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Understanding Tree Ordinances

Tree ordinances have been around for a long time. Some are from as far back as early colonial times when clearing of all of your land for farming was prohibited (seems that the loss of future firewood was an issue). Over the years, tree regulation has taken on many different forms: from the need for street heat abatement (early Philadelphia required every main street house to have a tree in front to provide street shade) to the current design standards suggesting various percentages of tree canopy be maintained across a community.  Some ordinances apply only to trees on public property, while others regulate all publicly owned and privately owned trees within a city.

Tree ordinances are regulations that control how trees are maintained, conserved or removed. This inter-ference with property rights rests on the idea that trees have both benefits and risks that impact everyone in the community. While some communities do not regulate trees in a homeowner’s front yard, they will vigorously regulate trees in a neighborhood grocery store’s parking lot, even though both are growing on private property.

Some tree ordinances are part of a community’s “unified development code” and others are stand-alone ordinances that regulate trees. Some have provisions that apply only to downtown business districts, others apply only to developments larger than 5 acres, while some apply only to trees over a certain size or age or historic value.

It is important to keep in mind that tree ordinances are, or rather should be, “living documents”, that is, they change and grow as communities change and grow in size or values.  Many communities find that trees and tree ordinances are good for business and improve the economic vitality of underused and/or underserved areas. This in turn improves the tax base and community revenue, as well as making streets more attractive and welcoming.

Often times tree ordinances start out as simple one or two page documents that seek to protect trees on public properties, parks and government buildings so that cities might qualify for the National Arbor Day Foundation’s “Tree City “program.  Over time these can--and in many communities have--grown to become regulations that not only require the conservation of tree canopies in commercial and subdivision developments, but also  creating the mechanisms that support the existence of tree lined streets.

The Purpose of a Tree Ordinance

The purpose of any tree ordinance is to establish a framework for the conservation and management of trees on public property, private property or both.

Your tree ordinance may have additional purposes that are unique to your community’s situation.  Write a succinct purpose statement for your ordinance, keeping in mind the following guidelines for what tree ordinances can do and cannot or should not do.  Note: A purpose that is not supported by enforcement language and adequate staffing can cause significant administrative problems as the ordinance is implemented.

What Tree Ordinances can and cannot do….

Tree ordinances are an effective community tree management tool because they provide standards for conservation and establishment of community trees and educate the citizens about what it takes to maintain and grow a community forest canopy. Tree ordinances may be ineffective tools when used to address issues that are not tree related. Sometimes, in the process of developing a tree ordinance, development team members express frustration with current land use regulations ( parking lot size, building setback widths, structure footprints, impervious surfaces, etc). These issues are not tree issues. They are land use regulation issues that need to be addressed elsewhere in the development or zoning code. Tree ordinances need to be about trees.

Tree ordinances can:

  • Help conserve natural, forested areas for the benefit of the community and environment
  • Require a minimum amount of tree density on developed and undeveloped sites
  • Regulate the conservation and planting of trees during land development
  • Regulate the removal and conservation of trees of special value to the community
  • Make immediate, visible changes to the landscape
  • Promote the utilization of trees for the many beneficial functions they provide
  • Require canopy over impervious (paved) surfaces such as streets and parking lots
  • Set standards for tree conservation, planting, maintenance and protection
  • Set establishment standards that improve the quality and health of the tree population
  • Establish standards for utility line clearance pruning
  • Provide added protection of public health, safety and welfare by reducing tree risk
  • Provide flexibility in achieving community tree management goals

Tree ordinances cannot (or should not):

  • Stop or prevent development that is allowed by zoning regulations
  • Stop or prevent a removal of trees that is allowed by the development code
  • Reduce the amount of impervious surface allowed on a site
  • Save every tree
  • Require more trees on a site than will sustainably fit in the available growing space
  • Eliminate the need for pruning branches and removing trees around building infrastructure
  • Stop utility line clearance pruning
  • Eliminate all risk posed by trees in the public landscape
  • Take into account all conditions and situations on every site
  • Be successfully implemented and enforced without adequately trained staff, time and budget

Types of Tree Ordinances


Determining the scope of your tree ordinance is one of the first decisions you will make in your development process.  It will guide you in choosing the appropriate components to include.  It will also help to determine where your tree ordinance should be placed within your community’s code of ordinances.

Tree Ordinances Applied to Public Property

Public tree ordinances only regulate and protect trees on public property.  These ordinances may also include statements addressing the need for landowners to appropriately manage trees on private property that pose a risk to public health, safety and welfare, in a timely manner.

Public tree ordinances can provide a framework for how public trees will be managed within a community by clearly stating:

  • Community forest management vision and goals;
  • Purpose and intent of public tree management and the tree ordinance;
  • Value and benefits of public trees and community trees in general;
  • The community’s authority to maintain public health, safety, and welfare by planting, pruning, maintaining, and removing public trees;
  • Establishment of tree board, including number of voting members, member categories, and the roles and responsibilities of the tree board;
  • Commitment to participating in the Tree City USA program and holding an annual Arbor Day celebration
  • The responsibility of private property owners to mitigate the risk posed by their trees to public health, safety and welfare, through timely removal or risk reduction.

Tree Ordinances applied to Private Property

Private tree ordinances regulate trees on private property – either commercial or residential or both (often called “Comprehensive” Tree ordinances).  Most typical private tree ordinances regulate trees on commercial property at the time of development. This regulation is also sometimes applied to multi-family residential developments and Planned Unit Developments (PUD’s) since their density usually results in them being treated as commercial properties. Some ordinances will have regulations that apply only to downtown, historic, or special “overlay” districts. Other ordinances may also regulate tree removal and replacement on developed private property, either residential or commercial. Some of these regulations stratify the application of the tree ordinance based on the local zoning code and the idea that some land area zonings are more conducive to tree conservation.

