Neil I. Lamson
Sweet birch (Betula lenta), also commonly referred to as black birch or cherry birch, was at one time the only source of oil of wintergreen. It is the aroma of wintergreen emanating from crushed leaves and broken twigs to which this birch owes its common name, sweet. Its specific name, lenta, is derived from the tough yet flexible twigs that characterize the species. The wood is also unique. When exposed to air it darkens to a color resembling mahogany and, in times past, was used as an inexpensive substitute for the more valued tropical wood.
Regularity: Regularly occurring
Regularity: Regularly occurring
-The native range of sweet birch.
Soils and Topography
Sweet birch grows over a wide range of altitudes from near sea level along the New England coast to an upper extreme of 1220 to 1370 m (4,000 to 4,500 ft) in the southern Appalachian Mountains. In New England, the species is fairly common in southern Maine, the highlands of New Hampshire, western Vermont, the highlands of Massachusetts and Rhode Island, and throughout Connecticut. In the southern Appalachians, where sweet birch grows best, the optimum elevation is between 610 and 1370 m (2,000 and 4,500 ft).
Moist, protected northerly or easterly slopes are considered most favorable for sweet birch in both northern and southern parts of its range.
Associated Forest Cover
19 Gray Birch-Red Maple
20 White Pine-Northern Red Oak-Red Maple
21 Eastern White Pine
22 White Pine-Hemlock
24 Hemlock-Yellow Birch
25 Sugar Maple-Beech-Yellow Birch
27 Sugar Maple
28 Black Cherry-Maple
39 Black Ash-American Elm-Red Maple
58 Yellow-Poplar-Eastern Hemlock
59 Yellow-Poplar-White Oak-Northern Red Oak
In the southern Appalachian region, sweet birch reaches its best development in Types 21, 22, 25, 57, 58, and 59.
Important associated tree species include yellow-poplar (Liriodendron tulipifera), basswood (Tilia spp.), white ash (Fraxinus americana), sugar maple (Acer saccharum), red maple (A. rubrum), northern red oak (Quercus rubra), white birch (Betula papyrifera), gray birch (B. populifolia), hemlock (Tsuga spp.), and eastern white pine (Pinus strobus). Understory vegetation varies with locality, but commonly associated shrubs are mountain maple (Acer spicatum), striped maple (A. pensylvanicum), flowering dogwood (Cornus florida), downy serviceberry (Amelanchier arborea), American hornbeam (Carpinus caroliniana), and eastern hophornbeam (Ostrya virginiana). Associated herbaceous vegetation includes Solomons-seal (Polygonatum pubescens), marsh blue violet (Viola cucullata), clubmosses (Lycopodium spp.), mayapple (Podophyllum peltatum), trilliums (Trillium spp.), jack-in-the-pulpit (Arisaema atrorubens), and a variety of ferns. In former clearcut areas where young stands are established, blackberry (Rubus spp.) is abundant.
Diseases and Parasites
Sweet birch does not seem to be very susceptible to winter killing. The severe winter of 1942-43 partly or completely killed trees of many species in Maine, but sweet birch appeared to be uninjured (7).
A study of the effects of the 1930 drought on oak forests in central Pennsylvania indicated that sweet birch is intermediate in drought resistance. Drought caused mortality reduced basal area by 36 percent, for sweet birch, 11 percent for sugar maple, 50 percent for red maple, and 15 percent for white ash (7).
Several fungi attack living sweet birch trees, and sterns frequently become highly defective at an early age. In unmanaged sawtimber stands in the anthracite, region of Pennsylvania, cull exceeded 20 percent of' the total cubic-foot volume of trees 43 cm (17 in) in diameter on Site 1 and 23 cm (9 in) on Site II (7). The most important pathogens are, white trunk rot (Phellinus igniarius), yellow cap fungus (Pholiota limonella), and Nectria canker (Nectria galligena) (5). Sweet birch is one of the most susceptible species to Nectria canker. Cankers on the bole are more serious than branch cankers because they reduce merchantable volume and increase susceptibility to stem breakage.
Sweet birch is easily damaged by ground fires because it has extremely thin bark. Several fires may kill the tree, but even light scorching at the base of the tree will lower its resistance to the attacks of various diseases or insects such as the ambrosia beetle (Xyloterinus politus) (9).
Several leaf-feeding insects occasionally infest sweet birch. The most prevalent ones are birch tubemaker (Acrobasis betulella), birch skeletonizer (Bucculatrix canadensisella), orientalmoth (Cnidocampa flavescens), gypsy moth (Lymantria dispar), and dusky birch sawfly (Croesus latitarsus) (6).
Reaction to Competition
Life History and Behavior
In nursery practice, birch seed is usually sown in the fall after collection in the late summer or fall. Seeds are broadcast and covered as lightly as possible or not at all if the seedbed is to be kept moist. Epigeal germination is usually complete 4 to 6 weeks after sowing.
Seedlings require light shade for 2 to 3 months during the first summer. Tree percent is low; only 10 to 20 percent will produce 1-0 seedlings. Desirable seedling density is 270 to 485/m² (25 to 45/ft²). Usually 1-0 and 2-0 barerooted seedlings are planted (1).
