Monday, August 23, 2010
Thougts about our Tree Canopy Plan
Our Environmental Advisory Board has been tasked with looking at our Tree Canopy within the City and develop some preliminary information to help create our canopy plan. We lost 50% of our tree canopy after Hurricane Ivan and this directly affects the quality of our ozone. Here are some thoughts from WFRPC
Establish Tree Canopy Targets
To maximize the benefits provided by urban forests and to track its condition in a specific location, the first step is to establish a goal for tree canopy cover. Tree canopy cover (the percent of a city’s land area shaded by trees) targets provide a useful way to assess how close a city’s green infrastructure comes to its potential. Such targets take into account factors such as local climate and other natural ecological conditions. While the ideal tree canopy for Philadelphia, for example, is very different than Phoenix, each has a tree cover target or goal that is ideal for them. To help guide city leaders in setting tree cover targets for their communities, American Forests produced the following generic guidelines for specific zoning categories for cities in the United States east of the Mississippi and in the Pacific Northwest:
• Metropolitan area—average tree cover counting all zones = 40 percent;
• Suburban Residential zones = 50 percent;
• Urban Residential = 25 percent;
• Central Business District = 15 percent.
Cities are starting to incorporate these guidelines into public policy. For example, less than a year after their urban ecosystem analysis revealed that the Roanoke, Va., area had only a 32 percent tree canopy; the city council passed an Urban Forestry Plan. The top priorities include reaching a 40 percent citywide tree canopy goal within ten years and requirements for more tree planting and tree protection during new land development. The city has also updated their zoning ordinance that specifies tree canopy cover by land use and specifies minimum tree canopy cover in parking lots.
While these percentages are a good starting point for communities, they should be used only as a guide. Geography and local climate are important factors in establishing more precise local targets. The average urban tree cover for 20 states in the northeastern quarter of the country is 30 percent.
American Forests analyzed tree cover in about a dozen metro areas nationwide and found them to be 25 to 35 percent depending on their underlying environmental conditions. As you might expect, cities in the Southwest United States have less tree cover than cities in the Mid-Atlantic States. From the analysis, American Forests was able to identify potential, if somewhat generalized, tree cover targets. As previously stated, these recommendations find that average tree cover in metro areas east of the Mississippi and in the Pacific Northwest should be about 40 percent, while cities in the dry Southwest and Plains states with much smaller natural tree covers should shoot for tree targets of about 30 percent.
A decision to maintain a specific percentage of the green infrastructure must be made at the highest levels of government so that the managing departments can carry out the detailed actions needed to meet those goals. The tree cover targets and the challenge to incorporate trees into all growth and development activities must be shared by key departments of city and county governments as well as by the private building industry.
Allowing construction practices that damage, kill, or remove trees—whether they occur on public or private property—without replacing them should no longer be acceptable. Assuring trees will live is not a small challenge, but one that must be accepted by everyone that builds infrastructure.