56 Martin et al.: Evaluation of Sampling Protocol for i-Tree Eco Arboriculture & Urban Forestry 2013. 39(2): 56–61 Evaluation of Sampling Protocol for i-Tree Eco: A Case Study in Predicting Ecosystem Services at Auburn University Nicholas A. Martin, Arthur H. Chappelka, Greg Somers, Edward F. Loewenstein, and Gary J. Keever Abstract. Auburn University (Auburn, Alabama, U.S.) was used as a site for a case study evaluating the standard plot sampling protocol for i-Tree Eco. A 100% tree inventory of the managed areas of campus was conducted in 2009–2010 and provided a complete data set for the eval- uation. Air pollution removal, carbon storage, and carbon sequestration were the ecosystem services examined. Total tree population was also utilized for this assessment to provide a comparison to i-Tree Eco protocol. To achieve an estimate with a ±10% allowable error of the total cam- pus value, 622 plots (0.04 ha each) with at least one tree present would need to be inventoried for air pollution removal, 870 plots for carbon storage, 483 plots for carbon sequestration, and 258 plots for number of trees, as opposed to the standard i-Tree Eco protocol of 200 plots. This study provides a first step in evaluating i-Tree Eco sampling protocol; however, efforts testing these results at sites throughout the south- ern United States are needed to provide the most accurate estimate of plot numbers necessary for predicting ecosystem services of urban forests. Key Words. Alabama, i-Tree Eco; Plot Sampling; UFORE Model; Urban Tree Inventory. In the current urban environment, transformations take place every day, many of which impact the urban forest. It is critical for urban forest managers to recognize these changes and their impacts, and be able to evaluate them in the future. Tree inven- tories are conducted and analyzed to provide information regard- ing urban forest structure and function, to support urban forest resource management and to evaluate environmental changes. Traditionally, information on urban forest structure has been gathered on street and park trees (McBride and Nowak 1989; Hauer et al. 1994; Welch 1994), but as management objectives change to include environmental services, inventories have been expanded to encompass vegetation in other parts of the urban for- est. These include residential, industrial, and abandoned lands (McPherson et al. 1997). Besides being implemented to pro- vide structural information (e.g., tree species, number, size and/ or age, location) (Nowak and Crane 1998; Nowak et al. 2008a; Nowak et al. 2008b), inventories are also the basis for deriving measurements of ecosystem services, including carbon storage, carbon sequestration, and energy savings (Nowak et al. 2008a). Several methods have been used to conduct urban tree inven- tories, including sampling (Nowak and Crane 1998; Nowak et al. 2008a; Nowak et al. 2008b) and 100% inventories (Martin 2011). Sampling is conducted by collecting data on a predeter- mined number of trees or plots within a given area to provide an estimate of a larger area (McBride and Nowak 1989; Jaenson et al. 1992; Nowak et al. 2008a; Nowak et al. 2008b). Using 100% inventories every tree is located and data are recorded, provid- ing the most accurate information (Jaenson et al. 1992; Nowak et al. 2008a). However, unless this inventory is being conducted ©2013 International Society of Arboriculture on a relatively small area, it may not be as efficient as sampling (Jaenson et al. 1992; Nowak et al., 2008a; Nowak et al. 2008b). Personnel demands, resources, and time need to be taken into consideration. Jaenson et al. (1992) noted that a full inventory conducted in Ithaca, New York, U.S., required a period of five months with a total of six people to finish the 5,600 tree inven- tory (Bassuk and Jaenson 1988). Jaenson et al. (1992) also noted that a partial inventory could be conducted at a more affordable rate and would only take days instead of months. However, while sampling may be more cost effective and require fewer person- nel for a shorter period of time, the protocol (number of plots, size of plots, stratification method, etc.) followed can have an impact on both time and cost effectiveness. Nowak et al. (2008b) conducted research on this subject and noted that the number and size of sample plots are the major factors that urban forest man- agers need to consider when evaluating the protocols to follow and their effects on the overall costs. Time for data analysis and updating must also be taken into account (Jaenson et al. 1992) when comparing complete with sample inventories. Finally, the amount of time required for checking data integrity will also be affected by the size of the inventory as larger inventories will require more personnel and may even require the help of less quali- fied individuals (volunteers for example) to aid in data collection. The United States Department of Agriculture Forest Service (USDA FS) developed a protocol in the 1990s, originally named the Urban Forest Effects (UFORE) model and now referred to as i-Tree Eco (i-Tree 2010a), to be used in conducting tree inventories in urban settings and to provide information on eco- system services (Nowak and Crane 1998; Nowak et al. 2008a).
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