What is Urban and Community Forestry?

Transcription

1 What is Urban and Community Forestry? The Role of Plants: Generally, urban forests are collective masses of trees found within the boundaries of cities, towns or neighborhoods. Such forests contain publicly and privately owned trees growing in parks, near schools, within residential yards, on the grounds of institutions and along streets. These tree collections may have very different appearances. They may be remnant forests, small tracts of trees preserved during development that become a naturalistic looking greenbelt. Some sites have a designed landscape, made up of carefully placed trees and shrubs surrounded by turf, as in many urban or community parks. Some forests are on "leftover" land, an untended collection of plant volunteers and scruffy vegetation. Each of these forest settings not only looks different, but the ecological functions of each may vary. Nonetheless, scientists have proven that trees, in all settings, provide extensive environmental benefits. The Role of People: Urban trees offer an important link for connecting urban populations with natural resources. Involving residents in urban forestry activities provides an opportunity to integrate environmental stewardship with social progress. This involvement often influences citizens perceptions and behaviors concerning forests and forest conservation. Trees will sustain themselves only if they are cared for and maintained by communities of people. Many people who live in cities and towns have come to realize the many benefits and services that trees provide. Essential to the survival of urban trees are professional urban foresters, state and local governments, community leaders and citizen volunteers working together to plant, maintain, and support the cause of trees in their communities. Forest and community managers need accurate information on the urban forest resource, how it is changing, and the ecosystem services that trees provide. Decision making tools are also necessary to guide management and policies related to improving ecosystem services provided by trees. 1

2 Social scientists have demonstrated that interaction with plants and trees in urban settings produces numerous psycho-social benefits. The experience of nature: helps reduce stress and anxiety improves medical recovery and convalescence contributes to greater job satisfaction and productivity enhances quality of life. Threats to Tree Growth in Urban Environments: Space limitations or urbanization of natural, wooded areas outside of cities Poor soil quality and loss of topsoil in land development which therefore threatens healthy tree growth Exotic pest, disease and invasive plant introductions including Dutch elm disease, Asian gypsy moth and the Woolly adelgid Expansion of urban infrastructure (road widening, parking lots etc.) with resulting negative impacts on trees Increasing drought, salt pollution in the winter and air pollution problems. A lack of leadership in local and state government to lead in urban forestry awareness and efforts. Trees and Ecosystem Services Trees are indicators of a community's ecological health. While urban ecology is more complex than just tree cover, trees are good indicators of the health of an urban ecosystem. When trees are large and healthy, the ecological systems-soil, air and water-that support them are also healthy. In turn, healthy trees provide valuable environmental benefits. The greater the tree cover and the less the impervious surface, the more ecosystem services are produced in terms of reducing stormwater runoff, increasing air and water quality, storing and sequestering atmospheric carbon and reducing energy consumption due to direct shading of residential buildings. 2

3 Trees and Water Stormwater Runoff Reduction Trees and soils function together to reduce stormwater runoff. Trees reduce stormwater flow by intercepting rainwater on leaves, branches, and trunks. Some of the intercepted water evaporates back into the atmosphere, and some soaks into the ground reducing the total amount of runoff that must be managed in urban areas. Trees also slow storm flow, reducing the volume of water that a containment facility must store. For example, in the Metropolitan Washington DC region, the existing 46 % tree canopy reduces the need for retention structures by 949 million cubic feet, valued at $4.7 billion per 20-year construction cycle (based on a $5/cubic foot construction cost). Our studies show that impervious surfaces have increased by 20% over the past 2 decades in urban areas at a cost in excess of $100 billion nationally. Local governments are increasingly looking toward non-built stormwater management strategies, including trees to reduce the cost of constructing stormwater control infrastructure. Trees and Water Quality When stormwater hits impervious surfaces in urban areas, it increases the water temperature and also picks up various pollutants, everything from excess lawn fertilizers to oils on roadways. This translates into water quality problems when large volumes of heated stormwater flow into receiving waters, posing threats to temperature sensitive species, such as trout and small invertebrates, as well as providing conditions for algal blooms and nutrient imbalances. Tree cover helps intercept rainwater, thus reducing the amount, and speed, of stormwater along with filtering pollutants that eventually flow to receiving waters. The U.S. Environmental Protection Agency (EPA) regulates water quality, including those from non-point source pollutants such as stormwater runoff. As cities recognize the high costs of controlling stormwater through "gray infrastructure," they are looking for innovative ways to inexpensively install effective controls. In 2003, new Clean Water Act regulations issued under Stormwater-Phase II provide cities with opportunities to incorporate trees into specific environmental practices. 3

