Alnus incana, also known as the European Speckled Alder, Gray Alder, Grey Alder, Hoary Alder, and Mountain Alder, is a deciduous tree that can grow up to 60 ft. It is an excellent pioneer species for re-establishing woodlands on disused farmland and difficult sites due to its fast growth rate. The tree provides sheltered conditions for permanent woodland trees to become established. Additionally, bacteria on the roots fix atmospheric nitrogen, making it available to other plants growing nearby. The tree has an extensive root system and can be planted to control banks from erosion. Alder trees have a heavy leaf canopy that helps to build up the humus content of the soil. However, Alder seedlings do not compete well in shady woodland conditions and gradually die out as other trees become established. Grey Alder has a wide range across the cooler parts of the Northern Hemisphere and is a light-demanding, fast-growing tree that can grow well on poorer soils. It is sometimes used for afforestation on non-fertile soils, which it enriches by means of nitrogen-fixing bacteria in its root nodules. The tree is cultivated in parks and gardens.