The National Arbor Day Foundation has recognized Cambridge, Massachusetts, award this year with the Growth Award and Tree City U.S.A for the health of trees with in city limits. Cantabrigians say there are more trees in Cambridge than any other city in the country. Cambridge does seem like a forest in some ways; trees line the sidewalks, dot parks, fill tiny private yards. My biology class set out today to measure the biodiversity of our urban forest; the types of trees were planted, how old and how healthy they were. I'm sure our methods were way less precise than those of the National Arbor Day Foundation, since we were only able to study the trees on one block. We used a transect, a traditional tool of scientists exploring biodiversity. Usually a transect is taken in a rainforest or some other cool place but you take what you can get. Basically the enterprising scientist picks their section of forest (Sumner Road, near Harvard square), measures out a rectangle, and records all the species he or she finds there. With trees, a scientist must also measure the circumference, which can tell the tree's age. In our 1 block length x street width rectangle we found 13 different trees of 6 different species, varying in age from 5 - 80 years. This is only counting sidewalk trees, not the ones in private yards. All of you in the 'burbs or the country may not be impressed but keep in mind we're talking about a CITY.
Of course, in a real forest could be hundreds of types or trees in an area that size. It is always important to have different types and ages of trees in an urban or otherwise ecosystem. Forests work better with many types of trees than with one. A forest with only a few types of trees means individual trees compete more for water and nutrients, support fewer other plants and animals, and are more susceptible to decease. In the early 1900's, cities planted hundreds of thousands of America's favorite tree, the great American chestnut. The trees were a monoculture; they were all of the same type, and all right next to each other. In 1904 imported Japanese chestnuts brought with them a fungus American chestnuts couldn't withstand. The fungus swept though cities, spreading easily from one chestnut to another one planted just down the block. Eventually, it spread to forests as well. By 1950 there were no American chestnuts left, although researchers for the American chestnut Restoration Project are working to create a disease resistant hybrid from Japanese chestnuts and American chestnut seed.
While I was glad to see Cambridge had a healthy and diverse crop of trees, I couldn't help but wonder why Cambridge has so many. Trees are expensive; they have to be planted, watered, pruned, mulched, all of which costs money. Trees can also be dangerous, they can't be placed near power lines, they can damage property in storms. After hurricane Katrina, many property owners in New Orleans cut down trees in their yards, believing they weren't worth the risk. Most communities regard trees as luxuries, contributing to the character of the neighborhood, but not an absolute necessity. In the town of Ware, Massachusetts, they even cut down all the trees along main street and put plastic trees on the stumps. Trees in Cambridge are probably part of the look; all the trees that I saw were some type of maple, whose red Fall colors give Cambridge that Old New England, Ivy-league feel that has impressed and intimidated tourists since 1636. However, trees in cities have real economic benefits. They help regulate temperature, keeping cities cooler in the summer and warmer in the winter. They improve the air quality. They limit the effect of floods by absorbing and holding water in their roots. The damage from floods and poor air quality, and increased heating and cooling costs would cost money.
Trees also have an elusive and hard to measure effect on how people feel. On average, people in cities with less trees claim to feel more stressed out. A hospital patient will recover faster when placed in a room with a view of a tree through a window. Trees make people feel, comfortable, relaxed, safe. As a city, Cambridge has it's ups and downs; living here is expensive, and while Cambridge wasn't hit very hard by the 2008 recession, many people are jobless, homeless, or struggling to pay their bills. However, I think the good outweighs the bad; Cambridge is clean, crime is low, and support all the little shops and businesses and the city is full of college students that make living here fun. Most people don't think about our trees as being part of Cambridge prosperity, but trees have been under appreciated for hundreds of years. What unmeasured effects do a healthy, diverse forests have on our wallets and our quality of life?
No comments:
Post a Comment