4 Trees and Air Quality Trees and other plants make their own food from carbon dioxide (CO 2 ) in the atmosphere, water, sunlight and a small amount of soil elements. In the process, they release oxygen (0 2 ) for us to breathe. Trees produce enough oxygen on each acre for 18 people every day. Air pollution in our cities and even our suburbs is a serious concern. The burning of fossil fuels has introduced a steady flow of deadly pollutants into our atmosphere and very few urban areas can meet national clean air standards. Luckily, we are surrounded by efficient air cleaning machines-trees. Trees remove many pollutants from the atmosphere, including nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), carbon monoxide (CO), and trees help to settle out, trap and hold particulate pollutants (dust, ash, pollen and smoke) that can damage human lungs. Trees remove gaseous pollutants by absorbing them through the pores in the leaf surface. Particulates are trapped and filtered by leaves, stems and twigs, and washed to the ground by rainfall. Air pollutants injure trees by damaging their foliage and impairing the process of photosynthesis (food making). They also weaken trees making them more susceptible to other health problems such as insects and diseases. The loss of trees in our urban areas not only intensifies the urban "heat-island" effect from loss of shade and evaporation, but we lose a principal absorber of carbon dioxide and trapper of other air pollutants as well. Trees and Carbon In addition to improving air quality, trees are able to absorb atmospheric carbon, which reduces greenhouse gases and thought to contribute to global warming. The carbon related function of trees is measured in two ways: storage, or the total amount currently stored in tree biomass, and sequestration, the rate of absorption per year. Tree age greatly affects the ability to store and sequester carbon. Older trees store more total carbon in their wood and younger trees sequester more carbon annually. While there is no current economic measurement of the value of carbon sequestration in the U.S., international markets are trading carbon today and these may also be traded in the U.S. before too long. 4

5 Trees and Energy Conservation Anyone who has ever sat under a tree on a hot summer day has appreciated the cooling ability of trees, but trees can do more than just provide shade for a picnic. Trees cool our neighborhoods in the summer and save us money on energy costs and related air pollution. American Forests has developed a method for estimating the energy conservation benefits of trees from direct shading of one and two-story residential buildings. This method is the result of research conducted by Dr. E. Gregory McPherson of the USDA Forest Service. Trees are most effective when located to shade air conditioners, windows, or walls and when located on the side of the home receiving the most solar exposure. In many parts of the country the west side is most valuable, followed by the east and south, although this ranking can change based on geographical considerations. In a study released in August 2001, American Forests found that tree cover in the metro Atlanta area saved residents approximately $2.8 million annually in reduced energy costs. In 1999, a 3.2 million acre area around Houston was found to benefit by $26 million annually as a result of the cooling effects of its tree cover. Similar trends have been found throughout the country. Indirect effects of tree shading An additional benefit of conserving energy at home with strategically planted trees, local power plants are not required to produce as much electricity, and thus emit less pollution, including carbon. In urban and suburban areas, the amount of avoided carbon output outweighs even the amount of carbon sequestered by the natural forest as it grows. Watersheds, Woodlands and Wildlife Everyone lives in a watershed. A watershed is an area of land that drains water to a common water body (called receiving water ). Humans are an integral part of the watersheds in which they live. Human activities, both in the water and on the land, can have a great impact on watershed functions. Wildlife habitats can be protected and preserved either through actions and practices that serve to support and maintain the important components of these systems. Conservation 5

