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.
The underside of the leaves are grey-white in colour
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.
A wide variety of lichen grows on the bark of Grey alder
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.