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Protect our urban forests

Environmentally Speaking

Posted: March 20, 2008 12:55 a.m.
Updated: May 21, 2008 5:03 a.m.
Santa Clarita has an oak on its city seal and has long been a "Tree City, USA," holding annual arbor day events to promote local tree planting. This year's Arbor Day celebration will be held on April 12, and we hope to see you there again at our Friends of the Santa Clara River booth. It is wonderful that the city promotes this event and acknowledges the importance of urban forests. Now the city needs to be more proactive about protecting our native trees during the land-use process.

Forests and trees in urban areas provide many benefits, among which is improved health for city residents. This fact should inspire citizens of Santa Clarita to take a close look at development projects that reduce tree cover including projects that impact riparian zones along the Santa Clara River.

Native oaks, sycamores and cherries are especially important because they tolerate our drought cycles and use less water than non-natives such as eucalyptus. We were disappointed to see the city approve the Gates-King industrial project in the Newhall Pass, which will remove 1,400 oaks from an area plagued by air pollution at the same time that this project will add 27,000 trips per day to the Newhall Pass.

Then, two weeks ago, the city supported a 472-unit project that will remove 72 oaks in Tick Canyon. It takes hundreds of years to replace such native forests, if they can be replaced at all.

The Trust for Public Land has analyzed urban forest benefits in its report "The Economic Benefits of Land Conservation." The discussion that follows is based on the Trust for Public Land study.

Reduced air temperatures are one important benefit of urban tree cover. Trees lower air temperature by providing shade, of course, but also through transpiration cooling (evaporation of moisture from leaves). Reduced temperatures lead not only to increased human comfort, but to reduced pollution levels and less summertime energy use by urban buildings, which in turn, leads to a reduction in pollutant emissions from power plants.

The economic value of the temperature effect has not been quantified; however, the EPA has estimated the cost of reducing ozone levels by one part per billion through nitrogen oxides limitations by electrical utilities could exceed a half-billion dollars annually in the United States. It therefore can safely be concluded that any temperature reduction effects leading to reduced pollutant formation or emissions will have large payoffs.

Trees also remove pollutants directly from the air through a process termed "leaf stomata." Removal rates are on the order of 11 grams per square centimeter of canopy cover per year of such pollutants as ozone, sulfur and nitrogen dioxide as well as particulate matter under 10 microns in size - the most harmful to human health. The economic value of this effect is estimated at $663 per year per hectare (about 2.5 acres) of canopy in the city of Atlanta, Ga.

Tree cover around buildings serves to conserve energy in summertime through both shading and lower temperatures. This effect is less predictable in winter and could be reversed. The economic benefit due to altered building energy use from tree cover is estimated at $2.7 million per year in Washington D.C.

Increased tree cover also leads to reduced runoff though processes of rainfall interception, evapotranspiration and increased soil infiltration. This effect also delays peak flows during large storm events and thus can lower the size and cost of storm water treatment facilities. The economic benefit of this effect has not been quantified but is expected to be significant.

Urban tree cover can improve water quality in our rivers and aquifers by reducing runoff and air pollution, and by filtering, assimilating, absorbing, or degrading many chemical pollutants in water flowing through forested areas, including sediments, pesticides and metals.

The economic value of this effect is very large. Damage to streams, lakes and estuaries from nonpoint (general runoff) sources was estimated at $7 to $9 billion per year in the United States in 1986 and is likely double that at this point in time.

In summary, forests and trees in urban areas provide many environmental and economic benefits that can lead to improved human quality of life. As discussed above, these benefits include improved air and water quality as well as reduced air temperatures, reduced pollutants and energy conservation. We urge the city to not only "talk the talk" at its wonderful Arbor Day celebration event, but also "walk the walk" with its land-use planning decisions.

Ron Bottorff is chairman of the Friends of the Santa Clara River. His column reflects his own views, not necessarily those of The Signal.


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