6 easements, designed to protect habitats through land preservation (i.e. nondisturbance of the land), also help protect habitats. Watershed Functions: Watersheds transport the water that runs over the land and into the ground, providing many vital ecological and hydrologic functions. (Hydrology: surface water and ground water functions and behavior). Watersheds collect water from rainfall, storing some of this precipitation in wetlands, soils, trees and other vegetation, and under-ground in aquifers. The floodplain (i.e. riparian zone ) along the banks of streams also serves as an important storage system for water during periods of heavy or prolonged rain. These natural storage facilities help eliminate contaminants as suspended particles settle out and as water infiltrates into the soil where biological and chemical reactions can break down impurities. Some of this stored water eventually flows into streams, lakes and marine waters through surface runoff and as subsurface flow. And, ecologically, watersheds provide critical habitat for many plant and animal species, as well as transport paths for sediment, nutrients, minerals, and a variety of chemicals. Recommendations: Observe your land. Get familiar with where water flows (especially before clearing/building). When carrying out land disturbing projects, consider how the hydrology may be impacted and apply low impact development techniques to hold and infiltrate rainwater on your property. Maintaining and Enhancing Wildlife Habitats There are many woodland management practices that you can perform on your property to maintain and preserve wildlife habitat. Snag and Den Trees: Both snag and den trees (trees with internal cavities) provide essential nesting habitat for more than 60 cavity nesting birds and mammals. Woodpeckers and flickers excavate holes in dead wood for nests and later secondary cavity nesters, such as wood ducks and raccoons use holes for nests and dens that were created by the cavity excavators. Another important function of snags is as a food source for a large number of bird species that glean insects and other invertebrates from dead wood, bark, and fissures / cracks in the dead and dying wood. Many live trees may be classed as 6

7 snags or wildlife trees. These include trees with large broken tops and ensuing decay or have several large dead branches. Recommendations: Retain snags and cavity trees wherever possible Create snags by cutting or girdling the tree Leave fallen trees, limbs and leaf litter for foraging, nesting and den sites. Consider leaving high stumps wherever possible Travel Lanes and Wildlife Corridors Many times forested areas become fragmented due to land development and vegetation removal. Isolated woodlands can benefit wildlife if they are linked together. Some wildlife venture only a short distance from cover when feeding or nesting. Travel lanes through open fields allow wildlife to venture out a little further, so they can use more of the field. Recommendations: The wider the travel lane the better. Travel lanes should be a minimum of 20 ft. wide. Shrubs growing alongside fences form good travel lanes. Hedgerows along roads serve as travel lanes. Forest Edge: Edge habitats exist where two landscapes or habitats interface, like where a grassland field meets a forest. Edges can be classified into two types: inherent and induced. Inherent edges result from permanent features in the landscape, such as abrupt changes in soil or topography, and tend to be relatively stable. In contrast, induced edges are constantly changing because of vegetation growth and succession, and are caused by human activities such as agriculture, timber harvest, and development, or natural events such as fire, disease, insect damage, or wind throw. Some species will benefit from an increase in edge habitat and others will be influenced negatively. Wildlife generalist species, those that can reside in a variety of habitats or habitat conditions, such as white-tailed deer, are often benefitted, while habitat specialists, those that have very specific habitat requirements, such as the Piliated woodpecker, are often disadvantaged. Before physically altering landscapes, potential impacts of proposed management should be assessed for any residing sensitive species in order to understand costs and benefits that may be experienced. 7

8 Recommendations to Decrease Edge: Avoid land use practices that fragment large areas of native vegetation into small parcels. Examples include conversion of forest to introduced pasture. Control encroachment of invasive or noxious plants into grasslands and forests. Use timber harvest techniques such as selective cutting that retain forest cover. Riparian Habitats: The vegetated area with moist soils adjacent a stream is termed riparian habitat. Many kinds of wildlife use riparian woodlands. Not only do these woodlands provide food, dens, roosts, and nesting sites, they also serve as wildlife migration corridors. Trees are beneficial to the stream system. Shading the water with their canopy provides organic matter to feed aquatic invertebrates, fish and other animals. Plus root systems serve to stabilize stream banks and prevent erosion. Riparian woodlands warrant extra protection due to the diverse wildlife community that uses these areas and the need for maintaining environmental services such as water purification. Recommendations: If riparian habitat is intact, preserve a wide corridor of trees ( ft. wide, if possible) on each side of the stream. If the existing riparian zone shows disturbance of soils or vegetation, reestablish vegetation by planting seedlings (choosing fast-growing species such as cottonwood or willow), or seed from nearby trees to speed up regrowth. If the riparian area contains grasses and other low-growing vegetation, but does not contain large, woody vegetation, plant fast-growing tree species to revegetate the area. Information provided by: AMERICAN FORESTS PO BOX 2000 Washington, DC (202) CFC # Urban Forestry and Human Benefits: College of Forest Resources, University of Washington 8