Eileen Berger Indian Trail Master Naturalist
“The autumn leaves drift by my window, those autumn leaves of red and gold” are some of the words to an old song that I am tempted to hum to myself when I notice that the rough-leaf dogwoods, crepe myrtles and sumacs are beginning to show their autumn colors. It’s a little early for many of the other trees in our north Texas area to begin their slow process of color change until they finally drop their leaves.
A great source of information about trees can be found at the U.S. Forest Service website www.na.fs.fed.us. A short review of high school biology reminds us that green plants in general and trees specifically are able to react to sunlight by the process of photosynthesis and create sugars which are then stored in the plant. The green pigment in plants is chlorophyll. Other pigments called carotenoids produce yellow, orange and brown colors in corn, carrots, and daffodils, as well as rutabagas, buttercups, and bananas. The last pigments, anthocyanins, give color to cranberries, red apples, concord grapes, blueberries, cherries, strawberries, and plums. So, all three of these pigments may be present in the leaves of trees.
While the tree is actively growing, the chlorophyll is continually being produced and broken down, and the leaves are green. As the night length increases in the autumn, chlorophyll production slows down and then stops. The carotenoids and anthocyanins that are present in the leaf of the tree are now unmasked and show their colors.
Several factors will affect the amount of fall color we can expect here in the fall. A succession of warm, sunny days and cool nights seem to make for the most fall colors. The warm days spur trees to produce sugar, while the cool nights and the gradual closing of veins in the leaves prevents those sugars from moving out of the leaf. These conditions-lots of sugar and lots of light-spur the production of the anthocyanins. Thus, the leaves display the reds, purples and crimsons vacationers drive hours or days to see. We are at a disadvantage compared to the northeastern portion of the country, since their seasons are more predictable. Hardly anyone travels to Texas to see the fall foliage.
Another factor that affects color is the amount of soil moisture present. Because each year’s weather is different, it is hard to predict exactly when the leaves will be most brilliant. However, I always find it pleasant to take a drive around our older neighborhoods with mature trees, or in the rural areas on some of our back roads, to view the beauty of our own Texas fall foliage before the first cold spell begins to hasten the falling leaves.
If you are a gardener, you probably look forward to the falling leaves for another reason. All that sugar and other nutrients stored in the dead leaves is great for composting, or to keep in bags for use in the garden in the spring. I use leaves between the rows in my vegetable garden, and as mulch. Many butterflies overwinter in leaf litter. Letting some leaves remain under shrubs benefits the butterflies as well as providing mulch. If you think about it, do owners of forests ever fertilize the trees? No, they don’t need to. The deciduous and conifer trees drop leaves, which break down by means of decomposers such as snails, earthworms and microscopic organisms. All those stored nutrients are returned to the soil to be used again. If you ever see a person driving by someone’s house and stopping to gather bags of leaves from the curb, it might be me or another “leaf rustler” taking home treasure to use in my garden. I can’t wait for the leaves to begin falling.