Changing Leaf Color even in South Texas
Ro Wauer, November 9, 2003, The Victoria Advocate, © 2003
Almost everyone admires the beautiful mountainsides and hills of the Western and Eastern states in fall. That is when the leaf colors change from greens to red, browns, and yellows. Golden-colored aspens in the Rocky Mountains can be so spectacular that they become a long-lasting memory. And the changing colors of the eastern maples, oaks, and other broad-leaf trees can beckon us back time and time again. But, even those of us that live in South Texas can get a tiny taste of color from a few of our broad-leafs, representing a change in season that is rather subtle.
Chemistry is most responsible for the color changes. Tree expert Robert Bartlett explained the process this way: "As summer wanes a band of tiny cells at the end of a leaf stem, where it looks like a twig, begin to dry and harden. This stops up the plumbing system inside the leaf. The manufacture of sugar slows down and the green chlorophyll no longer reached the leaves. Now yellow pigments that have been masked within the leaves all summer are revealed. The red pigments are manufactured and the trees take on a kaleidoscope of hues and tones, a harmony of color."
Locally, the nonnative Chinese tallow tree may provide us with considerable color change when its dark green leaves turn to red, yellow, orange, or purple. Color change is also evident in a number of our native species, such as Mexican buckeye, cedar elm, soapberry, sycamore, willows, and a few oaks.
Location and genetics also are significant factors in leaf colors. The southwestern side of a tree usually has a deeper color since it gets more sunshine. Trees in lower places may show color earlier than those in higher spots if cold air settles in the low spots on still nights and the cooler temperatures trap sugar earlier. Generic differences are also important. Typical red leaves are found in maples, dogwoods, and red and scarlet oaks. Browns and oranges are typical for white and black oaks, hickory, and hornbeam, while yellows are more prominent in cottonwoods, pecans, redbud, and elm trees.
Some eastern Native American tribes claimed that leaf changes were due to celestial hunters who killed the Great Bear and that his dripping blood fell onto the forest trees, gradually changing the leaves to various shades. And although "Jack Frost," or the actual occurrence of frost, has little to do with the changing colors, weather is involved. If the fall is rainy, cloudy, or very hot, the foliage generally becomes bland, yellowish, or less vivid. Sugars, which are manufactured by the leaves, are transported down into the trees where they have little effect on fall foliage.
Even though our fall colors are less dramatic than they are to the north, they still represent a change in season, a time to appreciate the end of hot weather and the beginning of mild winter days.