Alnus nepalensis Seeds | Nepalese Alder
LATIN NAME: Alnus nepalensis
COMMON NAME: Nepalese Alder
Plant Profile
Alnus nepalensis is a large alder of the eastern Himalaya, growing up to thirty metres with a straight trunk, dark grey bark and ovate leaves that are pale beneath. It is one of the first trees to colonise landslides and gravel bars, and it is a familiar sight along mountain roads from Nepal through Bhutan into Yunnan and Sichuan.
It is deciduous but briefly so, and the catkins hang in clusters through the winter. The wood is pale, soft and easily worked, and it is used for tea chests, for plywood and for fuel, while the bark yields a red dye used in traditional cloth.
Science & Biotechnology
The alder fixes nitrogen through Frankia, an actinomycete that forms nodules on the roots, which is why it can grow on bare mineral soil where nothing else survives. A landslide colonised by alder accumulates nitrogen and organic matter within a decade, and other species move in behind it.
The seed is tiny and winged, and it is produced in enormous quantities. Germination requires light and bare ground, so the tree depends on disturbance; in a closed forest it rarely regenerates. That dependence explains why alder is common along roads, rivers and cleared slopes and absent from undisturbed stands. The wood is also light enough to be used for packing cases and cheap furniture, and it splits easily when green, so it is dried slowly under cover before milling. The species is also planted to shade cardamom and ginger on terraced hillsides, where its nitrogen and light shade raise the yield of the crop beneath without competing for water.
Uses & Benefits
The wood is used for tea chests, plywood cores, matches and paper pulp, and it is a favoured fuel in the middle hills. In Nepal the tree is planted on terraces and along irrigation channels, where its roots stabilise the soil and its leaf litter improves the field below.
The bark is used for tanning and for a red dye, and the leaf is fed to livestock in the dry season. Alder is also planted in shade systems for cardamom and ginger, since it fixes nitrogen and casts a light shade that suits the crops underneath.
Growing from Seed
Seed should be sown on the surface, since it needs light, on a fine mix kept moist at 20 to 25°C. Germination is rapid, often within two weeks, and the seed keeps well in a dry jar for several years, which makes it easy to hold until a site is ready.
Plant out at one year, at three by three metres for timber or closer for a shelterbelt. The tree tolerates acid, infertile and waterlogged soil but needs sun. It grows fast, three metres in the first three years on a good site, and it is short-lived by tree standards, seldom more than forty years.
Our Take
A pioneer that earns its place by making damaged ground habitable, and the tree to plant first on a landslide, a spoil heap or an eroded bank.
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