They also might contain design standards for street walls, habitat preservation areas and in rarer instances minimum canopy requirements. It is the later that is catching a lot of attention these days by those that write community-planning regulations as community after community struggle with ways to preserve the native urban forest canopy. It is important for a community to set tree canopy goals within their codes and regulations because most communities have lost tree cover over the last 30 years due to new urban development.

Forsyth County, Georgia uses a tree density standard (TDS) based upon caliper inches of the diameter of trees, as well as a site density factor (SDF). SDF is simply the number of trees per acre.

Tree Preservation

There are several good examples or cutting edge tree ordinances in the Georgia, South Carolina, North Carolina, Virginia and Maryland. All of these states show leadership in urban forestry and in the development of municipal policy toward trees. The preservation of urban forest canopy is of special interest in this region.

Counties surrounding Atlanta, Georgia, including Fulton, Dekalb, Gwinnett, Fayette, Forsyth, Henry, Clayton, Rockdale and Cobb, all have tree ordinances and landscape codes geared toward preserving trees. Some of the most innovative tree ordinances in the country are being written in this area.

One of the ideas contained in all of these outstanding tree preservation regulations is there ought to be a minimum tree canopy for every development site. Further, this canopy must be preserved or replanted to eventually grow into the minimum canopy requirement. American Forests recommends cities have at minimum a canopy coverage between 25 and 40 percent. For suburban residential zoning districts, 35 to 50 percent; for urban multifamily residential zoning districts, 18 to 25 percent; and within central business zoning districts, nine to 15 percent coverage. The first number represents values in the arid west and the latter the wetter east.

Baton Rouge, Louisiana, for instance, has a minimum tree canopy requirement of 17 trees per acre. Louisiana State University is pictured.

Minimum Canopy Standards

Perhaps the most important concern of a landscape code is to set minimum canopy standards. These standards can be set for the city as a whole, by zoned land use district, or by each developed building lot. The minimum canopy standard can be measured in one of four ways: canopy coverage area, percentage of site ground space devoted to trees, numbers of tree per development site, or number of caliper inches per acre.

Forsyth County, Georgia uses a tree density standard (TDS) based upon caliper inches of the diameter of a tree, as well as a site density factor (SDF). SDF is simply the number of trees per acre. Baton Rouge, Louisiana, for instance, has a standard of 17 trees per acre; Charleston, South Carolina sets a minimum standard of 160 DBH caliper inches per acre. DBH is the outside bark diameter at breast height.

Fulton County, Georgia calculates tree density for replacement purposes within commercial districts with the use of calculating tables and a simple formula for 15, 20, or 30 trees per acre, aka DFS?EUR??,,????'?????<

Another way to think about this is how many trees per acre are required in Fulton County on a per acre basis if the development is occurring on land with no existing canopy coverage. The trees must meet the DFS. Working the table backward and using five-inch DBH trees in the design the answer is quickly found: 33 five-inch DBH trees per acre. Or, if one chooses to meet the DFS with two-inch DBH trees, then 60 two-inch DBH trees would be planted.

Having canopy standards as part of the landscape ordinance allow a community to have a quantifiable mitigation program to ensure that when existing trees are removed, they get replanted somewhere in the city. Communities can thus maintain a stable urban forest that meets the needs of everyone for clean air, pure water and meet the ?EUR??,,????'?????<

Each community should inventory their tree stock periodically to measure canopy coverage and ascertain the composition, health, texture (deciduous vs. evergreen, size, height, and age and caliper inches per acre) and economic value.

Minimum canopy standards should be set locally based upon each community?EUR??,,????'?????<

Landscape codes all require the planting of trees. Unfortunately, these trees are planted without having a minimum tree canopy standard. Landscape codes could provide such a standard and then measure it against the landscape plan submitted for approval. This will allow city landscape administrators to know which trees are being preserved and how trees are being planted to comprise the future urban forest canopy.

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