Betula neoalaskana

(resin birch)

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Photo of Betula neoalaskana by Celia Hampton Miller

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                            Species Description
                            Phenology
                            Reproduction
                            Insects/Disease/Pathogens
                            Known Uses/Ethnobotany
                            Species Distribution
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Betula neoalaskana (resin birch) is the most abundant deciduous tree in Alaska, occurring across forested regions of Denali (especially after fires) and rarely in subalpine sites. Mature trees are instantly recognizable for their straight, pale trunks with papery, peeling bark. Individuals grow up to 25 m tall, typically forming slender crowns in forests, or more branched and rounded if grown in open conditions.

When young, trees are brown-pink barked, maturing to silver-white or cream-pink. The paper-textured bark is smooth, marked with faint horizontal lines (lenticels); peeling off in long, curling strips, and interrupted on the trunk by many dark branch scars. Resin birch twigs are red-brown and covered with small white spots, resin glands.

The leaf shape is deltoid-ovate, the base round to wedge-shaped, with doubly serrate teeth and a long, narrow tip. The back of the leaf is dotted with glands, and the lower veins are typically hairy.

Betula neoalaskana produces small pendant catkins very early in spring, male and female on the same twig. Male catkins are 2.5-4 cm long, with each flower consisting of a calyx and two stamens. Female catkins are short (1-2 cm long) and cylindrical (0.5-1 cm wide), with numerous tiny flowers, each having one ovary and two styles. Seeds are small, and have two papery wings to catch the wind, wings wider than the body.

Young resin birch trees can be confused with alder (Alnus). Those shrubs never have papery, peeling bark, their leaves are larger, ovate (not deltoid) and the twigs are not dotted with resin glands. Trees of the genus Populus can at first glance look like resin birch, but, among other characters, their bark is never papery and peeling.

Leaf buds and male catkin buds are developed in the summer and over-winter. In the spring, the male catkins expand and open while female catkins grow, flowering in late spring, before the leaves open. In central Alaska, birches green-up around mid-May, and senescence begins in late August or early September. Numerous tiny winged seeds are released in October or November, usually after snowfall in interior Alaska, yielding a 'rain' of brown nutlets across birch-forested areas. The seeds can be blown across the top of the snowpack, increasing the distance from the parent tree (Uchytil 1991). Seeds are dormant through winter and germinate in spring. Resin birch is fast-growing but short-lived, and trees are highly shade intolerant. Vertical growth stops after 60 or 70 years, and the upper age limit is 140 years. In forest succession in interior Alaska, resin birch is overtaken by longer-lived conifers within 80 years after establishment.

Betula neoalaskana is monoecious, but with separate male and female catkins. Male and female are often produced on the same twig. Flowers are wind-pollinated. Seeds are small, and have two papery wings to catch the wind. Birch trees will sprout abundantly from the stump after logging or fires (Uchytil 1991). Seeds germinate best on a mineral seedbed, and extremely high germination rates are found in post-burn areas after high to moderate severity fires. In Denali, resin birch has the second highest number of seedlings in burned plots, after black spruce (Roland et al. 2013).

Betula neoalaskana is browsed by moose, snowshoe hare and other herbivores. One name for this species is 'resin birch', referring to the many glands it has to produce herbivory-deterring compounds. Concentrations of these compounds are particularly high within Alaskan trees (Bryant et al. 1984). There are various insects that feed upon B. neoalaskana including (but not limited to): leaf rollers (Epinotia solandriana), the birch leaf miner (Fennusa pusilla, leaf beetles (Chrysomela spp.), and the birch aphid (Euceraphis betulae)(Holsten et al. 2001). Some of the common fungal pathogens of B. neoalaskana include: the birch conk (Piptoporus betulinus), birch leaf rust (Melampsora betulinum), birch canker (Nectaria galligena), and cinder conk (also known as chaga, Inonotus obliquus)(Holsten et al. 2001).

Slabs of this hardwood's papery waterproof bark have been used extensively in construction of boats and baskets. Wood is used for fuel, as well as cabinetry, furniture, bowls and other hand-crafts. The bark of resin birch is widely used for baskets by Alaska Natives in the interior. Birch leaf tea is used to aspirin-like effect, the sap is as a tonic or wash on skin problems including sores, and the bark is brewed in tea or chewed for fighting fevers and colds (Garibaldi 1999). Birch leaves can be eaten in spring, and the sap can be tapped in early spring and extensively boiled to make syrup.

Disclaimer for Known Uses.

Resin birch is a North American species of the boreal zone, occurring from Alaska eastwards to Ontario. Resin birch is widely distributed in Alaska, with its range reaching into southern valleys of the Brooks Range, to southwest Alaska in Wood-Tikchik State Park and across southcentral Alaska, including Kodiak. In Denali, B. neoalaskana occurs most frequently around the lowland basins and hills, on both sides of the Alaska Range. Though one of the more common tree species in the park, its distribution is patchy, and it rarely forms pure stands perhaps because resin birch establishes best in burned areas post-fire.

Details are shown in the Plots & Charts found at right, depicting recent Denali data.

Though this species has been found in the park at up to 1053 m, it is primarily a low elevation species. The bulk of trees are found beneath 400 m, but cover is disproportionately higher at 300-500 m. This species occurs on all aspects, but is slightly more abundant on south-facing slopes. Resin birch is equally common across all angles of slopes, but it reaches the highest level of cover on moderate slopes (4-12 degrees), and also fairs well on steep slopes (20-28 degrees).

Details are shown in the Plots & Charts found at right. For more on how to interpret these figures, visit Understanding Data Presented.

Resin birch favors mineral soil that is well drained with a deep active layer, preferring higher pH-soils and southern exposure. With its adaptation to reproducing after fire disturbance, this species is correlated to low soil carbon content.

Somewhat poorly drained wet sites to well drained moist sites.