I've come across it as being included in what's known as 'riparian habit' (interface between land and fresh water), I was told by an old forester that they have a long tap root that can be deeper then the tree is tall. looked up online for verification and found this info... some of it duplicated what's been poted already but enough of interest to repeat i think. interesting bit on not splitting when nailed, astringent qualities
Alder - Alnus glutinosa
Alder cones
Irish name - Fearnóg
Ulster Scots name - Allertree
Birch family - Betulaceae
Characteristics
* Alder usually grows to a height of 15m but occasionally reaches 30m, and it lives up to 150 years.
* When young, these trees have strong single trunks and are conical in outline, but become broadheaded with age.
* Young trees grow quickly when in suitable conditions and are capable of putting on as much as 0.5 metre’s growth a year, for the first 30-40 years.
* Roots sometimes grow near the base of the stems and help support the trees in unstable ground. Such new growth is particularly common on coppiced plants.
* Alder trees put more nitrogen in the soil than they use, so they build up soil fertility.
* An established alder has a deep-probing tap root, about 1.5m long, which enables the tree to survive falling water levels during drought.
Season
* Alder produces yellow catkins early in February and March.
Preferred Environment
* Alder seed is generally distributed by wind and water. The seedlings survive water logging, but require high levels of light, humidity and oxygen, which restrict natural establishment to river banks and mud. This means that alder is found frequently along streamside’s and in marshland where it can become dominant in areas which are not permanently flooded.
* It thrives best in moist loam with high humus content. It is, however, tolerant of most soils, except chalk, and is able to withstand prolonged root submergence. For this reason alder is often successful on reclaimed land.
Wildlife Associations
* There are 90 associated insect species identified with alder.
Uses
* When dry, alder wood is water-resistant, and does not split when nailed. It is used for broom and tool handles.
* Alder is a hard but easily carved yellow timber that is still used occasionally as the traditional material for the soles of clogs or wooden shoes.
* The bark and leaves contain tannin and have astringent properties. Used in folk medicine to treat chill.
* When submerged in water it becomes as hard as stone. For these reason much of Venice is built on piles made from alder trunks.
