Guidelines for Developing and Evaluating Tree Ordinances

Goals for community forest programs

Goals are central to developing an ordinance. Goals provide the basis for formulating and evaluating the management strategy and any tree ordinance that results from it. Thus, selecting appropriate and meaningful goals (step D) is crucial to the success of the entire process. The goals described below are consistent with good urban forest management and are typical for municipal tree programs, but this list is not comprehensive. (If you would like to see additional goals treated here, please contact us.)

The goals described here are also specific enough to allow for evaluation. There is little point in establishing a goal if there is no practical way of determining whether progress is being made towards realizing that goal. To answer the management questions "Are you getting what you want?" and "What do you have?", you will need to evaluate tree resources, management activities, and public attitudes. Evaluation methods are important tools for formulating and monitoring tree management strategies and monitoring ordinance performance.

A variety of approaches can be used to help attain any given goal. You will need to decide which approaches are most appropriate for your own community. If the goal is to be addressed through a tree ordinance, one or more ordinance provisions may apply. For each goal listed below, we have included links to specific ordinance provisions that can be used to address that goal. We also describe and provide links to evaluation methods that can be used to evaluate progress towards each goal.

Possible tree program goals:

1. Establish and maintain maximum tree cover.

The urban forest serves a wide variety of functions that promote the health, safety, and general welfare of residents. These functions include: All these benefits increase as canopy cover increases. By establishing and maintaining maximum tree cover, the community is able to realize the maximum benefits the urban forest can provide. The maximum amount of tree canopy a given community can support must be determined by analyzing limitations posed by climate and land use.

Ordinance provisions

Tree ordinance provisions covering planting, maintenance, and removal of trees on public and private land are related to this goal. Performance standards for the amount of tree cover the community hopes to achieve and maintain along streets, parking lots, residential and commercial areas, parks and open spaces should be established in these provisions. A provision calling for development of an urban forest management plan is essential to this goal. This plan should provide for a sustained forest canopy through properly phased tree planting and removal. Specific provisions:

Evaluation methods

Tree canopy cover is one of the most basic and useful descriptors of the urban forest. Simply put, it is the percentage of land area covered by tree canopies. By periodically measuring canopy cover, communities can assess the effectiveness of ordinances and other management methods aimed at maintaining or increasing tree canopy.

Canopy cover can be measured directly, through photogrammetry (measurement from aerial photographs or digitized aerial images) or ground surveys. These methods can be relatively easy to use, and do not necessarily require expensive equipment. Tree density, the number of trees per unit area, is indirectly related to tree canopy cover. Tree density can also be used to estimate tree cover, if the average canopy spread per tree is known. Tree density can be calculated for areas that have a complete tree inventory.

2. Maintain trees in a healthy condition through good cultural practices.

A community is not likely to realize most of the benefits that the urban forest can provide if its trees are in poor health. Promoting tree health helps communities protect their investment in the urban forest. Public health and safety also depend on healthy trees. Improperly maintained and unhealthy trees often have an increased risk of breakage or failure, which can result in personal injury and property damage.

Cultural practices have a major impact on the health of urban trees. Proper and timely pruning can promote good tree structure and health, whereas topping and other improper pruning techniques can result in hazardous structure and decay. Irrigation is necessary for tree survival in many situations, but excess or improper irrigation practices can contribute to the decline of established trees. By providing for proper tree care and eliminating destructive practices, communities can go a long way toward maintaining their urban forests in a healthy and safe condition.

Ordinance provisions

Tree ordinance provisions related to this goal include those that regulate tree maintenance practices (such as pruning) and prohibit or regulate various activities that may harm trees. Management of specific disease or pest problems, such as Dutch elm disease, may be facilitated by provisions that limit species selection, require removal of diseased trees, or authorize other pest management measures.

Specific provisions:

Evaluation methods

Progress toward this goal can be evaluated by assessing tree health over time through ground surveys or by record keeping. Community tree inventories that include health ratings may contain all of the data necessary for evaluating progress toward this goal. Otherwise, sample plots can be established to obtain data on tree health and/or improper or prohibited cultural practices. For example, jurisdictions that prohibit topping might survey specifically to determine the incidence of this particular problem. For certain health problems affecting large areas with many trees, remote sensing methods (e.g., color infrared photos, multispectral satellite imagery) may be useful.

