Fallcoming

I realized one day too late that yesterday was the Fall Equinox. Although the nights have been getting cold and sweater weather is approaching, the green leaves around the Mountain House have fooled me into a false sense of summer. The endless shorts weather and long naps in the sun are coming to a close, but that means it is almost time for fall foliage--something I'd never really seen before coming to Hamilton. We've all seen the leaves on campus turn red, gold, or yellow in the fall, and the brilliance and variety of leaf color up here bring flocks of people to the Park. Although leaves change color all over the world, places like the Adirondack and Smoky Mountains are known for their especially dramatic colors because of the especially dramatic temperature differences between night and day in fall months. Already, at higher elevations where the temperatures are lower, fall is becoming very apparent. Since peak foliage is so short and will probably be at the Mountain House in a week or two, I wanted to read more about what is happening.

When nights get cold but are not yet below freezing, deciduous trees prepare to shed their broad leaves by closing off the circulation paths that exchange water and sugar. In the day, these leaves are still producing lots of sugar in the hot sun, but these sugars build up within the leaf. When leaves turn red or purple, it is because the excess sugar in the leaf produces a red chemical classified as an anthrocyanin (what makes cranberries red). Yellow leaves, on the other hand, turn yellow because the chlorophyll is no longer being produced in the leaf, eliminating the green pigment and allowing the yellow chemicals (carotenoids) that were already present in the leaf to be displayed. Whether a leaf turns red or yellow is mostly dependent on the type of tree: Oaks tend to turn red, birches tend to turn yellow, and maples differ depending on the specific species. 

Kianee posted a couple of weeks ago about the idea of fall foliage as "teaching us how to die", an idea inspired by Thoreau. I think that this is a beautiful image, and even more so because fall foliage is not just a spectacular example of death in the natural world, but a way that the death and decay of leaves actually helps that same tree--and all of the organisms surrounding it--revitalize itself in the spring. The variety and complexity of the seasons up here is one of my favorite things about the Adirondacks, and we are right now on the cusp of entering the second one of the semester.

Source:

USDA Forest Service, "Why Leaves Change Color". http://www.na.fs.fed.us/fhp/pubs/leaves/leaves.shtm