So you have all probably heard me wax philosophical about the beauty of the fall foliage out here in the East where the leaves change (as I do here, describing one of the first hikes I went on after I came East). If not, you probably haven't been reading my blog enough :) More importantly, you should know it is one of the most spectacular natural phenomena anywhere in the world. Nature's optical symphony, if you will.
Walking in these wonderous vistas has often prompted Aviva and I to discuss why the leaves change, but we never seem to come upon a satisfactory answer. Of course, it is easy to look something like this up on the Internet, ... just not when you are out in the woods enjoying it. So yesterday, after we returned from our quick jaunt through the Arthur E. Butler Memorial Sanctuary in eastern Westchester, I spent some time researching this foliage phenomenon.
Aas summer moves into autumn, and the amount of sunlight gets less and less, eventually it gets to be too little for the trees to use for photosynthesis to produce the glucose they need for food. So the trees produce less and less chlorophyll as the sunlight gets less and less, reducing the green color we see in the leaves over the summer. The green color actually covers up some of the other colors present in the leaves, specifically the yellow/gold colors, which are produced by carotenoids (you know, the chemicals that make carrots orange and that we like to have a lot of as beta-carotene) and are present year round but are covered up by the chlorophyll in the summer. When the green of chlorophyll leaves (ha ha) during the winter, the gold, yellow and orange colors from the carotenoids shows up, no longer obscured by the brighter, green cholorphyll.
Reds are a different matter, as they are the result of a different set of chemicals called anthocyanins, which are not present in all trees. Anthocyanins are generated in response to weather, particularly when temperatures are warm during the day, but cool at night. When this occurs, the glucose produced by leaves in the sunlight is trapped in the leaves by the cooler temperatures at night, which solidify the glucose and prevent in from flowing back into the branches and trunk where it can be stores. Anthocyanins are chemicals that are produced to protect the leaves from the lose of nutrients due to colder temperatures, as they allow a plant to recover the nutrients in its leaves before they fall off.
Overall, it is a lot more complicated than that, but that's the basics. I find it really fascinating that the different colors are linked to different processes, because that knowledge means that seeing the leaves change is like seeing the molecular processes of the trees in action. Dorky I know, but hey, I am a biologist. Its probably a good thing that this stuff fascinates me ... and whatever you think of the process, the results certainly make fall a treat for those of us out here in the Northeast.
These pictures were taken while I was hiking at Teatown Lakes (first two) near Ossining, Arthur E. Butler Memorial Sanctuary (third) and in Slide Mountain Wilderness area.