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GROTON — The phenomenon of leaves changing colors happens every autumn throughout the northeast, and driving through town, one can’t help but to notice the trees are approaching their glorious peak.

The timing of the autumn colors and leaf drop is being documented by Groton students who are participating in an ecological study that addresses an important current environmental issue, climate change.

GDRHS students currently in AP environmental science, taught by Melanie McCracken, are participating in a research project for the Harvard Forest LTER (Long Term Ecological Research) Schoolyard Program: Ecology Buds, Leaves and Global Warming. Students are looking at fall foliage to help scientists determine whether climate change brought on by the accumulation of greenhouse gases may affect trees.

“My philosophy about environmental science is that students love what they know, they know what they learn…going outside and learning in an authentic outdoor classroom is essential to understanding the environment,” said McCracken.

McCracken, having done her own study of leaves with past classes, was inspired by taking a Harvard forest workshop offered to teachers this past summer and decided that her class, for the first time, would participate in the Harvard Forest study.

Students are collecting data to answer these questions — how long is the growing season in our schoolyard? How might the length of the growing season relate to climate, and when does the growing season for trees in our schoolyard end this autumn?

At the edge of the high-school yard, next to the forest, tree branches with leaves are tagged for each student team. The class of 23, (seniors and three juniors) visits to collect data and make notations in their tree field ID guides until all study leaves have turned color or dropped.

On a recent chilly morning, the class headed outside to check for any changes. “The leaf drop determines something is different with the climate. We keep track of our branch each day to record how many leaves have fallen,” Gabrielle Johnson, a senior.

McCracken added: “To make good decisions concerning the environment in our everyday lives, students must understand their local environment first then apply that knowledge to local issues and then world issues.”

According to data that is being collected by Harvard Forest, Petersham, the leaves in Massachusetts are changing about three days later than they were two decades ago. Autumn’s’ colors are associated with cooling temperatures and decreased sunlight, which causes the production of chlorophyll to slow down as the leaves prepare to fall from the trees. The result is the leaves’ yellow, red and orange pigments, which are hidden for most of the year, are then exposed. The leaves fall off the tree when the tissue at the base of the stem no longer receives water and dries up.

Senior, Rick Liebold: “I’m observing how the temperature affects the color, leaf drop and whether global warming has an affect on the change.” His partner, Drew Daigle, a senior, added: We’re contributing to the study of global warming, its affects and reasons.”

The students’ data, posted on the Harvard Forest website, will be shared with scientists, other students and citizens who are interested in finding out how the length of the growing season is related to climate. The Harvard Forest website is http://harvardforest.fas.harvard.edu/museum/phenology.html.

“It’s easy to contribute to authentic scientific research. We can all be citizen scientists,” said McCracken.

It does makes one look at the autumn colors in a different light.