Betula papyrifera (paper birch, also known as (American) white birch It is the provincial tree of Saskatchewan and the state tree of New Hampshire.

Description

thumb|Leaves are doubly serrated with sharp teeth.

Betula papyrifera is a medium-sized deciduous tree typically reaching tall,

  • In older trees, the bark is white, commonly brightly so, flaking in fine horizontal strips to reveal a pinkish or salmon-colored inner bark.
  • The leaves are dark green and smooth on the upper surface; the lower surface is often pubescent on the veins. They are alternately arranged on the stem, oval to triangular in shape, long and about two-thirds as wide. The leaf is rounded at the base and tapering to an acutely pointed tip. The leaves have a doubly serrated margin with relatively sharp teeth. Each leaf has a petiole about long that connects it to the stems.
  • The fall color is a bright yellow color that contributes to the bright colors within the northern deciduous forest.
  • The leaf buds are conical and small and green-colored with brown edges.
  • The stems are a reddish-brown color and may be somewhat hairy when young.
  • The flowers are wind-pollinated catkins; the female flowers are greenish and long growing from the tips of twigs. The male (staminate) flowers are long and a brownish color. The tree flowers from mid-April to June depending on location. Paper birch is monoecious, meaning that one plant has both male and female flowers.
  • The fruit matures in the fall. The mature fruit is composed of numerous tiny winged seeds packed between the catkin bracts. They drop between September and spring. At 15 years of age, the tree will start producing seeds but will be in peak seed production between 40 and 70 years. This is an isolated Pleistocene relict that most likely reflects the southern reach of boreal vegetation into the area during the last Ice Age.

Ecology

In Alaska, paper birch often naturally grows in pure stands by itself or with black or white spruce. In the eastern and central regions of its range, it is often associated with red spruce and balsam fir.

Successional relationships

thumb|Prescribed fire in a black spruce-paper birch-quaking aspen community in boreal Alaska

Betula papyrifera is a pioneer species, meaning it is often one of the first trees to grow in an area after other trees are removed by some sort of disturbance. Typical disturbances colonized by paper birch are wildfire, avalanche, or windthrow areas where the wind has blown down all trees. When it grows in these pioneer, or early successional, woodlands, it often forms stands of trees where it is the only species.

Paper birch is considered well adapted to fires because it recovers quickly by means of reseeding the area or regrowth from the burned tree. The lightweight seeds are easily carried by the wind to burned areas, where they quickly germinate and grow into new trees. Paper birch is adapted to ecosystems where fires occur every 50 to 150 years As paper birch is a pioneer species, finding it within mature or climax forests is rare because it will be overcome by trees that are more shade-tolerant as secondary succession progresses. The seeds of paper birch are an important part of the diet of many birds and small mammals, including chickadees, redpolls, voles, and ruffed grouse. Yellow bellied sapsuckers drill holes in the bark of paper birch to get at the sap; this is one of their favorite trees for feeding on. These areas represent the southerly and southwesterly edge of the paper birch's range.

Uses

thumb|Paper birch at [[Acadia National Park in Maine, informally referred to as "white birch"]]

Betula papyrifera has a moderately heavy white wood. It makes excellent high-yielding firewood if seasoned properly. The dried wood has a density of and an energy density . Although paper birch does not have a very high overall economic value, it is used in furniture, flooring, popsicle sticks, pulpwood (for paper), plywood, and oriented strand board. In the Ashinaabe language birch bark is called wiigwaas.

Plantings

Paper birch is planted to reclaim old mines and other disturbed sites, often bare-root or small saplings are planted when this is the goal. B. papyrifera is more resistant to the bronze birch borer than Betula pendula, which is similarly planted as a landscape tree.

Pests

Bronze birch borer is a major pest among birch species. Under repeated infestation or stress to the tree from other sources, bronze birch borers may kill the tree. The insect has a D-shaped emergence hole where it chews out of the tree. Healthy trees are resistant to the borer, but when grown in less than ideal conditions, the defense mechanisms of the tree may not function properly. Chemical controls exist. Upon hatching, the larvae feed on the undersides of the leaves and cause browning. It was introduced to the United States in the 1920s.