Betula papyrifera

Betula papyrifera is a short-lived species of birch native to northern North America. Paper birch is named after the tree's thin white bark, which often peels in paper-like layers from the trunk. Paper birch is often one of the first species to colonize a burned area within the northern latitudes, and is an important species for moose browsing. Primary commercial uses for paper birch wood are as boltwood and sawlogs, while secondary products include firewood and pulpwood. It is the provincial tree of Saskatchewan and the state tree of New Hampshire.

Description

Betula papyrifera is a medium-sized deciduous tree typically reaching tall, and exceptionally to with a trunk up to in diameter. Within forests, it often grows with a single trunk but when grown as a landscape tree it may develop multiple trunks or branch close to the ground.
Paper birch is a typically short-lived species. It handles heat and humidity poorly and may live only 30 years in zones six and up, while trees in colder-climate regions can grow for more than 100 years. B. papyrifera will grow in many soil types, from steep rocky outcrops to flat muskegs of the boreal forest. Best growth occurs in deeper, well drained to dry soils, depending on the location.

In older trees, the bark is white, commonly brightly so, flaking in fine horizontal strips to reveal a pinkish or salmon-colored inner bark. It often has small black marks and scars. In individuals younger than five years, the bark appears a brown red color with white lenticels, making the tree much harder to distinguish from other birches. The bark is highly weather-resistant. It has a high oil content and this gives it its waterproof and weather-resistant characteristics. Often, the wood of a downed paper birch will rot away, leaving the hollow bark intact.
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 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. The seed production is irregular, with a heavy seed crop produced typically every other year and with at least some seeds being produced every year. In average seed years, are produced, but in bumper years may be produced. The seeds are light and blow in the wind to new areas; they also may blow along the surface of snow.
The roots are generally shallow and occupy the upper of the soil and do not form taproots. High winds are more likely to break the trunk than to uproot the tree.
Genetics and taxonomy

B. papyrifera hybridizes with other species within the genus Betula.
Several varieties are recognized:

B. p. var papyrifera the typical paper birch
B. p. var cordifolia the eastern paper birch ; see Betula cordifolia
B. p. var kenaica Alaskan paper birch ; see Betula kenaica
B. p. var subcordata Northwestern paper birch
B. p. var. neoalaskana Alaska paper birch ; see Betula neoalaskana
Distribution

Betula papyrifera is mostly confined to Canada and the far northern United States. It is found in interior and south-central Alaska and in all provinces and territories of Canada, except Nunavut, as well as the far northern continental United States. Isolated patches are found as far south as the Hudson Valley of New York and Pennsylvania, northern Connecticut, and Washington. High elevation stands are also in mountains to North Carolina, New Mexico, and Colorado. The most southerly stand in the Western United States is located in Long Canyon in the City of Boulder Open Space and Mountain Parks. 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. It may also be associated with big-toothed aspen, yellow birch, Betula populifolia, and maples.
Shrubs often associated with paper birch in the eastern part of its range include beaked hazel, common bearberry, dwarf bush-honeysuckle, wintergreen, wild sarsaparilla, blueberries, raspberries and blackberries, elderberry, and hobblebush.

Successional relationships

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 For example, it is frequently an early invader after fire in black spruce boreal forests. 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.
For example, in Alaskan boreal forests, a paper birch stand 20 years after a fire may have, but after 60 to 90 years, the number of trees will decrease to as spruce replaces the birch. After approximately 75 years, the birch will start dying and by 125 years, most paper birch will have disappeared unless another fire burns the area.
Paper birch trees themselves have varied reactions to wildfire. A group, or stand, of paper birch is not particularly flammable. The canopy often has a high moisture content and the understory is often lush green. As such, conifer crown fires often stop once they reach a stand of paper birch or become slower-moving ground fires. Since these stands are fire-resistant, they may become seed trees to reseed the area around them that was burned. However, in dry periods, paper birch is flammable and will burn rapidly. As the bark is flammable, it often will burn and may girdle the tree.

Wildlife

Birch bark is a winter staple food for moose. The nutritional quality is poor because of the large quantities of lignin, which make digestion difficult, but is important to wintering moose because of its sheer abundance. Moose prefer paper birch over aspen, alder, and balsam poplar, but they prefer willow over birch and the other species listed. Although moose consume large amounts of paper birch in the winter, if they were to eat only paper birch, they may starve.
Although white-tailed deer consider birch a "secondary-choice food," it is an important dietary component. In Minnesota, white-tailed deer eat considerable amounts of paper birch leaves in the fall. Snowshoe hares browse paper birch seedlings, and grouse eat the buds. Porcupines and beavers feed on the inner bark. 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.

Conservation

As of 2023, the conservation status of paper birch is considered of least concern according to the International Union for Conservation of Nature. However, the species is considered vulnerable in Indiana and Nebraska, imperiled in Illinois, Virginia, and West Virginia, and critically imperiled in Colorado and Tennessee. These areas represent the southerly and southwesterly edge of the paper birch's range.

Uses

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, plywood, and oriented strand board. The wood can also be made into spears, bows, arrows, snowshoes, sleds, and other items. When used as pulp for paper, the stems and other nontrunk wood are lower in quantity and quality of fibers, and consequently the fibers have less mechanical strength; nonetheless, this wood is still suitable for use in paper.
The sap is boiled down to produce birch syrup. The raw sap contains 0.9% carbohydrates as compared to 2 percent to 3 percent within sugar maple sap. The sap flows later in the season than maples. Currently, only a few small-scale operations in Alaska and Yukon produce birch syrup from this species.