Urban Forest Issues
27 August 2007
Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580 fax: 434.872.4578
The U.S. population has grown increasingly urban each decade, from 28 percent in 1910 to 80 percent in 2000. In the Chesapeake Bay watershed alone, residential development is predicted to consume 800,000 acres between 2003 and 2030, nearly 90 percent of it replacing farmland. As urban communities grow larger and faster than ever before, natural resource management in these areas becomes crucial for achieving sustainable development and maintaining and enhancing the quality of life and the environment.
Many tree-care issues affect the use, management, and protection of the urban and community forest. These include loss of tree cover, proper care of trees to increase longevity and decrease hazards, alleviation and prevention of soil compaction, providing for better wildlife habitat, the effect of air pollution on tree health, and public mandates for storm-water retention and flood prevention.
The loss of tree cover is becoming a critical issue in many areas. In a natural or commercial forest situation, the canopy will approach 100 percent cover as trees attempt to capture all available sunlight. In a residential area, the canopy cover will typically range from 30 percent to 60 percent. Highly developed areas often have less than 10 percent canopy cover.
Planting the right tree in the right place is essential to the proper care of trees. Trees can only provide benefits if they are healthy and live for a long time. Trees should not be planted where they cannot live or will interfere with power lines or buildings. They should not be planted where they cannot survive cold winters or hot summers because they will die and have to be removed. These are examples of trees costing money, not saving money.
Pruning is sometimes required for the proper care of trees. In young trees, you prune primarily to promote good tree structure. Older trees may require periodic pruning to clean out dead and dying branches or for other clearly defined reasons. However, a good rule of thumb is never to remove a branch from a tree unless you have a clearly defined reason for doing so. When you prune, properly placed, clean cuts will help the tree recover quickly. A common mistake is to remove a tree limb by cutting it flush with the tree trunk. Take care to cut the branch at its natural removal point, the branch collar. Remove any size tree limb with three cuts to avoid bark stripping from the tree after the final cut. Perhaps the worst mistake you can make is to top a tree. This is the practice of severely cutting back branches and the main stem so that only stubs remain. Topping destroys the natural beauty of a tree and makes it dangerous by allowing decay fungi to invade the branches and make them hollow. Although strong limb growth may occur after topping, these branches are only weakly attached to the outer layers of wood and are likely to fail in storms.
Many people forget to protect the roots of trees in an urban area. In a natural forest situation, the forest floor is usually left undisturbed in the area beneath a tree. This often is not the case in the urban/community setting, where tree roots are restricted by pavement and building foundations. In 2003, Hurricane Isabel uprooted many trees because their root systems had been compromised by sidewalks, curbs, and streets.
Soil compaction is a problem in every community. It occurs when vehicles, particularly those involved with construction and maintenance, drive across moist soil, but it can even occur where there is heavy foot traffic. Natural, undisturbed soils have many pore spaces that are important reservoirs of gasses, such as oxygen, and moisture that roots need to live. Pore spaces also serve as passageways for water to percolate through the soil profile. When compaction occurs and these spaces collapse, existing roots find it difficult to obtain oxygen, nutrients, and moisture, and the resultant dense soil is difficult for new roots to penetrate.
On October 19 Cooperative Extension presents Its All About the Trees, a training session geared toward arborists and landscape maintenance people on tree care. ISA, VNLA, and commercial pesticide applicator credits will be given. Please call 872-4580 for more information.
For more information about this and other landscape topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.