Trees: A resource we can’t afford to waste
By Vicki Wolf

It is well that you should celebrate your Arbor Day thoughtfully, for within your lifetime the nation's need of trees will become serious. We of an older generation can get along with what we have, though with growing hardship; but in your full manhood and womanhood you will want what nature once so bountifully supplied and man so thoughtlessly destroyed; and because of that want you will reproach us, not for what we have used, but for what we have wasted.

-Theodore Roosevelt, 1907 Arbor Day Message

Americans have not heeded Theodore Roosevelt’s warning about the preservation of trees given almost a century ago. Trees have been disappearing at an alarming rate, especially in urban areas across the United States.

The American Forests Report Urban Ecosystem Analysis of Houston from 1972 to 1999 shows that in the Houston metropolitan area, forest areas have declined and developed areas have expanded. The report found a trend of declining heavy and medium tree canopy cover suggesting that as new development occurs tree canopy is not being conserved. www.americanforests.org/graytogreen/air/

Trees are the oldest living things on the planet, and they play an important role in the health of the environment. Trees provide natural, cost effective protection from forces of nature such as wind and stormwater management. They beautify, provide shade, reduce noise pollution, and make living and working environments more humane.

The role of trees in a healthy environment
Exposure to air pollutants, including ozone, toxins and particulate matter, is associated with respiratory disease, asthma, heart disease and other illnesses (see “Human Body Under Attack”, Health Section, ). Trees play a significant role in removing pollutants from the air.

Trees help remove carbon dioxide, one of the gases contributing to global warming, from the environment and convert it into oxygen during photosynthesis. One acre of trees provides enough oxygen for 18 people and absorbs as much carbon dioxide as a car produces in 26,000 miles.

Trees remove sulfur dioxide and nitrogen oxide – two major components of acid rain and ozone pollution – from the air as well as benzene, formaldehyde and many other toxic chemicals. Trees also are effective in removing particulate matter (2.5 microns or smaller) from the air.

The economic impact of the air cleansing provided by trees is significant. According to the American Forest Report, in 1999 the tree canopy in the Houston area removed 83 million pounds of pollutants, valued at $208 million, annually. Tree cover as it existed in 1972 would have removed 98.5 million pounds of pollutants at a value of $247 million. The dwindling Houston tree cover has an economic as well as environmental impact.

Natural wind, erosion and stormwater control
Trees can reduce wind speeds by up to 85 percent compared to treeless areas. The root systems of trees prevent erosion by holding soil in place. Trees and soil work together to reduce stormwater runoff: Trees intercept rainwater on leaves, branches and trunks. Some of the intercepted water evaporates into the atmosphere and some soaks into the ground. Peakflow of stormwater is reduced, which helps prevent flash flooding.

According to the USDA Forest Service, a city’s trees can reduce peak storm runoff by 10 to 20 percent. The Houston Ecosystem Analysis conducted by American Forests examined the total volume of stormwater storage avoided in Houston because of trees in 1999 and found that the existing tree canopy reduced the need for storm water management by 2.4 billion cubic feet saving about $1.33 billion in one-time construction costs.

Trees also help to purify the water. Tree roots filter ground water, trapping nutrients and pollutants and then draining them from Houston’s stormwater and bayou systems into the Gulf of Mexico. This natural process helps to protect the region’s fishing industry which is threatened by runoff that contains pesticides and highway pollutants. www.ghasp.org/publications/trees/trees.pdf

Shade and noise buffer in an urban heat island
Houston is one of the hottest cities in the nation. Trees help reduce the urban heat island by providing shade. Lands with heavy tree cover can be at least two to four degrees cooler during summer. The cooling effect of trees helps lower energy costs and reduces pollution. In 1999, Houston’s direct residential summer energy savings, as a result of tree shade, was estimated at $26 million annually, according to the American Forests Report.

Trees act as a buffer to absorb urban noise. A 100 foot wide and 45 foot tall patch of trees can reduce noise levels by 50 percent, according to the U.S. Department of Energy.

Trees enhance relaxation, well-being and community
The University of Illinois Human-Environment Research Laboratory studied how contact with trees influenced the lives of people living in Chicago’s Robert Taylor Homes, the largest public housing development in the world. The researchers found that people gathered in common spaces that contained trees significantly more often than they gathered in spaces that had no trees. They found that the urban forest provides a setting for neighbors to get to know one another. They build stronger relationships among themselves and develop a support system that provides alternatives to violence. Indeed, the study revealed that people who live near trees have significantly less violence in their homes than people who live in places without trees. www.lpb.org/programs/forest/casestudies.html

Theodore Roosevelt’s prediction in his 1907 Arbor Day Message has come to pass: today “the nation’s need of trees” has become serious. Buildings and parking lots take the place of more trees each year in urban heat islands. Air-conditioning indoors in front of computers and TV sets is more likely to be the summer pastime for children than sipping lemonade under a shade tree. How many Houston children today even know how to climb a tree?