346 Nowak et al.: Simple Street Tree Sampling Arboriculture & Urban Forestry 2015. 41(6): 346–354 David J. Nowak, Jeffrey T. Walton, James Baldwin, and Jerry Bond Simple Street Tree Sampling Abstract. Information on street trees is critical for management of this important resource. Sampling of street tree populations pro- vides an efficient means to obtain street tree population information. Long-term repeat measures of street tree samples supply additional information on street tree changes and can be used to report damages from catastrophic events. Analyses of several street tree popula- tions reveal that a 2%–3% sample of block segments with known length within a city will likely produce estimates on the total number of trees with a standard error around 10% of the total population estimate (relative standard error of 10%). Ratio estimates of number trees per length of street sampled reduced the number of block segments needed to attain a 10% relative standard error. Communities with a small tree population, or analyses of specific subsets of the population (e.g., individual species information), will likely need a higher proportion of block segments sampled to attain the same relative precision. This paper presents a simple means to sample street tree populations to aid in street tree management and presents information on how many block segments need to be sampled to achieve a desired sampling precision. Results can be used to develop simple, cost-efficient, and accurate means to sample street tree populations. Key Words. Block Sampling; Ratio Estimates; Sample Size; Street Trees. Understanding and quantifying the structure of the street tree resource (e.g., species composition, dbh distribution, health) is critical to basic street tree management. The most appropriate procedure to aid in street tree management is a comprehensive inventory (or census) of the street tree population. These inventories provide data on various tree char- acteristics and location that are essential to day- to-day management (e.g., Tate 1985; Smiley and Baker 1988). In cases where street tree inventories cannot be conducted (e.g., limited budgets), street tree sampling can provide a relatively inexpensive alternative for acquiring street tree data on overall street tree composition, health, and/or maintenance needs. However, street tree sampling does not pro- vide the essential data (e.g., comprehensive data on specific tree locations and conditions) that invento- ries can provide. Rather, sampling provides general overall statistics on the street tree population char- acteristics, such as species composition, tree sizes, health, and/or maintenance needs. Sampling can also provide a useful means to detect changes and essential information needed for budget planning. One of the goals of sampling is to produce a more precise estimate (e.g., number of trees) at minimal ©2015 International Society of Arboriculture cost. One way to assess precision is to compare the standard error (variability) of the estimate to the estimate itself. Dividing the standard error of an estimate by the estimate value produces a percent relative standard error (RSE). The lower the percent relative standard error, the higher the precision of the estimate. Increasing the sample size oſten increases precision, but sample design also affects precision. Various methods of street tree sampling have been reported in the literature. Mohai et al. (1978) and Valentine et al. (1978) describe a method that entails drawing approximately 50 to 100 random samples of streets with a length of two to three city blocks, and systematically sampling every xth tree of a species to produce a sample size of about 100 trees. This method can provide an efficient and accurate estimate of street tree populations, but requires information on species and population distribution such that sampling interval per species can be selected to reach a sample size of 100 trees. Jaenson et al. (1992) proposed a sampling method that stratifies the cities into zones and randomly samples blocks such that about 2,000 to 2,300 trees are sampled. This method can pro- vide accurate estimates of the street tree popula-
November 2015
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
