Common Name: Alder

General Information

Alnus glutinosa is a deciduous tree usually growing 20 - 30 metres tall, occasionally reaching up to 35 metres[].
The tree is harvested from the wild for use as a medicine and as a source of wood, dyes etc. It is often grown as an ornamental, many cultivars have been developed including dwarf forms and forms with incised leaves[].
This species has a wide distribution across Europe and into North Africa. Although population size has not been quantified, it is not believed to approach threshold values for a threatened category. Due to the scattered nature of subpopulations, potential future threats exist, but these are not considered significant at present. The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2013)[].
The tree has escaped from cultivation and become widely naturalized throughout the temperate Northeast of North America, occasionally becoming a weedy pest[]. This plant may become weedy or invasive in some regions or habitats and may displace desirable vegetation if not properly managed[].

Known Hazards

None known

Botanical References

, ,

Range

Europe - Norway to Spain, east through Russia to western Siberia, through Greece to Turkey and Kazakhstan; N. Africa - Morocco to Libya.

Habitat

Wet ground in woods, near lakes and along the sides of streams, often formng pure woods n succession to marsh or fen[].

Properties

Weed Potential	Yes
Conservation Status	Least Concern
Medicinal Rating
Other Uses Rating
Habit	Deciduous Tree
Height	25.00 m
Growth Rate	Fast
Pollinators	Wind
Cultivation Status	Wild

Cultivation Details

Alnus glutinosa favours a moderate to cold climate and prefers damp or wet soils. It is estimated to tolerate an annual precipitation of 400 - 2,000mm, an annual average temperature of 8 - 14°c[].
Prefers a heavy soil and a damp situation[, ], tolerating prolonged submergence of its roots and periods with standing water to 30cm deep[, ]. Plants can also grow quickly in much drier sites, though they will usually not live for so long in such a position. Alders grow well in heavy clay soils[, ], they also tolerate lime and very infertile sites[]. Tolerates a wide range of soils but prefers a pH above 6[]. Very tolerant of maritime exposure[, , ]. Prefers a pH n the range 6 - 8[].
The leaves often remain green on the tree until late autumn, or even later on young seedlings.
The seeds contain a margin of air-filled tissue and are capable of floating in water for 30 days before becoming waterlogged[]. This enables distribution of the seed by water.
The alder has a very rapid early growth[], specimens 5 years old from seed were 4 metres tall even though growing in a very windy site in Cornwall[].
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[, ]. Nitrogen-fixation by trees up to 8 years old has been put at 125 kg/ha/yr., for 20 years at 56 - 130 kg/ha/yr.[].
Trees often produce adventitious roots from near the base of the stem and these give additional support in unstable soils[].
Trees are very tolerant of cutting and were at one time much coppiced for their wood which had a variety of uses[, ].
Alders are an important food plant for the caterpillars of many butterfly and moth species[] and also for small birds in winter[].There are 90 insect species associated with this tree[].
The cones open gradually and release seed throughout the winter, they are a dependable source of food for seed-eating birds such as pine siskins and goldfinches[].
There are some named varieties, selected for their ornamental value[]

Edible Uses

None known

Medicinal

The bark is alterative, astringent, cathartic, febrifuge and tonic[, , , , ]. The fresh bark will cause vomiting, so use dried bark for all but emetic purposes[]. A decoction of the dried bark is used to bathe swellings and inflammations, especially of the mouth and throat[, , , ]. The powdered bark and the leaves have been used as an internal astringent and tonic, whilst the bark has also been used as an internal and external haemostatic against haemorrhage[]. The dried bark of young twigs are used, or the inner bark of branches 2 - 3 years old[]. It is harvested in the spring and dried for later use[].
Boiling the inner bark in vinegar produces a useful wash to treat lice and a range of skin problems such as scabies and scabs[]. The liquid can also be used as a toothwash[].
The leaves are astringent, galactogogue and vermifuge[]. They are used to help reduce breast engorgement in nursing mothers[]. A decoction of the leaves is used in folk remedies for treating cancer of the breast, duodenum, oesophagus, face, pylorus, pancreas, rectum, throat, tongue, and uterus[]. The leaves are harvested in the summer and used fresh[].

Agroforestry Uses:

Tolerant of clipping and maritime exposure, the alder can be grown in a windbreak or a hedge[]. The trees are very quick to establish[] and will grow at a rate of 1 metre or more per year when young[].
This is an excellent pioneer species for re-establishing woodlands on disused farmland, difficult sites etc. Its fast rate of growth means that it quickly provides sheltered conditions to allow more permanent woodland trees to become established. In addition, bacteria on the roots fix atmospheric nitrogen - whilst this enables the tree to grow well in quite poor soils it also makes some of this nitrogen available to other plants growing nearby. Alder trees also have a heavy leaf canopy and when the leaves fall in the autumn they help to build up the humus content of the soil. Alder seedlings do not compete well in shady woodland conditions and so this species gradually dies out as the other trees become established[].
Because they tolerate very poor soils and also produce nitrogen nodules on their roots, alders are suitable for use in land reclamation schemes. It has been used extensively to control erosion and improve the soil on recently cleared or unstable substrates, such as sand dunes and mine spoils. Its roots break up wet compacted soil where free oxygen is limited and with a bacteria-like organism on the roots it can convert atmospheric nitrogen into a usable form[].

Other Uses

The plants can be used as a source of biomass[]. According to the phytomass files, annual productivity is estimated at 6 to 9 tonnes per hectare. The tree has yielded 11.8 tonnes per hectare per annum on pulverized fuel ash and annual productivity has been estimated at 8.66 tonnes per hectare, with 5.87 tonnes in wood, bark, and branches, 2.79 tonnes in foliage[]. Alder has been recommended for consideration for firewood plantations in Tropical highlands where unseasonable cold might destroy the red alder[].

The powdered bark has been used as an ingredient of toothpastes[]. Sticks of the bark have been chewed as tooth cleaners[].

The bark and the fruits contain up to 20% tannin[, , ], but they also contain so much dyestuff (imparting a dark red shade) that this limits their usefulness[, ]. The leaves are also a good source of tannin[].
An ink and a tawny-red dye are obtained from the bark[, , , ].
A green dye is obtained from the catkins[, , ].
A pinkish-fawn dye is obtained from the fresh green wood[, , ].
A yellow dye is obtained from the bark and young shoots[, , ].
A cinnamon dye is obtained from the shoots if they are harvested in March[]. If they are dried and powdered then the colour will be a tawny shade[].

The leaves are clammy and, if spread in a room, are said to catch fleas and flies on their glutinous surface[, ].

The wood is light red, yellowing upon exposure to moisture. It is very durable in water, elastic, soft, fairly light, easily worked, easily split. It is often used for situations where it has to remain underwater and is also used for furniture, pencils, bowls, woodcuts, clogs etc. It is much valued by cabinet makers[, , , , , , , , , ].
The wood is used for fuel and also makes a good charcoal[, , ].

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. There are about 700,000 - 750,000 seeds per kilo, but on average only about 20 - 25,000 plantable seedlings are produced[]. Seeds can remain viable for at least 12 months after floating in water[]. Seeds germinate as well under continuous darkness as with normal day lengths. Air-dried seeds stored at 1 - 2°C retained their viability for two years. Seeds can however be sown immediately as soon as ripe[].
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.