3. Establish and maintain an optimal level of age and species diversity.

The trees that make up the urban forest have finite life spans and must be removed as they die. Living trees may also be removed when their health, appearance, or structural integrity decline substantially, or when they conflict excessively with utilities and structures. The likelihood that a tree will need to be removed for one reason or another increases as the tree grows older and larger. If areas are planted to a single species at one time, a large percentage of the trees will need to be removed over a short time period when they reach the end of their useful life. This results in a rapid reduction in canopy cover, and the loss of many of the benefits provided by the urban forest. This undesirable situation is less likely to occur if the urban forest is composed of a variety of tree age classes and species.

Serious pest outbreaks and epidemics can arise in communities in which large areas are planted to a single susceptible species or variety. These outbreaks can seriously impair the overall health, appearance, and longevity of the urban forest. Species diversity and genetic diversity within species helps stabilize the urban forest by buffering it from pest and disease epidemics. Many insect pests and plant pathogens can only attack one or a few tree species. The reproduction and spread of many tree pests and diseases will be slowed if the community forest contains a diverse mix of tree species. Furthermore, if an especially virulent disease or pest problem does develop on a given species, species diversity ensures that the condition of the entire community forest is not jeopardized.

Ordinance provisions

The ordinance provisions that most directly address this goal require the development of and adherence to a complete urban forest or street tree master plan. To address this goal, the plan should provide for species diversity in new tree plantings, a significant change from single species blocks that are common in many communities. The master plan should also describe how removal and replanting throughout the community can be phased to attain a good mix of tree maturities.

Specific provisions:

Evaluation methods

In order to evaluate progress toward this goal, information is needed on the distribution of tree species and age classes within the urban forest. For public trees, this information can typically be extracted from a good quality tree inventory. For community trees that are not listed in a tree inventory, this information can most readily be obtained through a ground survey. Accurately determining tree age may not be possible, but for the purposes of evaluation, it will usually suffice to group trees into broad age classes.

4. Promote conservation of tree resources.

The benefits derived from the urban forest generally increase as tree size and canopy cover increase. Therefore, it is in the best interest of the community to protect its existing tree resources from loss or depletion. It is not possible to indefinitely preserve individual trees, since each tree will eventually die. However, it is possible to preserve both the urban forest and natural woodlands by restricting the indiscriminate removal of trees in all age classes, and by making provisions for natural or human-assisted regeneration. This embodies the concept of conservation.

Ordinance provisions

Many jurisdictions have attempted to address this goal with provisions that require approval to remove certain classes of trees under certain conditions. Unfortunately, in focusing solely on the "preservation" of individual trees, conservation of tree and forest resources is often overlooked. For instance, some ordinances have focused on protection during new construction, but make no provisions to ensure that trees will receive proper care or be retained after construction is completed.

In areas with native tree resources, ordinance provisions that address this goal should conserve stands of trees rather than only individual tree specimens. They should prevent depletion of the tree canopy over both short-term and long-term time horizons. Finally, they should set basic performance standards for the amount of tree canopy to be retained or achieved. Provisions related to the development of a master plan, and those regulating tree planting, protection, and removal are most directly related to this goal.

Conservation of tree resources alone may not be sufficient to address situations that require a more comprehensive resource management perspective. When jurisdictions seek to conserve functional forest and woodland ecosystems, such as in wildland parks or open spaces, the scope of management may need to be expanded. Other components of the plant community, wildlife, natural processes such as fire and flooding, and human land uses may also need to be considered.

Specific provisions:

Evaluation methods

If the approach used to attain this goal involves tree protection or "preservation", it will be necessary to have information on the long-term survival and condition of individual trees. If woodland or forest conservation techniques are applied, the extent, composition, and condition of stands of trees should be documented. Both aerial and ground level photography provide a simple means for documenting the presence and condition of individual trees and stands of trees over time. Ground survey methods and inventory data can also be used to provide more detailed base line data against which change can be measured.

5. Select, situate, and maintain street trees appropriately to maximize benefits and minimize hazard, nuisance, hardscape damage, and maintenance costs.

Trees and structures, such as pavement, sidewalks, and curbs (collectively referred to as hardscape), are closely associated in street tree plantings, and this is frequently a source of problems for both. Many tree maintenance and hardscape damage problems that occur in street tree plantings result from incompatibility between the planting site and the tree species. Street trees are often placed in woefully small planting spaces, resulting in premature tree decline and/or hardscape damage. Conflicts with overhead or underground utilities and damage to hardscape arise where:
  • tree species are not selected with proper attention to site limitations,
  • planting sites are not designed to provide a hospitable environment for tree growth,
  • hardscape, utilities, and structures are not properly engineered to withstand impacts associated with nearby trees.
Inappropriate tree selection is often the underlying cause for trees that become hazardous, are prone to breakage, or develop recurrent pest or disease problems. Inadequate planting sites are often responsible for poor tree growth and survival and excessive hardscape damage. By identifying and subsequently avoiding undesirable tree species, inadequate planting site specifications, and inappropriate tree-site combinations, it is possible to minimize problem situations and their high maintenance costs.

