-For tree inventories especially, specialized computer software is recommended.
Comprehensive tree inventory systems, as discussed below, can provide a wealth of information about the urban forest and municipal tree care operations. However, additional records are normally required to cover aspects of the tree management program such as long-term planning, public education, ordinance enforcement, and program administration. For example, tabulations of tree-related permits, ordinance violations, and enforcement actions may be needed to assess the implementation of certain tree ordinance provisions.
Trees have fixed locations and exert many of their effects, such as shading, on a specific geographic area. Tree growth is also influenced by local site conditions. If tree resource data are linked to the geographic coordinates of the tree or stand of trees they describe, tree information can be displayed and analyzed spatially. Geographic information system (GIS) software is therefore a logical choice for storing and manipulating tree resource data.
Geographic information systems are computer systems capable of assembling, storing, manipulating, and displaying data that are identified according to their locations. Such data may be referred to as geographically referenced information or geospatial data. A GIS can be thought of as an electronic map that includes data associated with specific points, lines, polygons, and/or pixels that represent fixed geographic locations. Numerous websites describe GIS and its capabilities. A few general sites include:
GIS software is available for most common computer operating systems and hardware platforms. Several websites that list commercially available GIS software vendors are listed below:
Many commercial GIS vendors distribute free demonstration versions of their software for evaluation. Some public domain GIS software is also available for free download. GRASS GIS (Geographic Resources Analysis Support System), a multiplatform, open source GIS, can be downloaded from Baylor University and various mirror sites (see http://www.baylor.edu/grass/).
Base data layers for GIS systems are available for download from a number of federal and state sources. For example, the US Census Bureau Geography page http://www.census.gov/geo/www/ provides geographic data related to the census, including spatial data for geographic features such as roads, railroads, rivers, and lakes, as well as legal and statistical geographic areas.
Evaluation example: Creating a forest/tree GIS
To show how Dane County's (Wisconsin) forests and individual trees could be mapped and inventoried using a geographic information system (GIS), the Land Information and Computer Graphics Facility, University of Wisconsin-Madison conducted a pilot project for the Dane County Tree Board. The report at http://www.forests.org/danetree/forestgis.htm provides the results and lessons of this project.
Tree inventory software is commonly used to store information about intensively-managed trees, especially those along streets and in parks. In most communities, only trees managed by the city or county are included in tree inventories. These may include both trees on public land and on private property along the public rights-of-way (ROW). The most basic tree inventories are simply lists of the locations and descriptions of individual trees. More advanced inventories include information on site characteristics, past maintenance, and anticipated maintenance needs for each tree. Complete inventories provide a direct means for assessing the relationship between trees, planting locations, and maintenance expenditures. The types of information included in the inventory should reflect the goals of the ordinance and the overall tree management strategy. Some of the variables which may be evaluated are as follows:
Trees: species, diameter, height, canopy spread, age or age estimate, remaining life expectancy, condition with respect to health and structural integrity (hazard), value, historical significance;
Sites: location coded by street address, distance along street, or actual coordinates (e.g., latitude and longitude), planting site specifications (e.g., 3 ft tree well, 4 ft parkway, in lawn 7 ft from sidewalk), proximity to above- or below-ground utilities, potential for replanting if empty, soil type, known soil limitations (e.g., persistent soil-borne diseases such as Armillaria, high salt or boron levels, excessive compaction, low water-holding capacity, poor drainage);
Cultural practices: past cultural inputs by date of action including planting, fertilization, pruning, cabling, pest control, removal; presence of maintenance problems by date observed, including sidewalk damage, limb breakage, severe disease or insect attack; resident inquiries or complaints; projected maintenance needs and priority;
Costs: materials costs, equipment use, and personnel hours incurred for each cultural operation by date.
Data for tree inventories may be compiled from one or more sources. Ground survey techniques are typically used to compile most of the basic tree and site attributes. Site information may be available from an existing municipal GIS or plans. Job records are the source of most data related to cultural practices and their associated costs. Most tree inventory software is designed to allow for direct entry of work records, tree data, and site information into the program and provide a central database that permits the tree program manager to view all of the pertinent information about a tree when scheduling maintenance. Various vendors produce tree inventory software, including software that are extensions of popular GIS programs such as ArcView®. Using commercial software can reduce the amount of time required to develop custom programs or GIS applications, but may not provide the same degree of flexibility and integration with existing software that might be obtained by having custom software developed in-house or through a contractor.
