What is the current state of your community forest?
Do you know…?
- The number, species and age composition, and health of trees growing on public street rights-of-way and other public properties.
- The percent of the community covered by tree canopy.
- The rate of land development over the last 5 to 10 years (number of acres developed, by zoning district, by year).
- The number of parcels and acres within each zoning district (with the number of parcels and acres developed and remaining vacant).
- The budget for community forestry activities, including the funding available for professional expertise in administering the tree ordinance.
This is important information that can help to guide the development of your tree ordinance. Tree inventories and tree canopy cover studies can help to determine where trees are located, and their composition and health.
Working with the planning department, the arborist can research how many development permits have been issued over last several years for various types of developments. The GIS administrator should be able to provide information on the number of acres within each zoning district, and may also be able to provide information on how many parcels and acres are currently developed (and undeveloped), within each district.
MEASURING TREE CANOPY COVER
There are several methods that are used to measure tree canopy cover that vary widely in their complexity and expense.
DOT GRID METHOD. A simple, although time consuming, method of estimating the amount of tree canopy cover in a community is one in which aerial photographs are covered with a transparent dot grid, and every dot that falls on top of tree canopy is counted. The total number of dots that fall on tree canopies is divided by the total number of dots in the grid to get the percent tree canopy cover.
This project can be done by the arborist, or by trained volunteers and government staff. In fact, one of the greatest advantages of using this method is to educate staff, tree board members, and other interested persons about where tree canopy cover exists, and where it does not.
This method has been used to estimate tree canopy cover–as well as impervious surfaces, open soil, water, and other vegetation–in Cartersville, Covington, Dalton, Jefferson, Oxford, and Smyrna, to name a few.
In Smyrna, high school students studying the environment completed the analysis for the Smyrna Tree Board. Assisting were a consulting arborist, tree board members, and the student’s environmental education instructor. Click here to see a report of the results of Smyrna’s tree canopy cover measurement project.
Additional documentation used for this project is available by clicking below:
- Volunteer Sign-in Sheet
- Criteria and Procedures for Measuring Tree Canopy Cover
- Instructions for the City of Smyrna Tree Canopy Study
- Tree Canopy Tally Sheet
- Supply List for Tree Canopy Study
I-TREE CANOPY. i-Tree Canopy is part of a software suite, i-Tree Tools, for community tree assessment developed by the Davey Tree Expert Company and the USDA Forest Service. It is available for free to anyone wishing to measure the tree canopy and other land cover in a neighborhood, city, county, or region.
i-Tree Canopy uses current aerial imagery that can be uploaded from their site. Users determine the sampling intensity they desire and define the land cover types they wish to measure. The program covers the study area with an appropriate number of measurement sites (dots, as in our dot grid method) for the desired sampling intensity. The user places each dot in one of the defined categories, and after all dots are categorized, the program prints a set of reports and statistics, including the tree canopy cover percent and tree benefits.
Winterville has recently measured their tree canopy cover using i-Tree Canopy and found that their current tree canopy is 58 percent. This measurement was made prior to the community beginning the process of developing their first tree ordinance.
Milton also used i-Tree Canopy to measure their current tree canopy cover as they began the revision of their existing tree ordinance. Using this program, the city estimates that Milton’s current tree canopy cover is approximately 58 percent. A copy of the i-Tree Canopy cover assessment and tree benefits report for Milton is available here.
For more information on i-Tree Canopy and other tree assessment tools, visit www.itreetools.org.
INFRARED SATELLITE IMAGERY
Measuring tree cover using infrared satellite imagery is the most technically advanced method of determining tree cover on a citywide, countywide, or regional scale and usually the most expensive. These analyses can be provided by environmental engineering companies.
Urban Forestry South, the technology and information source site of the U.S. Forest Service Southern Region, has collected information on tree canopy studies from across the U.S. Enter “tree canopy study” in the search box to get a current list of studies of interest.
Talk with other communities in your region to see if they have done this type of analysis. They should be able to provide you with the specifications they used to solicit bids for such an analysis, the cost, the results, and how they’ve used these results in writing or revising their tree ordinance and tree management program.
A 2008 article in the Journal of Arboriculture & Urban Forestry, titled Assessing Urban Forest Canopy Cover Using Airborne or Satellite Imagery by Jeffrey T. Walton, David J. Nowak, and Eric J. Greenfield, provides further information about the use of aerial imagery to assess urban forest canopy cover.