Common name: Nepal alder

Native to the Himalayan foothills of northern India and adjacent elevated forests of northern Myanmar (Burma), Thailand and Vietnam, this fast-growing forest tree can be up to 30 m (100 ft) tall. However, it is more typically 15 to 20 m (50 to 65 ft) tall on open sites.

It develops a slim, straight trunk gently widening toward the base, with silver-grey bark and a wide-spreading, irregular-shaped crown. The leaves are oval with wavy margins and are deciduous, detaching and falling during the dry season to conserve water. They are replaced by new leaves emerging in the rainy or monsoon season, coinciding with summer in its native range.

The flowers are male or female on the same tree and bloom in the spring. Male flowers are yellow, small but arranged closely in showy tail-like clusters hanging from the branches. Female flowers are small and insignificant and are in clusters that resemble small, green pine cones. 

Use

It is mostly planted on steeply sloped land in forestry systems to minimise soil erosion and provide other environmental services. These include watershed protection, crop shading and soil improvement through nitrogen-fixing, especially in tropical highland areas. It is the primary shade tree in Cardamom (Elettaria cardamomum) plantations in India.

The wood is soft, non-durable and lightweight, with a density of around 350 kilograms per cubic meter and with low natural resistance to rot, decay and termite attack, making it unfit for most types of construction. Its use is limited to the manufacture of light wooden articles and firewood, for which it is not ideally suited because of its low caloric value, resulting in it burning quickly to ash.

Climate

Grows naturally in sub-humid to humid subtropical and tropical high-elevation climates, generally areas with annual lows of 4 to 17°C, annual highs of 15 to 28°C, annual rainfall of 1000 to 2500 mm and a dry season of 5 months or less.

Although also growing naturally in areas with less than 1000 mm annual rainfall and a pronounced dry season of up to 8 months, the trees usually grow alongside a stream or other watercourse, where the roots have permanent access to water.

Growing

New plants are usually started from seed without pre-treatment and by transplanting bare-rooted, seedling plants. It performs best on free-draining clay and loam soils of a slightly acid to alkaline nature, generally with a pH of 6.0 to 8.0 and on sites with full to partial sun exposure.

Problem features

It is listed as a weed in a least one reference publication, but there does not appear to be any records of it as a serious weed. The Hawaii Pacific Weed Risk Assessment project (HPWRA) assessed it as a low weed risk species for Hawaii.