Buch.-Ham.
Description
Betula alnoides Buch.-Ham. ex D.Don is a tall, fast-growing birch of the warm-temperate and subtropical mountains of southern and eastern Asia. Its distribution covers Nepal, northeast India, Bhutan, southern China, Myanmar, Thailand, Laos and Vietnam, with cultivated and trial occurrences recorded elsewhere. It is a light-demanding, often pioneering tree of moist broad-leaved and mixed montane forests, ravines and disturbed slopes, typically between about 1,000 and 2,800 m. The tree photographed at Yatong-La in Bhutan at 2,800 m in May sits near the upper edge of this band, within the humid mid-montane forest belt where the species frequently colonises gaps and forest margins.
The tree is deciduous and may reach 20–30 m, with smooth, brownish to reddish bark that exfoliates in thin papery sheets and bears conspicuous horizontal lenticels. The leaves are alternate, ovate-lanceolate with a long acuminate apex, doubly serrate margins and several pairs of straight lateral veins. As in all birches the plant is monoecious: the pendulous male catkins elongate at anthesis, while the smaller female catkins develop into slender, drooping, cylindrical infructescences that disintegrate to release small two-winged samaras adapted for wind dispersal.
Betula alnoides is the most important commercial birch of subtropical Asia, valued for its high-quality, reddish, fine-grained timber and increasingly grown in plantations and agroforestry across southern China and adjacent countries. Its rapid early growth and ability to fix sites make it useful in reforestation of degraded montane land. The species belongs to a group of subtropical birches distinct from the better-known temperate white birches, and although widely exploited it remains common and is not regarded as threatened.
Author: Buch.-Ham. · Sources: POWO (Kew), GBIF, Flora of China Vol. 4, Flora of Bhutan Vol. 1, Ashburner & McAllister: The Genus Betula (2013)