Common Name: Japanese Alder

General Information

Alnus japonica is a shrub or tree with a dense crown; it usually grows 3 - 10 metres tall, exceptionally to 20 metres[]. The bole can be up to 70cm in diameter; it is usually short, especially in trees grown in the open where the lower branches are generally retained[, ]. Deciduous in most of its range, the tree has adopted an evergreen habit where it is grown in the Philippines[].
The tree is a popular fuel, harvested from the wild for local use. It also has medicinal properties and is a source of wood and dyes. It is grown in reforestation projects, to provide shade in plantations and to stabilize and recondition the soil. It is sometimes grown as an ornamental[].
This species has a fairly wide distribution, and there are no known threats impacting ts survival. The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2013)[].

Known Hazards

None known

Botanical References

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Range

E. Asia - Russian Far East, China, Japan, Korea, Taiwan.

Habitat

Wet soils along streams and in swamps and also on exposed soils. In Japan, it occurs in marsh or swamp forest with a high water table and soil conditions tending to be anaerobic with high clay and organic matter contents[].

Properties

Conservation Status	Least Concern
Medicinal Rating
Other Uses Rating
Habit	Deciduous Tree
Height	8.00 m
Growth Rate	Fast
Pollinators	Wind
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Alnus japonica is a plant mainly of temperate regions where it can experience very cold winters. It does also extend south to Taiwan where it enjoys a subtropical climate and is also cultivated in the Philippines, usually at higher elevations.
Grows best in a sunny position, but is shade tolerant[]. Prefers a heavy soil and a damp situation, but it succeeds in ordinary garden soil[]. Grows well in heavy clay soils[]. It does not require fertile soil, but prefers permeable soils and should not be planted in compact soils[]. Thrives in drier soils than many members of this genus[]. Tolerates very infertile sites[]. Tolerant of inundation of the soil, under such conditions the tree retains its leaves and can almost maintain its growth rate by forming adventitious roots[].
A fast-growing tree - on fertile sites, poles and firewood can be harvested after 5 years, small-diameter timber can be harvested in less than 10 years[].
The tree responds well to coppicing[].
This species has a symbiotic relationship with certain soil micro-organisms, these form nodules on the roots of the plants and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[].

Edible Uses

None known

Medicinal

The stembark and leaves are used in the treatment of cancer, gastric disorders, hepatitis and fatty liver[]. In oriental traditional medicine the stems and stem-bark are used as remedies for fever, haemorrhages, diarrhoea, and alcoholism[]

Various species of alder, including this species, seem to contain antitumour compounds[].
The stems and stem-bark contain various medicinally active compounds that have cytotoxic properties and are of potential use in the treatment of cancer[].
The plant has also been shown to be hepatoprotective; to have antioxidant activities; and antiviral activity against the
influenza virus[].

Agroforestry Uses:

A pioneer species, succeeding in full sun and also fixing atmospheric nitrogen, the tree can be grown in reforestation projects[, ]. It has been planted in reforestation projects on areas of land used in mining and alo on mine waste tips[, ].
The tree is fast-growing and has an extensive lateral root system. It is planted to stabilize the soil on slopes and areas where there have been landslides[, ].
The tree is grown to provide shade in coffee plantations and as a nurse tree in Pinus kesiya plantations in the Philippines[, ]. It is also grown there to act as living posts, supporting wires that are used for growing chayote (Sechium edule)[].
The tree has been found to be suitable for use as bed logs for growing shiitake mushroom (Cortinellus shiitake)[].

Other Uses

A dye is obtained from the bark[, ]. No more details are given.

The pale brown wood is medium to fine textured, close grained, moderately soft, light in weight. It seasons without excessive warping or splitting, but shrinkage figures are high. It is easy to saw and finish by hand or machine, with only slight blunting effects on tools. Planing and boring give good results while mortising and turning results are only fair with some picking up of grain. It is used for turnery[, ]. The wood is suitable for making furniture, tools, packaging[].
The wood is used for fuel and to make a good quality charcoal[, , ]. Although the energy value of the wood is relatively low, it dries rapidly and burns easily and so is a popular fuel[].

Propagation

Seed - best sown in a cold frame as soon as it is ripe and only just covered[]. Spring sown seed should also germinate successfully so long as it is not covered[, ]. The seed should germinate in the spring as the weather warms up. When large enough to handle, prick the seedlings out into individual pots. If growth is sufficient, it is possible to plant them out into their permanent positions in the summer, otherwise keep them in pots outdoors and plant them out in the spring.
If you have sufficient quantity of seed, it can be sown thinly in an outdoor seed bed in the spring[]. The seedlings can either be planted out into their permanent positions in the autumn/winter, or they can be allowed to grow on in the seed bed for a further season before planting them.
Cuttings of mature wood, taken as soon as the leaves fall in autumn, outdoors in sandy soil.