If you are like most people, autumn means one thing: the dreaded chore of raking leaves. In the Chesapeake region, autumn seems to sneak up on us. Finally, the heat and humidity of summer are gone, replaced by drier days and cooler nights. Here and there, glimpses of autumn colors peek out between green landscapes. Suddenly, it seems, just as one is beginning to notice the changes, those warm hues are replaced by dry brown leaves carpeting our lawns and gardens.
Actually, this leaf-shedding process, known as abscission, has been occurring for several weeks. Cells, located at the spot where the leaf stem is attached to the tree, toughen and begin to form a protective waterproof scar. The cells in the leaf stem itself swell, weaken and degenerate. This interferes with the flow of moisture and nutrients into the leaf, reducing the production of a pigment, known as 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, food for the tree. As the days shorten, there is less sunlight energy 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 Nutrients and minerals are withdrawn from leaves and transported to the permanent parts of trees such as the trunk, stems, and roots.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, though, are hidden most of the year by the abundance of chlorophyll, making leaves appear green.
Leaves reveal their autumn colors as chlorophyll breaks down and other pigments are unmasked. Xanthophyll produces the color yellow, and carotene, like that in carrots, produces yellow-orange. Leaves continue to produce sugar during the day but cold night temperatures prevent trees from withdrawing the food out of the leaves. Sunny days and cool nights can produce a sugar-related pigment, anthocyanin, which produces fiery reds.
Other chemicals and breakdown products produce bronze, purple and crimson.
Birches, beeches and tulip poplars turn golden. Sassafras trees 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 red maple and staghorn sumac are two of the more vibrant red trees. Vines such as Virginia creeper and poison ivy also turn crimson. The oaks turn a variation of yellow, orange or bronze. Leaves stay on oaks the longest and it is often their dry leaves that you hear rustling in the breeze.
The final step in the abscission process occurs when a tree sheds its leaves. Gradually, the bond between leaves and a tree weakens. The tiny veins that carried sap to the leaves all summer long are sealed off. Leaves then fall to the ground encouraged by wind or by the sheer weight of gravity. Now the dominant color is brown as the chemical reaction of decomposition starts. Although the dry, brown, decaying leaves may not be beautiful, they are extremely valuable.
Most of us spend hours raking leaves, and putting them into plastic garbage bags, only to have these bags buried in a local landfill, taking up ever-decreasing and valuable space. The most ecological, economical and least labor intensive way to "dispose" of leaves is to compost them.
As the leaves decompose, they release nutrients back into the soil. If you have a mulching mower, leaves can be cut into smaller, faster-decomposing pieces. Mulched leaves can be left on lawns and will actually enhance the soil, reducing the need to fertilize the yard next spring. Leaves can also be raked into a pile and shredded with a regular lawn mower.
Spread whole leaves around vegetable gardens, flower beds, bushes and trees. The decomposing leaves will contribute nutrients to these areas as well. The leaves also form an insulating barrier around plants, reducing moisture loss and damage from severe winter weather.
Composting leaves saves time and money. Soil covered by composted mulch is less likely to erode. Applying compost to yards and gardens reduces the need to fertilize. This cuts down on the amount of nutrients that run off the land into streams and rivers and, ultimately, the Bay. Of course, leaves are good for other things too. Nothing beats jumping into a big pile of leaves on a crisp autumn day!
Note: Another autumn phenomenon is the annual migration of birds tosouthern wintering grounds. National Wildlife Refuge Week, October 12-18, 1997, is timed to coincide with this annual migration when millions of birds will fly into the lower 48 states. National Wildlife Refuges provide some of the best opportunities to observe and photograph waterfowl and other wildlife. In Delaware, visit Bombay Hook NWR in Smyrna; in Maryland, stop by Patuxent Wildlife Research Center in Laurel, Blackwater NWR in Cambridge or Eastern Neck NWR in Rock Hall; and in Virginia, visit Back Bay NWR in Virginia Beach; Chincoteague NWR in Chincoteague; Eastern Shore of Virginia NWR in Cape Charles; Mason Neck NWR in Woodbridge or Presquile NWR in Hopewell. For additional information on National Wildlife Refuge Week, call 1-800-344-WILD.