March 2024

Common alder

This is a native tree that thrives in damp conditions; a state of affairs not unknown at the Rec, which those of you familiar with the park will attest to!! It’s commonly found on riverbanks, in marshes and wet woodland; the latter being referred to as alder carr. But its deep roots will allow it to grow in drier conditions, and it can also cope with nutrient poor soils. This is because there are nodules attached to the roots containing nitrogen fixing bacteria which help to nourish the tree.

The alder is particularly easy to identify during the winter. Its twigs are purple giving the extremities of the tree a distinctive purplish tinge. This is especially obvious when caught in the low winter sunlight. Stripped of all its leaf cover, you can also see the numerous clusters of pendulous male catkins (similarly purply) and small cone like structures, which are the remnants of last year’s female catkins. If you see a deciduous tree with what appears to be small pine cones, it is almost certainly an alder.

The alder flowers early in the year, before the tree breaks into leaf. The male catkins that started to form in the previous year are initially upright, but as they grow, they begin to hang downwards. Then, in February or March they open out to reveal and release their bright yellow pollen. If you handle a mature male catkin, the pollen will leave a yellow residue on your skin.

The reddish, cone-shaped female flowers also occur on the same tree and stand upright at the end of the twigs. They are wind pollinated by the surrounding male catkins and go on to develop into small green cones. The cones ripen and open out in the autumn to release the seeds. The ‘spent’ cone remains on the tree until the following year and these are the ones that are visible during the winter. The seeds are adapted to disperse in water. They are flat and waxy with 2 wings that contain air bubbles, enabling them to float and in the right conditions, spread more widely.

The photographs  show twigs and catkins that were brought down by the gales, and found beneath the alders at the Rec (in the dog walking area). They show all the features described above, including one or two leaf buds. Again, the leaf of the alder is quite distinctive. It has been described as being racquet shaped and leathery with serrated edges and an indented tip. The bark darkens as the tree ages and is deeply fissured (see top photo). Horizontal lenticels are often apparent and these are specialised pores that facilitate gaseous exchange from the atmosphere to the tissues of the tree

When an alder is pruned or felled, it ‘bleeds’ red sap giving the wood a startling bright orangey-red colour. Because the wood doesn’t rot in water it has been used for things such as sluice gates, boats and piles; most notably in Venice. It was also commonly used to tan leather, produce gunpowder and manufacture clogs. It has considerable wildlife value, helping to stabilise riverbanks and playing host to many animal species, including a number of moths.

Be sure to look out for this winter beauty which unlike a certain celebrity chef, is definitely not averse to a soggy bottom!!!

Words and photos: Denise Long