Cool November temperatures, high winds and damp gloom have arrived, and darker, colder days are approaching. As the natural world brings fall reminders of the rapidly passing seasons, our native trees and shrubs gently reveal the ancient wisdom of synchrony, adaptation, and preparation for the winter challenges ahead.
How do maples, oaks, cherries, dogwoods and sumacs survive the long icy months ahead? These native woody plants are very adapted to the changing seasons and prepare for the worst of winter since the summer solstice! It was then, in mid-summer, that a series of key changes began, gradually leading to the protective state of cold-hardiness, sluggish metabolism, and a quiescence known as winter dormancy. Dormancy ensures survival during harsh times of winter, when soils are frozen, high winds and extremely cold temperatures, but critical preparations must begin well in advance. Although we don’t see any obvious outward changes, woody plant dormancy is initiated when blue-colored leaf pigments, called phytochromes, detect changes in the photoperiod starting in late June. Although most humans tend not to notice it, this is when the nights start to get longer and the days get shorter, very subtly. The plant’s biochemical clock is particularly sensitive to the change in the length of the night, which in turn triggers chemical messengers and hormonal changes in preparation for the difficult season ahead.
At the end of summer, the preparations of the plants become more apparent to man. Small buds have already formed along the twigs, containing the miniature flowers, cones and leaves of next spring wrapped in protective, waxy, waterproofed bud scales. Deciduous trees, which shed their leaves in the fall, began to mobilize sugars and other valuable materials out of the foliage and into the trunk and roots for winter storage. The leaves initially retain their familiar green color, due to the predominance of the photosynthetic pigment chlorophyll, while other colorful molecules such as orange carotenes, yellow xanthophylls, and red and purple anthocyanins are vastly outnumbered and obscured by the green. However, as the nights lengthen and temperatures drop, the chlorophylls break down and the cell chemistry of the leaves is altered, revealing and intensifying the spectacular radiance of fall beauty. The golden yellows of aspen, birch, larch and poplar, the tan oranges of ash, hickory, oak and beech, and the rich purples, scarlet and burgundy of maple, dogwood, cherry and beech. sumac bless human viewers with a breathtaking symphony of color, hue and texture, but for trees, it’s all about timing and preparation for the challenges ahead. The colors fade and the fall of the leaves follows. The leaves, now brown, dry and devoid of nutrients and water, fall off with the next gust of wind, rain or snow, and will nourish the soils in which they rest.
It is estimated that about ten million leaves fall from an acre of trees each year, or about 50,000 to 70,000 leaves per tree. But why is such a huge loss necessary? While it may at first seem like nature’s extravaganza, leaf fall is actually another strategy for dormancy preparation and winter survival. To understand this, remember that the most important function of leaves is to provide a large surface to catch light, which in turn drives the food machinery of all green plants. The thin and wide sheets are beautifully designed to efficiently absorb a huge amount of sunlight, but at the same time are the site of great water loss through evaporation. In the summer, an acre of forest can lose up to 2,500 gallons of water per day, which is good as long as plant roots can replace the lost water by soaking up more of the soil. Winter, however, poses new problems, not so much because of the cold, but because water is no longer available for absorption – it gets stuck in the ground in frozen form. If the leaves were to remain on the trees all winter, devastating desiccation would occur. Rather than sustaining tissue damage or dying from dehydration, deciduous trees drop their leaves, minimize their water loss, and in their dormant state patiently wait for the warmth and light of spring.
The Chautauqua Watershed Conservancy is a non-profit organization whose mission is to preserve and improve the water quality, scenic beauty and ecological health of lakes, streams, wetlands and watersheds in the region of Chautauqua. For more information, visit chautauquawatershed.org and follow us on Facebook and Instagram.