This is a hybrid of the Japanese alder (Alnus japonica) and the Caucasian alder (Alnus subcordata). Spaeth’s Alder was first discovered by the botanist Ludwig SpäthintheSpäth Arboretum at the Späth Baumschule (Arboretum) in Berlin. It soon became a popular landscape tree across Europe and has made it's way to several parks in Exeter. The stem of the tree is exceptionally straight and the overall growth habit is narrow which helps to make this a good choice of street tree. On top of that it typically remains a small tree growing to a height of 10 - 15 metres typically. It is tolerant of most soil conditions but dry soils should be avoided. Speath alder is also salt and wind tolerent so is also suitable for coastal regions. Overall - a tough and pretty little tree!
Like most members of the Alder family it is fast growing and fairly short lived. The average lifespan is likely to be no more than 80 years old. Like all members of the Alder family it 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 alder provide to the ground - they should be planted more widely in industrial estates and other areas with general pollution. This tree is tolerant of urban pollution and is suitable as a street tree but should not be planted close to houses due to the shallow spreading roots.
The leaves are alternate, elliptic with serrulate margins and are up to 15cm long
The leaves are shed from November onwards
The leaves are very different when compared to most Alder species and is often mistaken for a cherry tree. The leaves are alternate, elliptic with serrulate margins and are up to 15cm in length so they really stand out. When young they are purple in colour and as they develop they turn into a dark green hue. The underside is a matte green and the topside a glossy green. The leaf arrangment is alternate. The bark is smooth, grey / green with lenticels. It is very late to shed it's leaves so even in December it may still have foilage.
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 December and March which is earlier than most other types of Alder. It 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 4–10cm. The female catkins are red / 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 key feature of this tree is the winter interest of the pretty male catkins as well as the woody / mature female cones.
The tree is very upright and usually no more than 15m in height
Even on these small trees they are often covered with mixed lichen
Another great thing about 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. In the wild 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 this type of alder.
This is a hybrid of the Japanese alder (Alnus japonica) and the Caucasian alder (Alnus subcordata).
It is a deciduous tree which means it sheds it leaves annually
It is a fast growing tree with a straight trunk
It is tolerant of pollution and is suitable as a street tree
The mature female cones stay on the tree all year round
Alder is monoecious, which means that both male and female flowers are found on the same tree - but different parts
The natural habitat of most Alder species 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
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 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
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