Olig, G. A.; Miller, R. W. 1997 A Guide to Street Tree Inventory Software. Online at http://www.na.fs.fed.us/spfo/pubs/uf/streettree/toc.htm. This review is several years old. Many of the programs reviewed are still available, although vendors should be contacted for information on their most current releases.
The Community Forestry Education Project (Rochester, NY) provides free spreadsheet (MS Excel) and database (MS Access) street tree inventory templates. These templates are not GIS-based, but by adding geographic coordinates for each tree to the template, a GIS-ready database could be constructed.
Evaluation example: Street tree inventory as part of a citywide GIS
An example of a street tree inventory that is integrated with a municipal GIS can be accessed interactively online at the City of Ithaca (NY) GIS website. The City of Ithaca started developing its GIS mapping effort in 1990 using base map information derived from photogrammetrically produced maps. Many of the GIS layers are available to the public via a standard web browser. In addition to street trees, the GIS layers available on the Internet server include buildings, property lines, utilities, sidewalks, and boundaries of districts and other areas. The Internet interface (which uses MapInfo's MapXSite software) allows users to zoom and pan on a map or to locate sites by address or tax parcel number. To view street trees in the GIS, check to see that the "Trees" layer is turned on and zoom in 0.25 miles or less. If you set the "click on the map" option to "get info", you can view data for any individual tree by clicking on it and then clicking on the tree common name. Only a portion of the data stored in the GIS is made available to public users; city staff and other authorized users have access to additional information and data query functions.
Although GIS greatly enhances the options for manipulating and presenting spatial data, simpler databases can also provide the information needed for urban forest analyses. The City of Cypress, California, provides a classic example of how tree records can be used to evaluate and adjust tree management practices. The city implemented a computerized tree inventory system in 1971 that included detailed work records for each tree. In 1981, they compiled data from the inventory database to determine which trees and planting situations were causing the most damage to concrete curbs and sidewalks. This information was used to adjust the tree management program in several ways. Improved tree selection guidelines were developed to obtain better compatibility between the trees and planting sites. The data were also used to predict locations where future damage was most likely to occur. These areas were targeted for a phased removal program, in order to head off future problems without an abrupt removal of the entire street tree canopy. Finally, a tree ordinance was adopted that provided the authorization needed for the city to control street tree planting, maintenance, and removal.
As we have noted elsewhere, most trees within communities are on private properties outside of the public ROW, so inventories of publicly-managed trees include only a small portion of the community forest. Although trees on private properties are not commonly included in city tree inventories, many cities already collect data on certain classes of trees in connection with planning and permitting processes. Virtually all site development plans include a landscape plan that includes both existing trees that are retained on site as well as new trees that are planted as a condition of plan approval. Tree attributes such as species and size are commonly available from these plans, and more detailed information may be available if a tree survey is required in the development process. If these data were compiled in a master inventory, preferably GIS-based, it would provide a powerful tool for monitoring ordinance compliance and efficacy. Historic or heritage trees could also be included in such an inventory if the protection of such trees is a local priority.
Compilation of this tree information into a GIS may require an additional step beyond current practices. However, if the city or county requires applicants to provide geospatial coordinates and attributes for trees shown on plans, adding this data to an existing GIS would require relatively little additional effort. A consolidated inventory of these trees would allow the local government to track the fate of trees that have been planted or conserved as a result of local ordinances or regulations. An inventory of regulated trees could be used to more easily determine:
Many, if not most, communities require tree planting or retention as a condition of approving various projects. However, if the long-term results of these regulatory practices cannot be assessed readily, it will be difficult to determine whether the regulations are really accomplishing their goals. By consolidating and organizing data on regulated trees that is already being collected, local governments would be able to assess the impacts of their tree regulations more easily, and could use this information to improve enforcement and/or develop better regulations.
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