Why Plan for Forest Management?
Human activities have dramatically altered the landscape of the U.S over the past 400 years. While conversion of forest land for agricultural use was a primary cause of forest loss over this time period, the rate of forest conversion for urban uses has greatly increased more recently, reinforcing the need for greater integration of forest and land use planning. American Forests estimates that tree cover in urban areas east of the Mississippi has declined by about 30% over the last 20 years, while the footprint of urban areas has increased by 20%. In fact, tree canopy cover in urban and metropolitan areas across the U.S. averages only 27% and 33%, respectively (Dwyer and Nowak, 2000).
As land within a jurisdiction is developed parcel by parcel, formerly continuous forests are divided into smaller patches. This is referred to as forest fragmentation. As forests are divided into smaller fragments, the proportion of edge to interior habitat increases, creating an “edge effect.” Edge habitat occurs at the boundaries between different types of land cover, while interior forest habitat is defined as large tracts of continuous forest cover. Fragmentation diminishes habitat for forest interior dwelling species, although the amount of interior forest habitat needed varies for different species. In general, habitat quality declines in response to the size of the forest fragment. Urban sprawl aggravates forest fragmentation and may also lead to drought.
Interior forest (left), forest fragment with increasing edge habitat (center), small forest patches resulting from fragmentation (right) (graphics courtesy of University of Connecticut Center for Land use Education and Research)
As the loss of trees and forests in developing areas continues, the network of trees and forests in existing urban areas also deteriorates due to removal, lack of replacement and decline in health. In fact, American Forests estimates that the average life expectancy of a downtown urban street tree is just 13 years. This is due to factors such as limited soil availability, poor soil quality, lack of water and increased temperature. Urban forests tend to have very different characteristics than their rural counterparts because of the stresses placed upon them by the often harsh urban environment. Stressors such as air pollution, illegal dumping, competition from invasive species, and impacts from deer overpopulation can result in forests that have little understory, are dominated by trash and invasive plants, are highly fragmented and provide little valuable habitat or other functions.
The typical urban forest fragment has abundant invasive plants (e.g., kudzu), little understory, numerous gaps in the canopy, and is often used by neighborhood residents as a yard waste dumping ground
Since the 1980s, urban forest research and new technical analysis tools have defined a wider role and value for urban trees. There is greater recognition of how urban trees and forests improve air and water quality, protect drinking water supply, reduce stormwater runoff, conserve energy, and protect public health. Increasingly, these benefits are being better defined and quantified through scientific research. The projected increase in development over the next three decades reinforces the need for better forest planning and management. Stein et al. (2005) project that more than 44 million acres of private forest will experience increased housing development by 2030. Click here for a more detailed breakdown of the projections for specific states. Local jurisdictions and states can plan and target efforts to prevent or reduce conversion of their most valuable forest lands and to maintain large tracts of healthy forests.
What Forest Planning Efforts are Underway?
Major initiatives to incorporate forest assessment and management into planning efforts include urban tree canopy assessment and goal-setting at the jurisdictional scale (e.g., counties, towns), and incorporation of forest assessment and management into watershed planning efforts. Both of these forest planning methods include making an assessment of the existing resource, setting a numerical goal or target, developing and implementing a plan to reach the target, and tracking progress over time. The major differences between the two approaches are the scale at which they are conducted (jurisdiction versus watershed) and the element being measured (forest cover versus forest canopy).
A watershed is an area of land that drains to a particular waterbody, such as a lake, estuary or point along a river or stream
Urban tree canopy assessments are typically conducted for an individual jurisdiction or metropolitan area, while urban watershed forestry tracks forest cover at the watershed scale. A watershed is an area of land that drains to a particular waterbody, such as a lake, estuary, or point along a river or stream. Managing forests at the watershed scale is important because forests, particularly healthy ones, contribute greatly to the health of a watershed by:
- Reducing stormwater runoff and recharging groundwater
- Improving regional air quality
- Reducing stream channel erosion
- Improving soil and water quality
- Providing habitat for terrestrial and aquatic wildlife
- Reducing summer air and water temperatures (as a result of stream shading)
The benefits of interest are a little different when evaluating urban tree canopy for a jurisdiction as opposed to a watershed because some of the benefits of forests are more apparent at the community, neighborhood or parcel scale. Trees:
- Increase livability
- Improve health and well being
- Block UV radiation
- Provide shade
- Buffer wind and noise
- Increase recreational opportunities
- Provide aesthetic value
- Reduce urban heat island effect
- Positively influence consumer behavior
- Increase property values
- Decrease heating and cooling costs
Watershed-scale forest assessments typically focus on measuring forest cover, which is the total area of land, urban or rural, that is classified as forest. In urban areas, trees may be found growing individually, in small groups or under forest conditions. Therefore, the best measure of urban forest cover is attained by mapping the urban tree canopy, which is the layer of tree leaves, branches and stems that cover the ground when viewed from above. While measuring urban tree canopy generally gives a more accurate representation of the extent of trees and forests in an urban watershed than measuring forest cover, the assessment approach used by a community will be driven by the funds and technical capacity of the staff as well as the availability of data.
References
Cappiella, K., Schueler, T., and T. Wright. 2005. Urban Watershed Forestry Manual. Part 1: Methods for Increasing Forest Cover in a Watershed. NA-TP-04-05. USDA Forest Service, Northeastern Area State and Private Forestry. Newtown Square, PA.
Dwyer, J.; Nowak, D. 2000. A national assessment of the urban forest: an overview. Proceedings of Society of 1999 American Foresters National Convention, Portland, OR.
Stein, S.M., McRoberts, R. E., Alig, R. J., Nelson, M. D., Theobald, D. M., Eley, M., Dechter, M., and M. Carr. 2005. Forests on the Edge. Housing Development on America’s Private Forests. USDA Forest Service. Technical Report PNW‐GTR‐636.
