Alnus glutinosa - Schwarzerle

Common name: Alder, Common Alder, Black Alder, European Alder

Scientific name: Alnus glutinosa

Family: Betulaceae

Origin: Native to Switzerland
 

Summary: Swamp-dweller, water-lover. The wood of this tough tree doesn’t rot when waterlogged, instead turning stronger and harder. Conical in shape, mature trees can reach a height of around 28m and live to approximately 60 years. The bark is dark and fissured and is often covered in lichen. Twigs have a light brown, spotted stem which turns red towards the top. Young twigs are sticky to touch.

Leaves: The purple or grey leaf buds form on long stems and the 3–9 cm long, dark green leaves are racquet-shaped and leathery, with serrated edges. The leaf tip is never pointed and is often indented.

Flowers: Flowers are on catkins which appear between February and April. Alder is monoecious, which means that both male and female flowers are found on the same tree. Male catkins are pendulous, measuring 2–6 cm, and turn yellow. Female catkins are green and oval-shaped and are grouped in numbers of three to eight on each stalk.

Fruits: Once pollinated by wind, the female catkins gradually become woody and appear as tiny, cone-like fruits in winter. They open up to release their seeds, which are dispersed by wind and water

Value to wildlife: Alder is the food plant for the caterpillars of several moths including the alder kitten, pebble hook-tip, the autumnal and the blue-bordered carpet moth. Catkins provide an early source of nectar and pollen for bees, and the seeds are eaten by the siskin, redpoll and goldfinch. The wet conditions found in alder woodland are ideal for a number of mosses, lichens and fungi, along with the small pearl-bordered fritillary and chequered skipper butterflies, and some species of crane fly. Alder roots make the perfect nest sites for otters.

Uses of alder: Soft and porous, alder wood is only durable if kept wet, and its value to humans is down to its ability to withstand rotting in water. Historically, it has been used in the construction of boats, sluice gates and water pipes. These days, alder wood is used to make timber veneers, pulp and plywood.

It is thought that the female woodworm lays eggs in alder in preference to other wood. Traditionally, alder branches were cut and placed in cupboards to deter woodworm from laying eggs in the cupboard timber.

Alder coppices well and the wood makes excellent charcoal and gunpowder. The roots have nitrogen-fixing nodules, conditioning the soil and improving soil fertility on former industrial wasteland and brownfield sites. Alders are also used in flood mitigation.

Alder used to be the preferred wood to make clogs, and it was said that a few alder leaves placed in the shoes before a long journey would cool the feet and prevent swelling.

Did you know?: Much of Venice is built on alder piles, thanks to the durability of its timber in water.

Text courtesy of the Woodland Trust