Dr. Ellen Moody
One of natures splendors is its display of colors. In order to observe the colorful trees, I arranged to take several trips to Shenandoah National Park in the month of October. The park lies in the western portion of the state of Virginia, near Washington D.C. In Shenandoah National Park, varieties of outdoor plants helped me to observe the discoloration of different trees in the fall. When you think of autumn, you probably imagine walking along tree lined lanes and golden leaves crunching under your feet. On my first visit, as I was walking in the park, it seemed trees are the giants of the kingdom of plants. Throughout the park, observers can find a wide range of trees from many different species. Trees and shrubs stand as a canopy over most other forms of terrestrial life, and they characterize and control the natural communities of which they themselves are a part. Walking in the park over the past week or two has provided me some good with opportunities to observe the change of season as nature put on a memorable show of colors. Although colorful leaves on half-bare branches of tree contribute a significant beauty to nature, careful, close, and scientific observation helps us to appreciate the beauty of autumn more.
As a child raised by parents whose passion was gardening, I learned early on to distinguish maples, oaks, and ashes among other trees. In the park, while I was looking for more colorful trees, I found a few sweet gum trees and several pine oak trees with attractive red leaves. I realized the majority of trees were from the maple family such as red maple or silver maple. Maple trees are medium-sized trees with smooth gray bark with opposite lobe leaves. In the fall, every observer is able to see the structure of the tree by looking at the half-bare branches. The structure of the trees shows their contribution in making a cold shade in hot days of summer.
As I was walking up the hill, I saw a large population of ash trees. Among all of those types of trees in the Shenandoah National Park, the White Ashes ( Fraxinus Americana), located on top of the hill, had a unique effect on the whole scene (1). White ashes are very widely distributed trees which reach a height of 120 to 130 feet. Fall foliage color on many specimens began as yellow, and then morphs to purple. I think they were especially attractive when they were at an in-between stage: a mix of yellow and purple. However, the fall foliage of white ashes could be short-lived.
It seemed white ashes were an upland trees with twigs that had the brown side buds usually set in deep U-or V-shaped notched in the upper edge of leaf scars. It seemed the weather was cold for those little buds to survive. I found bunches of their old fruits on the ground, which were narrow and winged structures one to two inches long that hung in dense clusters. While I was observing, many small creatures moved down from the tree to find food and return to care for their young.
I climbed and touched the twigs. The twigs were round and either hairless or velvety. Most of the leaves were toothed and stalked. Beneath the leaves had lighter colors and trunk bark was rather dark and tight with rigid interwoven pattern of shallow ridges. The large leaves were in pairs and are divided usually into seven toothed, oval-pointed segments. One of the significance of white ashes is the compound and oppositely arranged of its leaves (1). These leaves are 8" to 13" in length with 7 to 12 leaflets per leaf. Leaflets measure 2" to 4" long and are usually oval shaped. The tops of the leaves are dark green and shiny where the bottoms of the leaves are pale green with tiny hairs. In the second visit of my observation, all of the dark green leaves transformed into light orange and yellow. It was amazing that in a short period of time which was just about seven days, leaves turned into different colors. I wonder what could cause the colors of leaves to change so quickly.
According to the National Audubon Society, identification of many trees is based on leaf characteristics which have observed in different seasons. By observing the warm splashes of vivid reds, yellows and oranges in the mountain regions in the Shenandoah National Park, observers may wonder how a green leaf can turn into variety of colors in just few weeks.
The coloration of leaves differs from one region to another. In the area that gets cold very quickly, the progress of coloration of leaves happens faster. There is some degree of differentiation between individuals, possibly due to the amount of light and shade they get at their particular location, health of the individuals, or even the amount of cloud cover during a season (2). In my second visit of the park, I noticed a major decrease in the number of leaves that were hanging off the trees. In the past few weeks different factors caused these changes. For instance, a large amount of leaves were taken of the tree in just one windy day. Few days after rain was pouring and caused loosing a large number of yellow and brown leaves.
Based on many different biochemical and biosynthesis changes of pigments, coloration of leaves occur. Dormancy is a period in a plant's life of decreased metabolism (2). In the deciduous hardwoods of the temperate regions, this period is usually referred to term "winter "(2). In preparation for winter and to prevent or minimize damage from cold, plant cells switch from production of chlorophyll for growth, to production of sugars and amino acids, which act as antifreeze for the plant. As the plants ability to synthesize chlorophyll becomes reduced, and yellow and orange carotinoids and xanthophylls, always present within the leaf, begin to show. Also senescing cells produce other chemicals, particularly anthocyanins, responsible for red and purple colors (3). Leave colors are produced by three main classes of pigments, the green chlorophylls, the yellow to red carotenoids and the red, blue and violet anthocyanins (3). As fall arrives, the days become cooler and shorter and the leaves begin to slow down their chlorophyll production. Sugar remaining in the leaves combines with other substances, and the leaves show their spectacular red and gold colors of fall.
As the weather began to get cold and darker, I took my last picture of a yellow ash, which was standing tall and quiet waiting for the next wind to touch its bare branches. What I was witnessed in the past few weeks, happens once a year, but the chance of observing trees in a natural habitat especially in the fall closely and scientifically was a unique opportunity. Appreciation of and pleasure from colorful trees are far more easily fostered when some scientific observation of their characteristics is gained.