters contacted some 200 of Ohio’s Tree Cities by mail or e-mail (whichever was available) to request their assistance in filling out the Ash Survey form, a simple one-page instru- ment with the questions listed in Table 1. The first request was made in October 2005 and a follow up with nonrespon- dents was made in November 2005. Some contact informa- tion was gathered but respondents were told that their re- sponse would be confidential. As promised, no individual responses are reported. Data were entered into a Microsoft Excel 2003 worksheet for analysis. To compare the response of a small community with the response of a larger community, it was decided to normalize the ash tree data by population. Street, park, and private tree numbers as reported by the communities were multiplied by the percentage of ash reported to get the num- ber of street, park, and private ash trees, which was then Table 1. Questions appearing on the survey instrument used in the study. No. 1 2 3 4 5 6 7 8 9 10 11 12 Question Population of your community. Estimated average household income of residents. Estimated number of properties in your community. Average age of commercial structures. Average age of residential structures. Estimated number of street trees. Percentage of street trees that are ash. Estimated average size of ash street trees. Estimated number of park trees. Percentage of park trees that are ash. Estimated number of trees on private property in community. Percentage of private trees that are ash. divided by the community’s population in thousands to give the number of street, park, and private trees per 1000 resi- dents. Communities were instructed to report only informa- tion they were comfortable in reporting, i.e., for which they at least had estimates. Reported data were entered to calculate all possible fields. Data are presented as means and medians with the number of category responses given. Estimated average size of ash street trees was reported by the communities as diameter at breast height (dbh) defined as 1.4 m (4.5 ft) above the ground. It was noted that some older communities had larger numbers of larger street trees and some younger communities had larger numbers of smaller trees. To account for this, a normalized dbh for street trees was computed. For each community, the reported average dbh for ash street trees was multiplied by the number of ash trees in that community, which was, in turn, divided by the total number of ash street trees reported by all communities. The total of all the communities gives the normalized average dbh. An initial evaluation identified some possible outliers in one or more fields. Representatives for the communities in question were contacted by telephone to enable us to further explore their responses. Various errors such as data entry errors were identified and corrected with the contact’s agree- ment. In other situations, the investigators got a feel for the complexion of that community’s urban forest and why the community gave the responses they did and the response remained as submitted. Still, outliers did create some skew in the data that resulted in differences between mean and me- dian values and are discussed later. It was anticipated that a community’s size and age might have an effect on the occurrence of ash trees. To test this proposition, the responding communities were split into two groups based on reported population. A population of 10,000 residents was used to separate the communities into smaller and larger categories. This number was chosen on inspection of the distribution of responding communities, which showed a natural break at this point. This figure also resulted in relatively even sizes between the two groups. Similarly, the communities were split into two age categories (younger and older) based on the reported average age of residential struc- tures. Again, on inspection of the distribution of responding communities, an average age of 60 years was used to divide the respondents. Comparisons were then made between the two groups using the nonparametric Wilcoxon rank sum test for the variables: ash street trees, park street trees, and private street trees (all per 1000 residents). A nonparametric test was chosen as a result of the relatively small sample sizes and skewness (positive) in the data. Tree removal costs were determined by contacting com- mercial arborists representing the five most populous metro- politan areas in Ohio. A total of seven arborists responded by giving prices for tree and stump removal in five tree size ©2007 International Society of Arboriculture
January 2007
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