Wednesday, July 14, 2010

PROJECT PROFILE: Red Oak vs. Tree of Heaven

By Leah Nagel

My project this summer is looking at the urban-to-rural gradient between downtown Boston and Harvard Forest. This research is a small piece of a larger project that is looking at the differences in a variety of factors along the gradient. These factors can include changes in the concentration of atmospheric CO2, nitrogen levels in the soil and in tree leaves, and pollution. My personal project is looking at how changes in all of these factors between the two endpoints of the gradient impact the growth rates of two trees: red oak (a tree that is native to Massachusetts) and the tree of heaven (an invasive that was brought over from China over 200 years ago).

Red oaks are fairly common throughout Massachusetts, so finding trees in the Forest and in the Arnold Arboretum in Boston was not particularly difficult. However, while the tree of heaven can be found almost anywhere in Boston, for a highly problematic invasive species, it has been quite difficult to locate anywhere near the Forest. I finally found one large tree and a few saplings in a nearby town. Since locating all of the trees I needed for my research, I have been spending most of my time coring those trees and measuring their growth rings to get a sense of how fast these trees grow. The remainder of that time has been spent learning how to use the program, R, to analyze my data and to convert giant tables of ring width and climate data into friendly graphs.

Eventually, I hope to be able to do several things with these data. First, I want to compare growth rates between species growing in the same location to see how they behave under similar conditions. Next, I want to look at differences within each species when they are grown in urban versus rural environments. Then, I can compare those differences between species (particularly considering that red oak is a native species and tree of heaven is an invasive). I also plan to look at how growth rates impact carbon sequestration: the faster trees produce new wood, the faster they sequester carbon, but the amount of carbon sequestered in each ring that I measure depends on a lot of variables, including the species of tree and the age/size of that tree. All in all, I hope to do make many manipulations with the data I am collecting, and hopefully by the end of the summer, I will have an interesting story to tell about what’s going on with trees growing in very different places in Massachusetts.

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