Grey Alder is not very common in Exeter but as it is so similar to Common alder it is often mixed up. There are a small number of grey alder next to Cricklepit Mill and there is a medium sized one at the Cowick Barton playing fields. The key differences are the leaf shape and general structure of the tree. when compared to Common alder. They produce very unusual cone-like fruits that often stay on the tree  throughout the winter. It is a non-native tree species of the UK but is a welcome site in any park or green space.
Grey alder was introduced from Europe in the 1780’s. and is a particularly tough member of the Alder family. Like all members of the Alder family it has the 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. Grey alder can grow on practically any type of soil and with this in mind can be planted in areas with poor soil conditions. It would be a welcome site to see more of these interesting trees planted around industrial estates, recycling centres and similar facilities.
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The underside of the leaves are grey-white in colour
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Grey alder is a small to medium sized deciduous tree growing up to 20m
Grey alder is a conical shaped tree and can reach heights of up to 20m. The leaves are ovate and double serrated and usually up to 10cm in length. The underside is covered in dense hairs and is grey-white in colour. 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 branches are smooth, grey and slightly tomentose to the touch.
The bark is light grey and fairly smooth. The young twigs are sticky to touch. It has a shallow root system and a suckering habit - which can sometimes prove a bit of a nuisance.
During autumn the male cones look like thing green sausages. The pollen is released in late winter / early spring.
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.
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A wide variety of lichen grows on the bark of Grey alder
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During the early winter the male flowers are easy to spot.
Another great thing about Grey 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 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 Grey alder.
OTHER USEFUL LINKS
QUICK FACTS
  • ​The small brown cones, which are the female catkins, stay on the tree all year round
  • Grey Alder is monoecious, which means that both male and female flowers are found on the same tree - but different parts
  •  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 in the past
  • 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
  • The Zuni people use the bark of the tenuifolia subspecies to dye deerskin reddish brown
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 Grey Alder the better. Many thanks!