Ordinance provisions

Ordinance provisions related to this goal empower the tree authority to set and modify standards for tree selection and planting sites. This goal is normally also addressed in the development of a comprehensive management plan.

Evaluation methods

To evaluate progress toward this goal, we need information about the types of tree/site combinations that result in high maintenance costs or damage. Ground surveys can be conducted to determine what types of tree/site combinations are associated with current maintenance and damage problems. Most or all of this information may already be on hand in cities with tree inventories that track tree maintenance. Costs of hazardous tree removals, tree-related sidewalk repairs, and maintenance should be tallied by the types of tree species and planting situations where they are incurred. In the absence of good historical records, ground surveys can be conducted to determine what types of tree/site combinations are associated with current maintenance and damage problems. Once these relationships are established, they can be used as a basis to evaluate current tree selection, siting, and maintenance practices. The evaluation should be repeated periodically to account for changes that result as new species, planting methods, and hardscape designs are adopted, and as trees planted at different times mature.

6. Centralize tree management under a person with the necessary expertise.

Due to the wide variety of situations that can impact trees in the urban environment, tree-related issues may arise in a number of different municipal departments. In many jurisdictions, street trees are the responsibility of public works, while park trees are cared for by the parks department (Bernhardt and Swiecki 1989). In addition, projects approved by the planning department and work performed by the public works department often impact current or future tree resources. Utility companies, tree service firms, and private citizens are also involved in tree maintenance and removal, and some of these activities may be regulated by various municipal departments. Effective implementation of tree ordinances is likely to be hampered when responsibilities are split between different departments without overall coordination.

Unless all activities that affect trees are coordinated, departments may unintentionally undermine each other's efforts to conserve tree resources. For example, the planning department may require that certain trees be protected and maintained during development. Without coordination, the same trees might be seriously damaged by trenching for underground utility work approved through public works.

To facilitate the coordinated management of urban forest resources, it is desirable to have a single person responsible for all tree-related issues. To be effective, this position should serve as a clearinghouse for information on activities that may affect trees. The position should also have authority to approve, deny, or condition any activities in accordance with the jurisdiction's management plan, policies, and ordinances. Clearly, the person in this position should have the technical background appropriate for this complex job. Many jurisdictions do have a community arborist or forester, but this position often lacks sufficient authority to effectively manage the urban forest.

Although small communities may lack the funds for a full-time tree specialist, many of the administrative functions of the community forester may be filled by a tree board or commission. The necessary technical input may be obtained from public or private sector tree specialists. Alternatively, several smaller communities might band together to arrange for a shared "circuit riding" urban forester.

Ordinance provisions

Ordinance provisions that establish the responsibilities, authority, and qualifications of the municipal tree program manager relate directly to this goal. Other related provisions direct how coordination between municipal departments is to be established for operations that may affect trees. Evaluation method

Municipal records of tree-related permits and maintenance can provide data which show whether this goal is being realized. If tree management is truly centralized, these records should show that all activities that may affect community tree resources have been reviewed and approved by the municipal arborist or forester. Ground surveys, photogrammetry, and photo points may also be used to document situations in which a lack of coordination has led to unintended or unauthorized tree damage or removal.

7. Promote efficient and cost-effective management of the urban forest.

Financial resources are in short supply in many local governments. Even though tree care involves less than 1% of the total operating budget of most U.S. cities (Bernhardt and Swiecki 1993, Tschantz and Sacamano 1994), economic realities dictate that all municipal programs strive for efficiency and cost- effectiveness.

To operate efficiently and ensure that resources are directed toward the most critical activities, a tree program must have a clear set of priorities and a long-range plan. Although short-term savings may be achieved by deferring tree maintenance, long-term costs will be lowest when resources are spent on preventing problems rather than dealing with them after the fact. For example, a program of early and regular tree maintenance helps prevent later, more costly problems and prolongs tree longevity. Investments in time and money at the time of installation on high quality plant materials and proper site preparation will pay off in terms of tree health and low maintenance costs. Problems arising from poor site designs, defective or diseased planting stock, and improper installation procedures are typically difficult and costly to correct. Similarly, a small investment in the proper pruning of young trees will head off many structural problems that would otherwise develop and require more expensive pruning or tree removal.