Comprehensive Tree Ordinances

Tree ordinance that apply to both public and private property trees are usually referred to as “Comprehensive Tree Ordinances”.  They usually include development standards, provisions for tree conservation and regulations that apply to all forms of property ownership.  These ordinances sometimes exempt single family residential properties from tree removal restriction of trees that are not in a shared right-of-way or easement. The more inclusive of these ordinances address all the trees in the community within city boundaries.

Tree Ordinance Methodologies

There are a variety of ways communities attempt to conserve or require replacement of trees in their development codes. 

But First…a bit of Georgia Tree Ordinance History by: Joe Burgess

Early tree ordinances functioned as tree replacement ordinances, i.e., a tree removed required a tree to be planted.  As ordinances evolved, many changed to using an “inch per inch” caliper replacement arrangement, and then to a “basal area inch per basal area inch” (cross sectional area of a tree usually at 4.5 feet above the ground) replacement scheme.  However, this methodology wasn’t achievable on development sites where there was no place to plant all those trees. A partial solution was to pay the local government a fee for each caliper or basal area inch of tree that could not be placed on the site.

Some communities increased the required minimum number of trees to be placed or conserved on a site as a way to restrict tree removal. This gave rise to Community Tree Banks, where fees were channeled into a Tree Fund to be used exclusively for planting trees on public property as part of a “mitigation” requirement. As development in some growing communities increased, the Tree Funds increased, and some communities (oftentimes under complaint) tapped into those monies to fund non-tree issues, and additional problems resulted.

Once urban forest research began to show that tree “canopy” (read shade) was what should be conserved to increase all tree benefits, tree canopy ordinances became more common.  Communities worked within their existing zoning codes to mandate a minimum percent of tree canopy per site, either to be preserved or to be planted for a future “credit”. The benefit to this was that it was easy to measure shade area (often from an aerial photograph) to determine if the minimum was met. If an owner or developer didn’t want to maintain or plant at the minimum level, they could pay a “fee in lieu of canopy”.

A canopy ordinance with such minimum shade requirements comes with its own issues related to credit and responsibility for property line trees and boundary trees.

The latest trend in tree ordinances is performance based and focuses on the amount of open soil surface area (OSSA) that trees need to become sustainable in the landscape.  This approach ensures long-term conservation of tree root systems by matching available planting spaces to the space needed by a growing tree. It should also help reduce the amount of overplanting, or shoehorning, of trees into a development site, and it should protect the growth of the future canopy.

Ordinance Types

There are basically four different approaches to managing trees on private property that are used most often when land development is involved. Those approaches include but are not limited to:

  • Tree replacement
  • Tree density minimums
  • Tree canopy minimums
  • Sustainable spaces

1. Tree Replacement Ordinances

Early forms of tree ordinances involved the replacement of, rather than conservation of, trees that were removed. Tree replacement ordinances commonly required “one for one” replacement based on either number of trees removed, the diameter size of trees removed, or the basal area lost.

2. Tree Density Minimum Ordinances

Tree ordinances based on density minimums require a specific threshold of tree conservation or replacement. That threshold is set in the tree ordinance and is, in theory, the community’s decision of the appropriate number of or size of trees that should remain after development. Existing trees that are to remain on site usually receive a credit equal to the sum total of their basal areas.  If the minimum density required by the ordinance is not met, then enough trees must be planted to bring the site into compliance.

Trees that are replanted on site are generally given a density credit based on their future expected basal area, based on species and usually calculated at 15 years of growth. The schedule of appropriate credit for replacement trees can vary widely, and extra density credit may be given as a way to preserve trees considered specimens or trees that are historically significant.

Under some tree ordinances, removal of these particular special trees triggers a requirement for increased density, sometimes without regard for the available space on site to plant more trees. Rather than overplanting in such a situation, developers must contribute to the Tree Bank fund that will be used to plant trees on public property.

3.  Tree Canopy Minimum Ordinances

Tree canopy is the portion of a tree that provides shade, and shade provides most of the benefits we enjoy from trees.  Some tree canopy ordinances set a minimum of shade or canopy that each site must maintain. These minimums are often stratified by different zoning types, i.e., a light density office development would have a higher minimum canopy requirement than a heavy industrial site would have. The calculation is usually simply done using “leaf on” aerial imagery. For example: a 4-acre multifamily development that is required to have 25% canopy coverage would need to either preserve 1 acre of shade at the site or plant trees to reach the required minimum. When calculating how many trees must be planted, a schedule of expected future canopy size as determined by species is used. Usually a community-wide schedule of required canopy percent is generated, and many communities “grandfather in” residential developments that either are over a minimum acreage or those that existed before the tree ordinance was passed.

4.  Sustainable spaces tree ordinances

This kind of tree ordinance protects trees by requiring a minimum amount of open soil surface area (OSSA) that is needed for a tree to mature to the point that its full benefits and character are realized. This is an improvement over current tree ordinances that do not set soil minimums, which can result in planted trees rarely living to maturity and conserved trees frequently not remaining in the landscape long term due to root zone damage. 

The OSSA calculations are based on research data that shows a minimum of 640 square feet of OSSA is required for every 1 square foot of tree basal area. Such an ordinance requires a development perspective that is different than what we commonly see: a blueprint design that shows large trees growing in small spaces. For example: A housing development might be required to not only have a certain amount of contiguous OSSA but also be required to replant or conserve existing trees based on the minimum OSSA that is needed, according to species, to reach maturity.

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