Falling for a Blue Ridge Autumn

The lure of the Blue Ridge Parkway is color.  During the spring and summer, the lush mountain coves are sprinkled with the colors of flame azalea and Catawba rhododendron, along with many other wildflowers, mushrooms, animals, and trees.  In fact, the mountains themselves take on a hazy blue appearance.  Eventually, shorter days and cooler temperatures cause the blanket of blue haze to lift so that the trees can show their true colors.

The spectacular display of color that usually occurs in October is the result of an elaborate process in which the tree shuts down the green chlorophyll that captures solar energy.  Chlorophyll is abundant during the spring and summer, when the tree produces sugars through photosynthesis.  As the summer comes to a close, the chlorophyll breaks down within each leaf and the yellow xanthophylls and orange carotenoids that were present all along begin to show.  In some species, anthocyanins, which allow for the red coloration, are produced.  As the xanthophylls and carotenoids break down, the vibrant red appear, giving trees such as maples a transition from green to yellow to red.

While the color change occurs, the tree builds a layer of weak cells known as the abscission layer.  This abscission layer seals off the living tree from the leaf.

With winter just around the corner, the colors will fade to a muted brown as the last of the moisture is released and the wind rustles the leaves falling to the ground.  The temperate deciduous forest of the Appalachian Mountains complete this annual cycle of color change in order to survive.  During the winter, very little water is available in the frozen ground and a broad-leaved tree would be unable to replenish water lost through the leaves.  Leaves add thousands of square feet of surface area to mature trees.  If these leaves were not shed, snow and ice would accumulate rapidly and weigh the tree down causing the limbs to break or the tree to fall.

Leaf litter on the forest floor builds up year after year.  As the leaves pile up and slowly break down, they hold in moisture and add organic matter to old Appalachian soils.   The white winter layers the grounds with snow and ice and the trees are also adorned with icicles and cloud moisture frozen on the branches.  In the spring, the snow melt seeps into the ground and the leaf litter will give way once more to the lush greenery and colorful wildflowers as the season kaleidoscope of color begins again.
       

James Parker, former seasonal Education Ranger, Peaks of Otter