GIS branches into urban forest management
Cleveland Heights, Ohio, City Forester Thomas Morgan has access to all the usual tools associated with his profession. Like anyone charged with the maintenance of large stands of trees, he’s got pruning shears, chain saws, mowers, sprinkler systems and fertilizer spreaders. But Morgan has a leg up on most other urban foresters because he’s also got a geographic information system (GIS).
A GIS integrates data and presents it in a graphic format, allowing urban foresters to plot tree location and related information on computerized maps. Graphic symbols representing trees are displayed on the maps and are linked to a database containing tree characteristic information for each tree in the inventory.
In communities that already have GIS, other departments can furnish maps and database information to forestry departments to be used in development, planning or other city tree-related activities. Urban foresters can use GIS to analyze trees and their proximity to roads, sidewalks and utility lines, for example.
In addition to showing the number of trees in a given area, maps can show the distribution of trees threatened by disease or the locations of certain tree species or trees to be removed so that contractors can get to construction sites.
A decade ago, Morgan was itching for a GIS to help manage his urban forest program. Recognizing the importance of GIS in today’s government environment, Morgan was determined to be on the cutting edge of the technology.
Then, in 1993, the Ohio Department of Natural Resources awarded Morgan’s department an Urban Forestry Management grant. Still, the forestry department budget would not support development of a GIS on its own, so Morgan immediately set to work encouraging other city departments to collaborate on a GIs.
As a result, the water and management information systems departments are working with the forestry department to implement GIS on a citywide basis. Cleveland Heights’ MIS department makes sure that GIS data created by the forestry department will be compatible with other city departments that will someday use the system.
For Morgan, the system has made his job easier. Additionally, grant money has enabled him to purchase tree inventory management software and a hand-held computer to collect tree inventory information, including tree location, species, diameter, condition, maintenance needs, hardscape (sidewalks, curbs, etc.) damage and potential planting sites. Once information is collected for each tree, it is entered into a computer database linked to map symbols representing tree sites.
A PLANNING ADVANTAGE
GIS gives urban foresters a planning advantage by allowing them to anticipate uses of treed areas. And it can produce maps of city facilities, parking lots and parks with a higher level of accuracy than the department’s street tree maps which use address matching to locate trees.
The trees in Cleveland Heights’ six parks, seven large facilities and 30 parking lots will eventually be included in the computer program. “With GIS we will know exactly where our trees are,” Morgan says. “By having a detailed inventory, we can manage our forest so it grows into the 21st century.”
Morgan’s short-term goal for the GIS is to use it for planning, planting and object removal; the long-term goal is to have the citywide GIS linked with the water and sewer departments. “This link will help us immeasurably with our planting plans,” Morgan says. “We want as much information as possible in map layers so we can coordinate projects with other departments.”
In preparation for the GIS, various Cleveland Heights departments had aerial pictures taken of the city. Engineers will use the photos to produce a topographic map and create a detailed digital map of the entire city, including layers for trees, streets, sidewalks, sewers and buildings.
Accurate street maps are essential for the development of a GIS. TIGER (Topographically Integrated Geographic Encoding and Referencing) file maps, available from the Census Bureau, contain information based on the 1990 census and are relatively inexpensive (about $300) for an entire county or state. However, converting and correcting these maps can be time consuming.
Cleveland Heights used a TIGER map file for plotting its street tree locations. Using this method allowed the department to match 95 percent of the tree locations before any data correction was done to the maps. As the project proceeds, street maps will be corrected so that the remaining tree addresses match properly.
Maps prepared by distributors who specialize in converting TIGER file maps for specific GIS systems can be obtained for about $400 to $500. Although these maps are more expensive, they save the time and money in future map correction.
LEVELS OF GIS USE
Once Morgan has created the tree inventory for Cleveland Heights, the GIS program can be installed, and tree locations can be plotted on a computerized map of the community through address matching or manual plotting. Integrating GIS technology with an urban forest management program can be accomplished with varying degrees of cost, accuracy, time and resources. Depending on a community’s needs and financial resources, there are three levels of GIS implementation from which to choose: visualization, planning and detailed planning/spatial analysis.
Visualization. Visualization is the least expensive GIS option and the easiest to implement. A picture of the urban forest allows immediate recognition of geographic relationships and potentially hazardous situations. For example, maps can be produced that show where tree work should be performed or where certain tree species have been overplanted.
Visualization can be achieved with limited spatial accuracy, minimal cost and time. With urban forestry it is possible to see the relationship of plant characteristics to other environmental attributes and structures in the community.
Additionally, visualization gives a rough estimate of tree locations using address matching to plot trees based on address ranges for each segment on a street map. One limitation is that only one tree symbol is used to represent all of the trees at each address. However, users can simply select the symbol to view all of the tree information for that address.
Planning. GIS not only helps with visualization but it is also a useful planning tool, allowing for identification of current problems and potential dilemmas. Tree inventory specialists use a hard copy tree inventory map to manually plot point locations for trees which are then plotted in the GIS application.
At this level, tree locations can be mapped more accurately in relation to each other and city streets. Each tree is represented by a symbol on a GIS map layer, and, although distances are not exact, maps show trees in relation to each other, buildings, streets and other objects.
Should a building be tom down or a street widened, maps will show more precisely which trees will be affected. When planning a park, bed boundaries and planting sites that are accurate within several feet can be set.
Detailed Planning/Spatial Analysis. GIS can also aid urban foresters with spatial analysis. Because maps are so precise when accurate mapping is done, the distance of objects from trees can be shown within several feet or even inches. Using spatial analysis, users can display every tree within 20 feet of an intersection to see where street sign conflicts are probable. A more sophisticated spatial analysis can show all trees of a species within a certain distance of a diseased tree of the same species.
This is the most accurate GIS level and offers an increased degree of reliability with tree locations plotted manually on a very accurate street map. If information on a pest problem such as Dutch Elm disease is collected, the location of each affected tree can be displayed, and the GIS program can create buffer zones around infested trees and indicate healthy trees that may be at risk.
This level also is the most accurate at executing spatial queries. For example, a query can be executed that will identify every tree within 20 feet of an intersection so that city workers can use maps to check if any trees are blocking stop signs. Potential or actual conflicts with utilities, hardscape and other elements of the city infrastructure can also be identified.
No matter what GIS level a community chooses, thorough investigation should be conducted before a selection is made. Training is also important since poorly trained users can make costly errors.
Laura Miller is a communications specialist with the Davey Resource Group, a division of The Davey Tree Expert Co., Kent, Ohio.