When Leaves Leave: Autumn reveals trees’ true colors!
By Kathy Reshetiloff
When Leaves Leave: Autumn reveals trees’ true colors!
Autumn always seems to sneak up. Slowly, the heat and humidity of summer is replaced with cooler, drier days. Here and there, autumn colors peek out of the green landscape. Then, before you know it, nature’s festival of color is in full swing. And just as quickly, it seems, the brilliant fall hues are replaced by dismal browns, and leaves carpet our lawns and gardens.
Actually, this leaf shedding process, known as abscission, begins before the colors appear. As summer’s heat fades, the cells where the leaf stem is attached to the tree toughen and begin to form a protective waterproof scar. The cells in the leaf stem swell, weaken and degenerate. This interferes with the flow of moisture and nutrients into the leaf, reducing the production of chlorophyll, which gives leaves their green color.
The leaf is the food factory for the tree. Chlorophyll in a leaf uses the sun’s energy to convert carbon dioxide and water into sugar, which is food for the tree. As the days shorten, there is less sunlight to manufacture food. Nutrients and minerals are withdrawn from leaves and transported to the permanent parts of trees, such as the trunk, stems and roots. Chlorophyll breaks down.
But leaves contain other pigments that give them their fiery fall colors. These colors are hidden in the spring and summer by the abundance of chlorophyll. Leaves reveal their autumn colors as chlorophyll breaks down and other pigments are unmasked.
The pigment called xanthophyll gives leaves a yellow color, and carotene produces yellow-orange. Leaves continue to produce sugar during the day, but colder night temperatures prevent trees from withdrawing the food from the leaves. Sunny days and cool nights can produce anthocyanin, a sugar-related pigment that turns leaves fiery red. Other chemicals and breakdown products give us bronze, purple and crimson hues.
The leaves of birches, beeches and tulip poplars turn golden. Sassafras leaves take on an orange tone. One of the more colorful trees, the sugar maple, may assume a yellow, orange, or red color — or any combination of these hues. The biochemistry that determines which of those colors it will be is not well understood, except that anthocyanin is abundant in red leaves and colder weather plays a role.
The red maple and staghorn sumac are two of the more vibrant red trees. Vines such as Virginia creeper and poison ivy also turn crimson. Oaks turn yellow, orange or bronze, or blends thereof. Leaves stay on oaks the longest and it is often their dry leaves that you hear rustling in the breeze. Some oak species, as well as beeches and hornbeams, hold on to all or some of their dead leaves throughout winter, in a phenomenon known as marcescence. There is no widely accepted theory as to why this happens, though some suggest it may be the tree’s way of capturing moisture by trapping snow or a strategy of waiting until spring to “fertilize” the ground below with decomposing leaves.
The final step of the abscission process is when a tree sheds its leaves. Gradually, the bond between the leaf and the branch weakens. The tiny veins that carried sap to the leaves all summer are sealed off. Wind and gravity finish the job, sending the leaves to the ground, where decomposition begins in earnest and turns them various shades of brown.
Dry, brown decaying leaves may not be beautiful, but they are valuable. Instead of bagging leaves, consider composting them and using the compost to enrich your garden soil. It’s an ecological and economical way to dispose of them and generally less labor intensive than raking and bagging.
Or you can simply mow the leaf-covered grass with a mulching mower, which chops the leaves into smaller pieces that decompose faster. Mulched leaves can be left on lawns to enhance the soil.
You can also spread whole leaves around vegetable gardens and flowerbeds or at the bases of bushes and trees. These leaves will form an insulating barrier around plants, reducing moisture loss and damage from severe winter weather. By putting whole and composted leaves on gardens and leaving mulched leaves on lawns, you reduce the need to fertilize. This cuts down on the amount of nutrients that run off the land into streams, rivers and, ultimately, the Chesapeake Bay.
Of course, leaves are good for other things too. Nothing beats jumping into a big pile of them on a crisp autumn day!
For information on leaf management and backyard composting, contact your state or local cooperative extension service.
About the Author: Kathryn Reshetiloff, a Bay Journal columnist, is with the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office in Annapolis.
Leaf Peeping in the Bay Watershed
Patapsco Valley State Park extends along 32 miles of the Patapsco River, encompassing 16,043 acres and eight developed recreational areas. Along with leaf peeping, there are lots of opportunities to hike, fish, camp, canoe, ride horseback, and mountain bike.
Terrapin Nature Park is the perfect spot for bird and leaf lovers alike. This 276-acre Queen Anne’s County Park is located on Kent Island and is the top eBird hotspot in Queen Anne’s County in terms of number of species reported. The park has a diversity of habitats that make it the perfect stop for a variety of birds during their fall migration.
This 184.5-mile trail is the fall foliage- and bike-lovers dream. The trail starts in Washington, D.C. and winds its way along the “Grand Old Ditch” to Cumberland, Maryland. There are a variety of spots to park and join the trail in both Maryland and D.C.
This popular destination is easily a fan favorite for many across the Chesapeake Bay region for its accessibility for drivers and hikers alike during fall. But don’t get caught up in the lines to the top of Old Rag, try out some of the other less traveled trails, like Bear Church Rock or even pop over to George Washington National Forest after your drive up Skyline Drive! If you’re planning to drive, make sure you plan your trip to enter at Swift Run or Rockfish entrance stations to avoid the longer lines at Front Royal and Thornton Gap entrance stations. And remember, be sure to keep your eyes peeled for wildlife crossings!
In one of Northern Virginia’s best kept secrets, fall foliage is nothing short of breathtaking! This forest located less than an hour from D.C. and an hour and a half from Richmond features a long scenic loop drive and lots of cool trails along babbling streams. The park also features plenty of opportunities to picnic, camp, cycle, and more.
Hit the trails here around Halloween, and you’ll see some of the best fall colors in Central Virginia! This park system features rocks, rapids, meadows, and forests—a little bit of wilderness in the heart of Virginia’s capital city. With rock climbing, cycling and hiking trails, paddling, bird watching opportunities, and more, this is the perfect spot to relax, unwind, and check out some foliage. Our Virginia Media Coordinator Kenny Fletcher highly recommends the Buttermilk Trail or Pony Pasture area for those looking for changing leaves.
Compliments of the Chesapeake Bay Foundation. Cbf.org