As we garden, we stoop over to weed, to trim dead branches or to deadhead. With our 5-foot or 6-foot frames, we look down at the tops of our flowers and bushes. We make all the assessments about our gardens from this vantage point.
What if we changed that perspective a bit and looked down at our gardens from a low-flying airplane or hang glider? What telltale piece of information we could glean about our garden from that height?
A forest’s canopy is the area above the forest floor where tree crowns meet to form a habitat for both plant and animal populations. Of the 30 million types of organisms, many live in the forest’s topmost portion. The canopy provides photosynthesis, creating carbohydrates that in turn fuel the ecosystem. The canopy also acts as a buffer between the soil and the atmosphere, protecting the soil from erosion as well as removing pollutants from the air and rain.
A single old-growth Douglas fir provides over 4,000 square meters, almost an acre, of foliage surface capable of capturing particulate matter from the atmosphere, which then can be decomposed and become a supplemental nutrient source.
In 1986 the National Urban Forest Council analyzed the trees on streets in twenty cities. They found that for every tree planted, four were being lost. The research was expanded in 1989 to 413 cities in 30 states. (See “The State of the Urban Forest,” J. James Kielbaso and Vincent Cotrone, American Forests, October 1989, pp. 11-18.) The study showed further decline, including that the average life of a downtown street tree was only thirteen years.
In 2007 the American Forests organization analyzed the urban ecosystem of Bellevue, a city fairly close to our valley. The American Forests’ goal for a tree canopy for a city is 40 percent, and Bellevue was close to that goal with 36 percent. The sad news, however, was that it had lost 21 percent of its tree canopy since the 1998 analysis. What did that mean in terms of both the ecosystem and a dollar amount?
Bellevue vegetative land cover lost its ability to remove about 30,000 pounds of air pollutants a year, a process valued at $68,000. Without the canopy to reduce storm water runoff volume, the city had to manage an additional 755,000 cubic feet of storm water, a task valued at $1.5 million (“Urban Ecosystem Analysis City of Bellevue, Washington,” 2007, americanforests.org).
We can look even closer … at Puget Sound. “Areas with high vegetation and tree canopy coverage (those with 50 percent tree cover or more) have declined by 37 percent” (“Regional Ecosystem Analysis Puget Sound Metropolitan Area,” 1998, americanforests.org). The study reports that lost tree canopy could have removed about 35 million pounds of pollutants annually.
On a worldwide basis, it’s estimated that every minute over 100 acres of tropical forests get deforested. The World Resources Institute estimates that only about 22 percent of the world’s (old growth) original forest cover remains intact — most in Canadian and Alaskan boreal forest, the boreal forest of Russia, and the tropical forest of the northwestern Amazon Basin.
The organization American Forests recommends an average of 40 percent tree canopy for cities in the Pacific Northwest. One benefit is that if cities maintain enough tree cover, they can reduce the need for infrastructure to manage air and water resources. It would be interesting if our city councils would seriously consider planting trees not only as landscaping to beautify a street’s divider or a bare corner, but also as a goal to improve the health of our ecosystem.
We can make a quick assessment to see if we have room in our landscape for more trees.
If each one of us planted even one more tree, think how that would affect the tree canopy of our valley.
We’ve had such a miserable winter that it would be fun now to visit one of our local nurseries after we’ve evaluated our property and figured out how many more trees we might plant. To help you decide among several trees, go to www.greatplantpicks.org and click on “small trees.” A benefit of this website is that the selections are picked by professionals and the choices are known to do well in our climate. All of the trees are described and most shown in photos.
For evergreens, consider the pyramid-shaped Abies koreana (Korean fir) or the slow-growing conical Chamaecyparis obtusa ‘Gracilis’ (Dwarf hinoki cypress).
Possibilities for specimen trees are Acer tegmentosum ‘Joe Witt’ (Manchurian snakebark maple), with its distinct tiger-striped bark; Chionanthus retusus (Chinese fringe tree), with panicles of fragrant white flowers in summer; Oxydendrum arboretum (Sourwood), with vivid shades of red, purple, and yellow in autumn; Stewartia monadelpha (Orangebark stewartia), with red brown bark and pink-red foliage in autumn or Styrax obassia (Fragrant snowbell), with flowers on 6” racemes in late spring.
In the Pacific Northwest, our trees are sacred to us. As Easter, a time of resurrection, approaches, we can participate in that spirit by planting a tree or two, increasing our valley’s life-sustaining tree canopy.
Beverly Hoffman’s Sequim Gazette column appears the third Wednesday of each month. She can be reached via e-mail at firstname.lastname@example.org.
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