Autumn Colors

September and October in Vermont bring reminders that chemistry (and biochemistry) have some dramatic consequences for the visual landscape. As temperatures drop, the trees decide that it's best to shutdown the chlorophyll factory for the year. Chlorophyll contains those wonders of natural synthesis, metallo-porphyrins, which are the heart of the photosynthetic engines that capture atmospheric CO2 and produce organic matter in copious quantities. But chlorophyll only survives for a short time in the leaf of the tree -- sunlight drives photosynthesis, but causes it to be decomposed after weeks and months. So the trees must constantly remake it through the summer. In late September, chlorophyll production ends and the other components of the leave dominate: anthocyanins (good absorbers in the blue, reflectors in the red) and beta-carotene (yellow reflectance) remain in the drying leaf. The roles of these latter two are not fully understood in the processes of the leaf, but at least in part, anthocyanins absorb the bluer parts of the sunlight to reduce the amount of photolysis of the chlorophyll -- they are protectors. (Ref.: American Scientist vol. 90 p. 524, 2002, Why Leaves Turn Red.)

Here are some examples from the Northeast Kingdom.

Leaf color in Danville. Maples, birches, beech, ash, hemlock, and more.

Late afternoon in Steam Mill Brook
 Wildlife Management Area, Vermont

Danville in late September