Science has always fascinated me. This includes not only the ecological sciences, which I studied in school, but other endeavors, as well.
Overview of the White Birch and Quaking Aspen
To anyone who has viewed the spectacular color landscapes often featured in the publications of some of our more noted environmental organizations has probably noticed the remarkable images made in extensive forests of white-barked trees. Depending on the locale, these forests might consist of either quaking aspen or white birch, and since both trees turn a brilliant yellow during autumn, a close look at the leaf might be necessary to determine which tree is present.
What Is Dendrology?
Of course, there is a name for the process of identifying trees and other woody plants by their physical features. This science is called dendrology. Just in case you have not heard of dendrology, here is a simple, succinct definition from the North Carolina Forestry Association. Dendrology is the study of the characteristics of woody plants to distinguish between species.
Most commonly, the characteristics of the plant leaf (or needle) are closely examined in order to make a positive identification of the tree. Also important to the dendrologist are the flower, fruit and habitat of the tree. These features can be handy in identifying the tree in winter when leaves may not be present.
Learning to Identify Similar Species
Not too long ago during my summer travels I was riding through Northern Minnesota, when my traveling companion pointed out that the forest was filled with many trees displayed a light-colored bark. Upon closer examination we discovered two types of trees growing alongside the road.
They were the white birch (Betula papyrifera) and the quaking aspen (Populus tremuloides). From a distance these two trees look very similar, especially since they both have light-colored bark. However, in the upper Midwest and many other places along the Canadian border, these two trees actually can be found in the same woodlot, so learning to tell the birch from the poplar requires some basic botanical skills.
Latin Names and Meanings
Since most wild woody plants have various and sometimes overlapping common names, scientific classification is done in Latin. Each species of plant is labeled by its genus, which is capitalized, and species, which is written in lower case. The genus always precedes the species designation. Furthermore, species designation though in Latin, usually portrays a descriptive attribute of the tree.
For example, the paper birch (Betula papyrifera) has a species name of papyrifera. At first glance, this word seems like pure nonsense, but actually the scientific term is a direct reference to Egyptian papyrus, an early form of paper. Anyone familiar with the paper-like bark of this birch tree will immediately recognize the comparison.
On the other hand, the tremuloides in the quaking aspen scientific name refers to the act of trembling, a condition the leaf exhibits, when it twists and turns in a gentle breeze.
Habitat Is Important
Since both these trees often share the same ecological niche, it is important to note the growing habits of each. Essentially both trees are shade intolerant pioneers that frequently invade disturbed sites, especially after a fire or flood. The result of these invasions can produce even-aged stands of either tree or a even-aged mixed stand. Both trees prefer moist, nutrient-rich soils and will not grow in the shadow of their own kind.
Though both these trees can form large stands, especially after a natural disturbance like a fire, the aspen stands can be quite extensive. This is especially true in the higher elevations of the Rocky Mountains, where these stands can stretch for miles underneath the higher peaks.
Using a Dichotomous Key
One of the biggest aids in identifying leafy plants is the dichotomous key. Dichotomous keys are used in many aspects of scientific identification, where they are used to identify a plant or animal in which each stage presents descriptions of two distinguishing characters, with a direction to another stage in the key, until the species is identified.
When identifying trees and shrubs in this matter, one usually begins with noting whether the plant has leaves or needles, such as those found on conifers. From this starting point, the key is used to separate the plant into families. With the paper birch, the identifier will be eventually directed to the birch family of trees and shrubs (Betulaceae), which also includes alders, hazels and hornbeams.
In the case of the quaking aspen, the botanical sample will be placed in the Willow family (Salicaceae). Along with the willow, there are also poplars, cottonwoods and aspens in this extensive grouping of flowering plants.
One word of caution should be used here. Not every tree commonly referred to as a poplar, will be correctly identified as a member of the Willow family. The yellow poplar comes to mind, for it is placed in the Magnolia family, despite being often referred to as a poplar.
The Different Leaves
A close-up examination of the leaf is an excellent way to tell the two trees apart. Not only are the leaves a different shape, but they also have a different type of leaf margin. The white birch has an ovate or spear-shaped leaf with a double-serrated edge or leaf margin.
On the other hand the leaf of the quaking aspen is more heart-shaped leaf with small rounded teeth. These noticeable differences make identification of each tree relatively straightforward, as long as the leaves are out. During the winter months, other parts of the tree should be looked at to determine species.
From a distance the bark of both trees seem very much the same, but when up close, color and markings can be used to tell a white birch from a quaking aspen.
First of all the birch bark of Betula papyrifera is really white, while the aspen tree usually carries a distinct tint of green on its trunk exterior. Also, the birch bark often naturally hangs off the tree, like a piece of loose paper, while the aspen bark surrounds the tree tightly, like a snake skin. Incidentally, the bark of the paper or white birch is often prized for many craft projects, including canoe-making, picture framing and decorative patches on furniture.
Fruit and Flower
Finally there is the seed-producing fruits of each tree, which may be the most distinctive of these features. The birch produces male and female flowers on the same tree in the forms of catkins, which are long pendant, flowering structures of two to four inches that hang down from the tree. Eventually, these yield heart-shaped, winged nutlets attached to tiny oval seeds.
In comparison, the aspen also produces male or female flowers in catkins, but each tree contains either all male or all female flowers. This condition is referred to as dioecious, compared to the monoecious paper birch, where male and female flowers occur on the same tree. The seeds of the aspen are very small and are born in a small capsule.