What makes Autumn Leaves Turn Crispy Red?
Red maple leaf in the fall
The air is crisp. Apple crisp is baking in the oven. Leaves will soon be crispy underfoot in the deciduous forest. For now, the color show marching southward from Acadia National Park along the Appalachian chain, through Shenandoah National Park and on into the Smokies offers us an effective diversion from thinking about the impending crisp winter weather to come.
Some years here in New England, the show is simply acceptable, and others, absolutely spectacular. Those trees that turn yellow seem to do so fairly regularly with not much of a yearly alteration. Red trees on the other hand, seem to make all the difference. What causes trees to turn red at this time of year?
Without getting too technical it is fairly straightforward to explain. For those who like technical, the pigment compounds are termed as follows: anthocyanin for red and purple plant pigmenst; carotenes and xanthophylls for those pigments that are orange and yellow respectively; and chlorophyll for green pigment.
At this time of year green plant pigment is dying off faster than it is begin replaced. Heartier yellow and orange leaf pigments that were masked by the green are now being revealed. The effect is stunning on birch, hickory, maple, witch hazel, willow and many other trees that typically display yellow.
Red pigment, on the other hand, is produced at this time of year. Sugar maple, red maple, sumac, burning bush, red-osier dogwood, red oaks, pin oaks and others typically showcase red. The brightness and amount is dependent upon various environmental factors that change from year to year and one location to another.
As deciduous leaves stop photosynthesis in the fall in response to changing day length, sugars begin to accumulate. These sugars combine with a compound to make this red pigment. Several conditions, when combined together at this time of year can serve to make that pigment bright and showy.
*Acid sap: If the tree is located in acidic soil making its sap on the acid side, bright red leaves result. Alkaline sap tends to mute the pigment into more of a purple color.
*Dry weather: Lack of water getting through to the leaves tends to make the red even redder. Rainy falls find trees still turning red, but not quite as bright.
*Light: Our days are getting shorter at this time of year here in the northern hemisphere, but the earth is getting closer to the sun. Bright sunny days will produce bright red moreso than overcast days.
*Low temperatures: Nighttime temperatures that hover just above freezing kill off that chlorophyll at a faster rate and enhance the formation of the red pigment.
So keep an eye on the weather and the autumn colors and see what correlations you can make.