Easily identifiable by their flaky white bark and yellow fall foliage, birch trees are very common throughout North America. At least 34 different species and their hybrids are present in every state except Hawaii, with the densest concentrations occurring in the moist, temperate northern latitudes. Old World species appear in most states alongside species with restricted ranges, such as the Virginia round-leaf birch (Betula uber). New World and Old World birch species easily hybridize, resulting in specimens that can be difficult to identify.
The most common birch species present in the United States include the river birch (B. nigra), paper birch (B. papyrifera) and the yellow birch (B. alleghaniensis); river birch is the species most commonly sold through commercial nurseries for its value as a mid-sized landscape tree. Several types of birch trees can grow up to 100 feet in height, especially the yellow birch, the primary species used for furniture and other woodworking applications.
Birch trees are primarily multi-stemmed trees, giving them a somewhat shrubby appearance despite their mature height. Even on young trees, many species of birch feature exfoliating bark, or shredded, peeling bark along the trunk and larger limbs of the specimen. With the exception of the dwarf birch (B. nana), many birch species are medium-sized trees, growing to 20 to 50 feet in height.
Soil and Culture Requirements
In nature, birch trees occur primarily in cool, damp climates, growing along river bottoms or in poorly drained soils. Birch trees are susceptible to damage from drought and heat, and perform best when situated along a northern exposure. Grass should be trimmed away from a birch’s root zone, as competition for water can stress the tree. A layer of mulch around the root zone increases the tree’s tolerance for heat and helps keep the root zone cool and moist.
Birches in urban landscapes frequently suffer stress due to improper placement or lack of water, and then fall victim to three common insect pests. The bronze birch borer, as its name implies, is a metallic brown beetle-like insect, roughly 3/8 inch in length and rarely seen. After hatching, larvae chew through the bark to feed on the tree’s vascular tissue. Affected trees exhibit crown dieback and eventually die.
Gypsy moth larvae feed directly on birch leaves, causing defoliation. Birch leaf miners, whose larvae consume the green matter of leaves, are generally not harmful in limited numbers, but trees stressed by heat and drought are more susceptible to the damage caused by leaf miners.
Historic and Modern Uses
Birch products have benefited humans in numerous ways throughout history. Native Americans used the bark of the paper birch to construct shelters, storage containers and sturdy canoes, some examples of which survive even today. The wood, prized for its light color and strength, is still used for furniture, cabinetry and craft woodworking. The sweet-tasting sap is similar to maple sap, and after being boiled into sugar is used to sweeten medicines and to flavor drinks. Birches are also valued among herbalists for the tree’s low-grade content of salicylic acid--the active ingredient in aspirin.