By E. Gregory McPherson and James R. Simpson
Davis, CA (January 1, 1999)- The Pacific Southwest Research Station’s Western Center for Urban Forest Research and Education has developed a tool for utilities, urban foresters and arborists, municipalities, consultants, nonprofit organizations, and others to use to determine the effects of urban forests on atmospheric carbon dioxide (CO2) reduction. A general look at these guidelines provides an overview the benefits of urban tree planting and the most effective ways to plant in order to reach these benefits. This guide provides specific information on how to design a tree-planting event, the ideal locations for planting trees, as well as selecting the ideal tree types for CO2 reduction.
Urban Forests and Climate Change
Gases that make up the Earth’s atmosphere trap the sun’s heat, creating a natural “greenhouse effect” that makes our life on the earth possible. Recent human activity has led to an accumulation of greenhouse gases (GHGs) in the atmosphere. Carbon dioxide (CO2) is one of the most important GHGs produced by people. Carbon dioxide is emitted when we burn fossil fuels to produce energy and heat, and to power vehicles.
Urban forests can store CO2 as trees grow. As long as trees are actively growing, they reduce CO2 in the atmosphere. Trees around buildings can reduce the demand for heating and air conditioning, thereby reducing emissions associated with production of electric power. An urban forest can become an important storage site for CO2 through tree planting and stewardship that increases canopy cover, as well as through strategic planting that cools urban heat islands and saves energy used for space heating and air conditioning. Although urban forestry-based CO2 offset projects may not be as cost-effective as rural forestry projects, they can provide many social, economic, environmental, political, and public relations benefits to utilities and city residents.
Shade Tree Programs
Frequently, shade tree programs are partnerships between utilities, non-profits, and local municipalities. Such programs offer opportunities for building better communities through investment in urban and community forestry. Tree planting and stewardship activities involve issues such as conservation education, neighborhood revitalization, job training, improving air and water quality, conserving energy and water, and recycling green waste. Forest Service research suggests that when the economic value of benefits trees produce, such as removal of air pollutants, are assessed, total benefits can be two to three times greater than costs for tree planting and care (McPherson 1995).
Where to Plant Trees:
* The west and northwest sides of a home are the most important sides to shade.
* Locate trees to shade windows so that they block incoming solar radiation, but do not block views.
* Trees located to shade south walls can block winter sunshine and increase heating costs.
* If the roots of trees are too close, they can damage the foundation.
* Shading your air conditioner can reduce its energy use, but do not plant vegetation so close that it will obstruct the flow of air around the unit.
* Locate trees in common areas, along streets, in parking lots, and commercial areas to maximize shade on paving and parked vehicles.
* Contact your local utility company before planting to locate underground water, sewer, gas, and telecommunication lines.
* Note the location of power lines, streetlights, and traffic signs, and select tree species that will not conflict with these aspects of the city’s infrastructure.
* Avoid locating trees where they will block illumination from streetlights or views of street.
* The ideal shade tree has a fairly dense, round crown with limbs broad enough to partially shade the roof.
* A large tree will provide more building shade than a small tree.
* Match the tree’s water requirements with those of surrounding plants.
* Conifers are preferred over deciduous trees for windbreaks because they provide better wind protection.
* Norway spruce (Picea abies), white pine (Pinus strobus), Scotch pine (Pinus sylvestris), white fir (Abies concolor), American arborvitae (Thuja occidentalis), and Douglas fir (Pseudotsuga menziesii) are among the best windbreak trees.
* Inspect your tree at the nursery or garden center before buying it to make sure that it is healthy and well formed.
* Water the new tree twice a week for the first month and weekly thereafter for the next couple growing seasons. Inspect your tree several times a year, and contact a local landscape professional if problems develop.
* By keeping the tree healthy, you maximize its ability to reduce atmospheric CO2 and provide other benefits.
Carbon Dioxide Reduction Through Urban Forestry: Guidelines for Professional and Volunteer Tree Planters