Common Alder is fairly common in Exeter and is more often a shrub rather than a tree. There are many Common alder shrubs along the banks of the river Exe. There are also two small trees between the back of the old bus station and Sidwell street. They produce very unusual cone-like fruits that often stay on the tree throughout the winter. As a native tree species it is important we keep the ones we have and continue to plant more.
If you are lucky enough to come across a tree rather than the shrub form they are usually conical in shape. Common alder is actually quite short lived and can live to up to 170 years but is typically much less. It does best in moist areas so anywhere near streams and rivers, although it will still tolerate drier soils. Common alder has a very special ability - to fix Nitrogen in the soil. It has a symbiotic relationship with a friendly bacterium called Frankia alni. This friendly partnership allows the airborne Nitrogen that is trapped underground to be converted into soil based nitrates. Similar to Silver Birch - it is a pioneer species so will be the first to colonise open / barren land. Due to the huge benefits that Common alder provide to the ground - they should be planted more widely in industrial estates and other areas with general pollution. They are massively overlooked by councils across the UK as they are one of the few native tree species that can grow on extremely poor soils.
The leaves are 3–9cm long and dark green in colour. They are racquet-shaped and leathery, with serrated edges. The leaf buds are purple or grey and form on long stems and can be quite sticky. The leaf tip is never pointed and is often indented. The bark is dark and fissured and is often covered in lichen. The twigs have a light brown spotted stem which turns red towards the top. The young twigs are sticky to touch.
During pollen release the male flowers are lovely shades of yellow, red and brown
The fruit is a woody cone like structure and the seeds are dispersed by wind and water
The 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 but different parts. The male catkins are yellow and pendulous, measuring 2–6cm. The female catkins are green and oval-shaped and are grouped in numbers of three to eight on each stalk. Once pollinated by the wind, the female catkins gradually become woody and appear as tiny, cone-like fruits in winter. They open up to release seeds, which are dispersed by wind and water.
Another great thing about Common alder is the roots can help against flooding as they can soak up a lot of water as well as helping to stabilise the structure of riverbeds and other bodies of water. Interestingly the wood of Common alder does not rot under water. This allows all sorts of creatures to make homes within the roots such as otters and other water dwelling mammals. As it is often by water it also provides shelter for smaller fish. Aquatic insects such as water beetles, caddis flies and stoneflies feed off the leaves that fall into the water. Small birds such as Goldfinch eat the seeds and many insects and spider species are associated with Common alder.
OTHER USEFUL LINKS
- The small brown cones, which are the female catkins, stay on the tree all year round
- Common Alder is monoecious, which means that both male and female flowers are found on the same tree - but different parts
- Its natural habitat is moist ground near rivers, ponds and lakes and it thrives in damp, cool areas such as marshes, wet woodland and streams where its roots help to prevent soil erosion
- It grows well from seed and will quickly colonise bare ground
- Because of its association with the nitrogen-fixing bacterium Frankia alni, it can grow in nutrient-poor soils where few other trees thrive
- 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
- Alder roots make good nest sites for otters
- The green dye from the flowers was used to colour and camouflage the clothes of outlaws like Robin Hood
- An ink and a tawny-red dye are obtained from the bark
- 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
- When cut, the pale wood turns a deep orange, giving the impression of bleeding. As such, many people feared Alder trees and the Irish thought it was unlucky to pass one on a journey
- The wood has been used in the construction of boats, sluice gates and water pipes, and much of Venice is built on Alder piles
- Currently Alder wood is used to make timber veneers, pulp and plywood
- The roots have nitrogen-fixing nodules which make it an excellent soil conditioner
- They are also used in flood mitigation
- The trees are very quick to establish and will grow at a rate of 1 metre or more per year when young
- In the past the powdered bark has been used as an ingredient of toothpastes
- The bark and the fruits contain up to 20% tannin
- The wood also makes a good charcoal
- Venice is built on foundations of alder trunks
- Alder wood is still used today to make the bodies of top end Fender electric guitars such as the Stratocaster
- Alder cones have been used for many years by European breeders of soft water fish as a natural way to protect eggs from fungus and bacteria. See a YouTube video for more details
PLEASE LEAF ME ANY FEEDBACK / COMMENTS
If there is anything out of place or wrong please contact me. Equally if there is anything you wish to add please let me know. The more information we have about Common Alder the better. Many thanks!