Credit: Shawn McMahon
Using cabling to improperly support branches led to the girdling and eventual death of this tree.
An urban forest is the sum of all trees on public and private land in a given municipality. The management of an urban forest rests on the same general requirements as that of a “traditional” forest—water, space, nutrition, and sunlight.
Yet while smaller in scale, urban forestry tends to be more complex because its trees are close to people and property. Forced to interface with roadways, sidewalks, and buildings, the trees in an urban forest compete for space with everything that defines an urban environment.
Why invest in an urban forestry program? Concerns for the safety of citizens and their property most often motivate a town, city, or county to develop an urban forestry program. Falling limbs can cause traffic accidents or personal injuries, triggering costly lawsuits. Trees in intersections can obstruct drivers' views. Destructive root systems can damage buildings and other structures. Trees susceptible to windthrow—the uprooting and felling of trees due to wind—can cause property damage to the roofs or windows of surrounding buildings. Given the financial impacts, safety concerns are typically the strongest selling point for an urban forestry program.
But there are other reasons. In towns where tourism is a major aspect of the local economy, investing in urban forestry can make the community more aesthetically pleasing to visitors. Any community that is interested in building its tax base by bringing in commerce and improving demographics should consider an urban forestry program as a way to preserve and enhance the overall experience of its residents.
Finally, an urban forestry program can reduce pollution and conserve heating and cooling costs. Unlike concrete and glass, trees help diffuse light and heat, contributing to the natural energy management of the buildings they shade. In addition, trees absorb carbon dioxide and lock it in solid form (wood), improving air quality. Many city ordinances require businesses to replace trees that have been uprooted for new construction to maintain the “green” quotient. These requirements can be met either by replanting on the same property or paying into a fund that will plant trees on public land.DEVELOPING AN ORDINANCE
A tree ordinance is the set of regulations underlying any urban forestry program. It should be flexible enough to meet the needs of the community and set good policy that can be backed by law. Before drawing up such a document, it is important to put together an inventory of all of the trees in the public landscape. This database shows where the trees are located, their species, their condition, and if they are in a place that might present a problem.
Global positioning systems can be helpful, but collecting the data involves a lot of footwork. Students majoring in natural resources at a nearby university are ideal candidates for such a project. They have the necessary knowledge or can quickly be trained by an on-staff arborist or consultant. In addition, they are a cost-effective resource because they can be compensated at least partially through college credit and practical work experience. If no such resource is available, a professional consulting firm can be engaged. It is important to complete a tree inventory quickly enough to make sure the condition of trees surveyed early does not change by the time the survey has been completed.
Based on the assessment of the urban forest, a tree ordinance can be developed that ensures preservation of existing vegetation, development of more desirable vegetation, or a combination of both. Most ordinances list the desirable species for specific locations such as roadsides, parks, sidewalks, and buildings, including height and width requirements. For example:Trees planted near roadsides should have maximum height and width requirements and a non-invasive root structureTrees in parks should provide maximum shade, high resistance to disease, and high structural stabilityIdeal plantings near sidewalks include trees with a limited root structure and high disease resistanceTrees near buildings should follow maximum height and width requirements and offer structural stability.
In addition to addressing safety and maintenance concerns, a tree ordinance also can help gradually eliminate invasive and non-native species, even on private property. It is important to keep in mind the life cycle of potential nuisance species. Many have specialized adaptations, such as indigestible seeds that are easily dispersed by wildlife and can quickly spread to replace the native vegetation. Tree ordinances can require private individuals to remove nuisance species or diseased trees from their land, as in cases of trees infected with citrus canker that present a hazard to industry or commerce.GET THE PUBLIC INVOLVED
The initiative for an urban forestry program is generally administered from within the building and zoning department. Public support is essential to the successful adoption and implementation of a program.