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.
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.
Wood - 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 also makes a good charcoal.
Because they tolerate very poor soils and also produce nitrogen nodules on their roots, alders are suitable for use in land reclamation schemes. The plants can be used as a source of biomass.
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 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.
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.
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.
Seed requires 6 weeks cold stratification.
Only lightly cover the sown seed. 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.