Sweet birch seedlings develop best during their early years when protected by side shade or light overhead shade. Scattered individuals frequently grow as advance reproduction in openings in mature stands or under younger stands of light to moderate crown density. In the Harvard Forest, sweet birch is sometimes present in the advance hardwood growth under old-field white pine about 50 to 70 years old (7). On fairly cool, moist sites-sheltered ravines, north to east aspects, or moderately heavy soils-heavy cutting or clearcutting of these stands generally results in a higher proportion of sweet birch in the succeeding reproduction than was present in the advance growth. On the other hand, studies in northwestern Pennsylvania have shown that clearcutting of immature second-growth northern hardwood stands before an understory has developed is followed by an abundance of intolerant species with only a poor representation of sweet birch and tolerant hardwoods (7).
Seed Production and Dissemination
Recommended storage conditions for birch seeds are 1 to 3 percent moisture content at 2° to 3° C (36° to 38° F) (1). Stratification does not generally improve germination, but best germination is obtained when seeds are tested under light (1).
Flowering and Fruiting
Growth and Yield
On the very best sites, sweet birch grows 21 to 24 m (70 to 80 ft) tall and 61 to 152 cm (24 to 60 in) in d.b.h. In most areas, however, it is a tree of medium size, 15 to 18 m (50 to 60 ft) tall and 61 cm (24 in) or less in diameter. One of the largest trees on record is 147 cm (58 in) in d.b.h. and 21 m (70 ft) tall.
According to a study in virgin hemlock-hardwood stands in northwestern Pennsylvania, sweet birch saplings in the understory grow about twice as fast as hemlock, beech, sugar maple, and red maple slightly faster than yellow birch, and at about the same rate as black cherry (Prunus serotina) (7).
Data from plots on apparently average sites in Delaware County, NY, and Forest and Potter Counties, PA, show that sweet birch can attain a diameter at breast height of about 10 cm (4 in) in 20 years, 18 cm (7 in) in 40 years, and 25 cm (10 in) in 80 years (7). In unmanaged sites in the anthracite region of Pennsylvania, sweet birch reached 36 cm (14 in) d.b.h. in 85 years on high sites (Site 1) and 30 cm (12 in) in 80 years on average sites (Site 11). It is estimated that in managed stands, the same sizes would be reached in 10 to 15 years less time (7).
In the Pennsylvania anthracite region, periodic cubic volume production begins to decline when the trees are 36 to 41 cm (14 to 16 in) in d.b.h. (7); that is, in about 100 years. Older trees are common and two individuals 192 and 265 years old have been found in Pennsylvania (7).
Molecular Biology and Genetics
Virginia round-leaf birch, Betula uber, at one time was classified as Betula lenta var. uber. The known population of this species consists of 12 mature trees, 1 sapling, and 21 seedlings in Smythe County, VA (10). In 1978, it was officially listed as an endangered species.
A natural hybrid of Betula lenta and B. pumila that occurred at the Arnold Arboretum was designated B. jackii.
Barcode data: Betula lenta
Statistics of barcoding coverage: Betula lenta
Public Records: 4
Specimens with Barcodes: 6
Species With Barcodes: 1
National NatureServe Conservation Status
Rounded National Status Rank: N1 - Critically Imperiled
Rounded National Status Rank: N5 - Secure
Relevance to Humans and Ecosystems
Betula lenta (sweet birch, also known as black birch, cherry birch, mahogany birch, or spice birch) is a species of birch native to eastern North America, from southern Maine west to southernmost Ontario, and south in the Appalachian Mountains to northern Georgia.
Characteristics and habitat
Betula lenta is a medium-sized deciduous tree reaching 20 m (66 ft) tall with a trunk up to 60 cm (2.0 ft) diameter. In younger trees the bark is characteristic of most birches, with smooth bark and distinct horizontal lenticels. It is sometimes mistakenly identified as a cherry tree. In some older tree specimens the bark can (unlike most birches) develop vertical cracks into irregular scaly plates revealing rough darkish brown bark patterns. This, however, does not occur in all specimens. The twigs, when scraped, have a strong scent of wintergreen due to methyl salicylate, which is produced in the bark. The leaves are alternate, ovate, 5 to 10 cm (2.0–3.9 in) long and 4 to 8 cm (1.6–3.1 in) broad, with a finely serrated margin. The flowers are wind-pollinated catkins 3 to 6 cm (1.2–2.4 in) long, the male catkins pendulous, the female catkins erect. The fruit, maturing in fall, is composed of numerous tiny winged seeds packed between the catkin bracts. Seed production mainly occurs in trees that are between 40 and 70 years old, although light crops may occur as early as 20 years. The average lifespan of B. lenta is 100 years, with a maximum of 150.
Betula lenta was used commercially in the past for production of oil of wintergreen before modern industrial synthesis of the oil; the tree's name reflects the wintergreen scent of the shoots.
The sap flows about a month later than maple sap, and much faster. The trees can be tapped in a similar fashion, but must be gathered about three times more often. Birch sap can be boiled the same as maple sap, but its syrup is stronger (like molasses).
Betula lenta's leaves serve as food for some caterpillars (see List of Lepidoptera that feed on birches) and the solitary leaf-cutter bee Megachile rubi cuts pieces from the leaves to line the cells of its nest.
- Eickwort, George C.; Matthews, Robert W.; Carpenter, James (1981). "Observations on the Nesting Behavior of Megachile rubi and M. texana with a Discussion of the Significance of Soil Nesting in the Evolution of Megachilid Bees (Hymenoptera: Megachilidae)". Journal of the Kansas Entomological Society 54 (3): 557–570. JSTOR 25084194.
Native Americans used Betula lenta medicinally to treat dysentery, colds, diarrhea, fevers, soreness, and milky urine, and as a spring tonic.
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