Ordinance provisions

This goal is addressed in provisions that spell out the responsibilities of the tree program manager. These responsibilities should include short- and long-range planning for the tree program, setting maintenance priorities based on long-term benefits, and tracking maintenance costs. Many of these aspects would also be addressed in provisions related to the urban forest management plan.

Evaluation methods

Records on costs and the types of operations performed are used to determine the cost-effectiveness and efficiency of the urban forest management program. An accounting of labor and materials expenses should be maintained, preferably broken down by the types of activities performed, such as tree planting, pruning, and removal. Time devoted to other aspects of the tree management program should also be tracked. Activities such as planning, ordinance enforcement, research, public outreach, and education, are all important to urban forest management. Overhead costs and time should also be tracked and scrutinized, because these costs can have a major influence on the cost efficiency of the entire program.

If work records do not contain sufficient detail to track activities, data can be collect through auditing a representative sample of work days or other measurement units. Data on the amount of time required to complete various tasks may be self-reported or tracked by an observer.

8. Foster community support for the local urban forestry program and encourage good tree management on privately-owned properties.

To achieve urban forestry goals, the local government needs the support of the citizens in the community. In most jurisdictions, the overwhelming majority of the trees which make up the urban forest are on private property. For all practical purposes, the care of these privately-owned trees is up to the residents of the community. A local government cannot completely control tree management on private lands, but it can take steps to promote proper management of privately-owned trees. Educational and incentive programs are positive ways to encourage good tree care within the community.

It is important that local citizens understand the relationship between urban forestry goals and specific actions taken to achieve these goals. Otherwise, support for the overall program goals may not translate to support for the program itself. Programs to educate citizens about, and involve them in, the local urban forestry program will help increase public support and interest in the program. Voluntary compliance with tree ordinances is likely to be improved if citizens understand and agree with the management approaches implemented through the ordinance.

Ordinance provisions

Provisions that address this goal include those calling for the formation of a citizen tree commission and the establishment of educational and other outreach programs. Conducting such programs may be the responsibility of either the tree program manager or the tree commission. Incentive programs, such as those providing for cost-sharing, grants, or loans for tree planting or maintenance, are also related to this goal.

Evaluation methods

There are two distinct aspects to this goal, so evaluating progress requires two different types of methods. The first aspect involves changing the way that people think about the urban forest. Public opinion polling methods provide the best means to measure changes in public attitudes and knowledge. The process of assessing public attitudes can also serve an educational function in itself, by helping to keep urban forestry issues in the public eye.

Beyond determining what people think, it is also necessary to know if new knowledge or attitudes are translated into action. For instance, if a city decides to use public education to discourage tree removal on private property, it is not enough to know whether public attitudes about this practice have changed. Success is measured by the degree to which changed attitudes result in a decreased incidence of tree removal. This requires the use of techniques that measure the extent of tree resources on private lands over time, including photogrammetry and ground survey.

9. Facilitate the resolution of tree-related conflicts between citizens.

Trees sometimes become the focus of conflict between property owners when they obscure scenic views or keep sunlight from reaching solar energy collectors. Such conflicts may become important where property values are related to specific views (e.g. ocean or lake views). It can be helpful to set up a mechanism by which such conflicts may be resolved with a minimum of impact to the community's tree resources.

Ordinance provisions

This goal is addressed through a special set of provisions establishing a mechanism for resolving disputes over trees which obstruct light or views. The provisions covering this goal may be included in the tree ordinance or enacted as a separate view or solar access ordinance.

Evaluation methods

The effectiveness of the conflict resolution process is the primary issue in evaluating progress toward this goal. The first question to be answered is whether the process is being utilized to resolve tree-related disputes. This information can be easily obtained from records filed through the system that is established.

Assuming that the process is being used, the next question is whether the process works. This question has to be answered by those who have used the process. Extreme care must be taken to separate reactions to the outcome of the process from reactions to the process itself. It is not reasonable to expect that all parties involved in conflicts will be entirely happy with the eventual resolution. However, if the process is serving its purpose, participants should perceive it as useful and helpful. Carefully-designed polling procedures and/or follow-up interviews with process participants can be used to rate the effectiveness of the conflict resolution process.