All birch trees are of the genus Betula, which is related to the beech/oak family of trees. The birches include about 100 species that naturally inhabit the cooler northern climates. Most of the species are shrubs. Of the trees that exist, all are identified by the presence of a paper-like peeling bark. Depending upon the type of birch, the bark can be white, silver or variations of both, developing into dark gray to black markings or horizontal streaks of gray as the tree ages. The bark on older trees is much darker than on young trees.
Most birch leaves are 2 to 3 inches long and have a characteristically oval leaf base; the edges of the leaves are serrated or saw-toothed. Birch trees have both male and female flowers called “catkins” that appear on the same tree. Male catkins droop, are about 1 1/4 inch long, form in the fall and remain on the tree through the winter, never opening until late April or May. Female catkins make their appearance in the spring right along with the new tree shoots. They stand upright and grow up to 1 inch long. Female catkins elongate and form hanging catkins that contain hundreds of tiny seeds, which are scattered on the wind. Birches are comparatively short-lived trees, dying off, rotting and enriching the soil to repopulate new, open areas. They are particularly adept at repopulating burned areas.
The downy birch has simple leaves characterized by a triangular shape with rounded corners and a very jagged leaf edge. The young twigs are covered with tiny hairs, the buds are prominent on the slender twigs and the buds may be sticky. The downy birch bark is normally bright-colored. The young stems may be red, turning to white/silver with age. The bark then develops markings of dark gray and black, making the tree trunk and bark much darker as the tree ages.
The bark on the white birch turns white as the tree matures. The tree usually reaches a height of 40 to 50 feet and has a spread of 20 to 30 feet. The white birch normally has three or four separate trunks. The tree prefers full sun and its leaves, which are normally dark green, turn golden in the fall. White birches bloom in the summer and produce small, nutlet fruit.
The paper birch is found in the northernmost forests and river valleys. Full-grown trees reach a height of approximately 30 to 33 feet and have a habit of growing upright. Paper birches often grow as a clump of three or more main trunks. Mature trees have a white, papery bark that peels away to reveal an attractive underside for both summer and winter landscapes.
European Weeping Birch
A graceful, weeping form is typical of the European weeping birch, the largest of the birches. Fully grown, these trees can reach nearly 53 feet tall. The youngest twigs, which drape at the ends of the branches, account for the weeping form of the tree. The leaves are deeply cut, giving the tree a lace-like appearance.