392 occasionally collected include tree damage, tree spacing, grow- ing and plantable space, and visual diagrams of the site. In general, the data variables can be summarized into five categories: 1) location, 2) tree species and dimension, 3) tree condition, 4) site characteristics and conditions, and 5) associ- ated cover type information (e.g., ground cover, shrubs, build- ings). Of these categories, location, tree species and dimensions, and tree condition are commonly collected in assessing urban forest structure. Location information is required to relocate the trees and as a record of the data collection procedure. Tree species, dimensions, and condition are basic attributes to quan- tify the urban forest structure; these are variables that can be directly recorded for a tree. Aggregation of individual tree in- formation allows for quantification of urban forest population attributes (e.g., total number of trees, species composition). This basic individual tree information is also important in quantifying ecosystem services and values, and is essential to develop appro- priate management plans to sustain urban forest cover and health. Site characteristics and conditions often are collected for street trees to assess current and potential planting sites to aid in tree management. Associated cover type information can be collected to help assess other cover types that are part of the urban eco- system and to help quantify the interactions among cover types to aid in management or the quantification of ecosystem services (e.g., energy conservation). All of these variables aid in under- standing urban forest structure and can aid in urban forest man- agement. The decision on what variables are actually collected depends upon the local objectives of the data collection. INTERNATIONAL STANDARDIZATION OF URBAN FOREST DATA COLLECTION Standardizing field data collection could provide significant gains in facilitating data collection and analyzing information for urban forest management. Exclusive of inventories, many stud- ies use some sort of random plot design to collect field data on the urban forest. These studies often collect core variables re- lated to location, species, tree dimensions, and tree condition. Development of international standards related to urban forest sampling and core variables (e.g., standard species codes) could greatly assist urban forestry globally. By adhering to standard methods of urban forest data collection, various programs can be developed and shared internationally to aid in data collection, analysis, reporting, and management. The i-Tree software (www.itreetools.org) is a suite of pro- grams that is currently attempting to standardize data collection and analysis of urban forest samples and inventories. Core vari- ables would be required, but standardized supplemental variables could also be added to aid in analysis or management depending on the user’s desires. For example, detailed standardized tree damage variables or site characteristic variables could be devel- oped as supplemental variables for analysis. Standardized analy- sis and reporting of data could also be developed. Groups interested in the international aspects of urban for- estry, such as the International Society of Arboriculture (ISA) and the International Union of Forestry Research Organizations (IUFRO), could work toward developing international standards for urban forest data collection and analysis. These new stan- dards could relate to plot design and distribution (e.g., random versus stratified random sampling, plot sizes), analysis and re- porting methods, and core data standards. These standards should link with existing forest measurement standards (e.g., ©2008 International Society of Arboriculture Nowak: Summary and Conclusions U.S. Forest Service Forest Inventory and Analysis standards) (Cumming et al. 2008) to help ensure integration with other forest programs. To facilitate the development of standards, the ISA, IUFRO, and scientists from the Research and Development branch of the U.S. Forest Service will be approaching the Soci- ety of Municipal Arborists, the European Arboricultural Council, and other international organizations within the urban forestry network to stimulate interest in and establishment of interna- tional urban forest data standards. Once standards are established, new programs and tools could be developed to help urban foresters across the world in collect- ing, analyzing, and reporting on their urban forests. The use of standards would be optional, but entities that choose to use the standards and associated tools would be afforded a relatively low-cost means to quantify and monitor their resource and com- pare data among other urban areas throughout the world. The use of urban forest data and analysis standards could also be used to help develop minimum standards or goals for urban forest struc- ture (e.g., tree cover, tree density, species diversity) and a means to monitor attainment of these standards. Given current technology, international standards could be disseminated to help move urban forest management to a fore- front in many local to international arenas. These new standards could advance integration of urban forestry within regional, na- tional, and international programs (e.g., climate change pro- grams), aid in long-term monitoring of urban forests, facilitate urban forest management to improve urban forest cover and health, and consequently enhance environmental quality and hu- man health in urban areas. LITERATURE CITED Cumming, A.B., D.B. Twardus, and D.J. Nowak. 2008. Urban forest health monitoring: Large scale assessments in the United States. Ar- boriculture and Urban Forestry 34:341–346. Jim, C.Y. 2008. Multi-purpose census methodology to assess urban forest structure in Hong Kong. Arboriculture and Urban Forestry 34:366–378. McBride, J.R. 2008. A method for characterizing urban forest compo- sition and structure for landscape architects and urban planners. Ar- boriculture and Urban Forestry 34:359–365. Ning, Z.H., X.Y. He, C.F. Liu, and K.K. Abdollahi. 2008. Assessing urban forest structure and health in Shenyang, China. Arboriculture and Urban Forestry 34:379–385. Nowak, D.J., D.E. Crane, J.C. Stevens, R.E. Hoehn, J.T. Walton, and J. Bond. 2008a. A ground-based method of assessing urban forest struc- ture and ecosystem services. Arboriculture and Urban Forestry 34: 347–358. Nowak, D.J., J.T. Walton, J.C. Stevens, D.E. Crane, and R.E. Hoehn. 2008b. Effect of plot and sample size on timing and precision of urban forest assessments. Arboriculture and Urban Forestry 34: 386–390. Walton, J.T., D.J. Nowak, and E.J. Greenfield. 2008. Assessing urban forest canopy cover using airborne or satellite imagery. Arboriculture and Urban Forestry 34:334–340. David J. Nowak Northern Research Station USDA Forest Service SUNY-ESF 5 Moon Library 1 Forestry Drive Syracuse, NY 13210, U.S.
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