First the beauty's all around, and then it's on the ground.
The sugar maples here are dropping their leaves. The ashes dropped their yellow leaves a week ago: the red and white oaks still hold on to most of their sturdy brown and scarlet leaves. Local folk wisdom says that the more the leaves hang on the oaks, the more snow we can expect in the coming winter.
Trees grow leaves in the spring from the carbohydrate reserves stored in their roots. Later in the growing season, more leaves, along with stems, flowers and fruits are produced from the fresh sugars made by the first leaves.
Once unfurled, leaves become elegant solar collectors. Using the energy in sunlight they combine water from the soil and carbon dioxide from the air to create sugar and oxygen. That sugar, called glucose, stores some of the sun's energy in the bonds between its six carbon atoms and provides the base of nearly every food chain. These sugars also provide the energy and most of the materials needed to make trees a little bigger each year, i.e., to create another growth ring around the entire tree - from the tip of the roots to the end of each branch.
All season long, leaves carry on the amazing process of photosynthesis. They capture energy from the solar flux which powers our planet and store that energy in wood, leaves, fruit, and sap. Green plants are the only real producers on Earth. Everything and everyone else consumes.
As they collect solar energy, leaves simultaneously release oxygen, reduce air pollution and cool the environment by transpiring water and absorbing some of the sun's energy. The sugars produced then flow to where they are needed. They combine with minerals from the soil to create new leaves, wood, flowers and fruit, or to fill storage cells in the roots, depending on the season. We may harvest some of this production by collecting the maples' sap for making syrup, gathering hickory nuts for nutritious food or cutting oak trees for lumber and firewood.
Now is the time of year these solar collectors stop working and drop off to reenter the continually cycling pool of nutrients in the soil which nourishes all life. Soon it will be too cold for trees to keep water flowing to their leaves. The sun sinks to a lower angle and has much less intensity than it has between the spring and fall equinoxes, the growing season here. The buds for next year are already formed, however, and await the light and temperature cues which will bring forth more leaves.
Most of a tree's leaves fall on the ground above its roots. These leaves, crunchy and dry at first, insulate the soil. This keeps roots and the soil life on which they depend protected from harsh rains and the winter's alternating freezing and thawing temperatures. The warmth of summer lingers longer in the soil. Eventually, water, age and the decomposers begin to turn leaves into humus, which in turn, provides food and homes for millions of soil organisms. The minerals are then released from the leaves, and become available for use by the tree for another season.
This cycle of growth, death and decay to nourish more growth has gone on for millions of years, slowly building up fertile soil, diverse ecosystems, complicated ecological relationships and metabolic stability.
So let the leaves stay just where they fall! Our society's obsession with raking up, or worse yet, blowing leaves and hauling them away indicates just how far removed people can get from nature's cycles. If you must get rid of leaves, do it quietly and be sure to compost them nearby.
Mowing lawns and raking leaves are very destructive to the great northern forest which once covered this region. This magnificent forest will begin to reemerge if we just let the leaves lie where they fall. Then, you can enjoy the colors on the ground as much as you did on the trees.
This is Bill Duesing, Living on the Earth
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