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The BLT Ordinance

Buck Abbey, ASLA, Robert Reich School of Landscape Architecture, Louisiana State University






The BLT now requires a tree density standard and tree canopy calculations for each development project. There is also a tree banking option that allows more credit for preserving existing trees.


"Cities around the world are making major investments to infrastructure, creating jobs and improving their quality of life."--Mayor Michael Bloomberg, Mayor of New York City. 2008

Sustainable Urban Forests

We have written about the Planyc sustainability program launched by NYC Mayor Bloomberg in 2007. New Yorkers understand the future of their city is based on making the city sustainable, while meeting the challenges posed by an environment under stress from growth and development.

But other cities, smaller cities across the country, are doing some of the same kind of thinking. They are passing green laws that will preserve, protect and rebuild their urban forests, public open spaces and community parks. One such urbanizing area is Gwinnett County, Georgia, located in suburban Atlanta.






Lawrenceville, Georgia in suburban Atlanta is the county seat of Gwinnett County. The canopy coverage standard in Gwinnett is set at 16 TDU (tree density units/acre).


The BLT Ordinance

The Gwinnett County tree ordinance, referred to locally as the BLT Ordinance (buffer, landscape & tree ordinance) is one of the best examples of a green law moving toward that class of green laws referred to as "super tree laws." This special class of green law is based upon sustainable practices, combine both tree management with landscape requirements and facilitate tree preservation. (Gwinnett County Municipal Code, Chapter 118, Vegetation, Sec. 118.1, 1987, amended 2001, 2003, 2007.)

This ordinance has been modified several times since its enactment in 1987. In each instance it has become more tailored to sustainability. The most recent amendment, December 2007, enhances tree preservation standards for residential and commercial property as well as street tree plantings areas on public property fronting private development. The BLT now requires a tree density standard and tree canopy calculations for each development project. In addition, the revision now provides a tree banking option and allows more credit for preserving existing trees.






Gwinnett County's "BLT ordinance" (buffer, landscape and tree) is a special class of green law based on sustainable practices, combining tree management with landscape requirements. A tree ordinance or landscape code is only as effective as its enforcement. The BLT is administered by the director of planning and development though agents who work directly with the public and developers.


The Technical Standards

The purpose of BLT is to preserve and enhance the county’s natural environment and to protect its urban forest canopy to the extent that all development meets a uniform standard of canopy coverage, landscaping and buffering of conflicting land uses.

Technical standards include the design of street yards, buffers, screens, and parking lot plantings, all of which are major components of Gwinnett public policy. In addition, the BLT calls for water efficient landscape design and the use of native plant material species.

The foundation of the ordinance is built around three main purposes. They include the directives to "preserve and enhance the county’s natural environment; the preservation, protection and planting of trees; and the provision of natural and/or planted buffers" between dissimilar land uses and zoning districts. These are all sustainable practices.

The code defines several new urban forestry concepts not seen in most community tree laws. The program quantifiably rests on tree calculations where diameter in inches is converted to tree density units (TDU).






In Dec. 2007, Gwinnett County amended it BLT ordinance to enhance tree preservation standards for residential and commercial property and street tree planting areas on public property fronting private development.


Canopy Preservation Standard

In this community the urban forest is to be sustained by ensuring a benchmark for urban forest canopy coverage within the county. The canopy coverage standard in Gwinnett is set at 16 TDU (tree density units/acre). The calculations for this are simple. First the area of the site is determined. All required buffer areas, servitudes and detention ponds over one-acre are subtracted to determine total area of development site. This number in acres is multiplied by 16 to determine required TDU required on the site.

The site is surveyed to determine the total number of DBA caliper inches of trees to be preserved. Appendix B & C from the BLT are used to determine the total TDU that will be subtracted from the required TDUs. Appendix B & C provide a TDU factor for all tree diameters from three inches to 50 inches, DBH for preserved trees from one inch to 14 inches for replacement trees.

Administrating the Code

But as written before in this column, the most important thing about any green law is the method and tools by which it is administered. A tree ordinance or landscape code with no enforcement procedure will not be effective.

The BLT is administered by the director of planning and development though agents who work directly with the general public and development community. According to Article 8 of this code, three common administrative methods are used to administer the BLT. They include inspections, plan review and the issuance or revocation of permits. The landscape code applies to one or more permits that are required to develop property. They include development permits, grading permits, clearing & grubbing permits, building permits and occupancy permits.

Landscape, tree preservation and replacement plans are submitted for review and approval prior to receiving a development or clearing permit. Trees cannot be removed without the landscape plan and clearing permit. A citation, summons, or accusation can be issued by the inspector on a standard ticket form. Violation may result in a fine of $100 to $1,000 a day as well as 60 days in jail upon conviction in court.

The BLT ordinance is worthy of being considered as a model that could be used to lead other communities toward a sustainable urban forest. There is a lot to learn by reading the Gwinnett BLT ordinance and its companion documents BLT Ordinance Handbook and Gwinnett Development Regulations. All are available at www.gwinnettcounty.com






D.G. "Buck" Abbey, Associate Professor of Landscape Architecture at Louisiana State University, is LASN's Associate Editor for Ordinances.




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November 22, 2019, 12:56 pm PDT

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