[GPI]

Black Alder ... Alnus glutinosa ... Fearnóg
by GPI

I recently discovered that many older Irish people considered it unlucky to pass an alder tree on a journey.
If this were true, then we are all crocked, judging by the frequency with which alder grows throughout Ireland.

. Black Alder leaf, catkin and seed-bearing cone, photo / pic / image.

Scientific classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order: Fagales
Family: Betulaceae
Genus: Alnus

Chromosome number: 2n=28.


Back in black.
Our native alder is the black alder, Alnus glutinosa. A member of the birch family, this deciduous (sheds and renews leaves annually) tree grows up to ½ a metre a year, quickly reaching its maximum height of 20-25 metres. Very quick to establish, and, once established, maddeningly difficult to root out of the ground again, these are two of the reasons that black alder works well as a soil maintainer and erosion reducer to the soils along our river banks.

If you spot a thriving group of Alder trees, you can reliably assume that its roots are sitting in soggy soil, possibly alongside a marsh, stream, river or lake, in situations such as this it is common for the trees to form a dense thicket. Our Alnus glutinosa is very tolerant of waterlogged situations, preferring a heavy soil and damp conditions to all others.
I sometimes jokingly refer to it as the ultimate tree for the wet and windy west. Yes, windy, that’s right, as maritime exposure is no problem to the black alder. It can be grown as a windbreak or a hedge, quickly providing sheltered conditions, allowing further and tenderer plantings to become established within its cover.

The wind through the catkins.
The wind absorbing foliage of the alder, held amongst ascending branches, appears in April, with leaves that are broad, circular and irregularly margined. Their time on the tree lasts late into autumn, when they eventually shed, they do so without the fiery colour display we come to expect from other deciduous (sheds and renews leaves annually) trees.

The flowers of the alder known as catkins, open in March to await pollination by the passing breezes. These catkins pollinate the female flowers, which grow as small green rounded cones, in clusters of four at the end of twigs. When they ripen, usually by October, they turn woody and release small flat reddish-brown seeds.

The then seedless cones remain as an interesting and decorative winter feature, hanging onto on the tree until the following spring. Alders are, to my knowledge, the only deciduous (sheds and renews leaves annually) trees utilising tiny cones such as this to bear seeds.

For insects, moss and nitrogen, just add Alder.
An established Alder tree within your garden offers refuge for up to 90 species of insects, not to mention the many varieties of moss and lichen, which will aim to clothe moist area alders. Grass will even be allowed to grow in tandem with the alder, as unlike other trees it does not siphon nitrogen away from grass around it.

In fact, it actually makes nitrogen available to grass and other plants growing nearby, through the amazing nitrogen-fixing bacteria growing in its root nodules. These nodules add fertility to the soil wherever the alder grows, allowing the tree to tolerate poor soils, such as the clays found in many reclaimed lands.

In Ballyseedy Wood, near Tralee, you will have a good opportunity to see a native Irish alder which has reached more than 23 metres in height, with a trunk which is more than three metres round.
Click for map if you wish to visit and view.

Other interesting Black Alder facts.
During archaeological excavations at Dublin’s Wood Quay, native alder wood was found in the form of posts and other turned items.

Alder is extremely prone to tearing if cut or machined with unsharpened tools. Alder is easily finished, sanded, and takes staining well.

Sawn alder wood is known to be susceptible to woodworm attack.

Alder is also susceptible to a form of Phytophthora disease (Alder Phytophthora).
Trees affected develop lesions on the bark of the stem, along with the production of a tarry or rusty exudate. The trees foliage may become small, sparse and yellowed. Trees affected normally die quite rapidly.
To avoid introduction of the disease, seed sources and alder plants of unknown or dubious origin should be avoided.


Chart shows approximate distribution of the native tree within Ireland, each dot is a 10km square in which the species grows.

. Black Alder growing in an Irish bog, photo / pic / image.


Video. See a huge single stemmed alder in the Lake district.

Any queries or comments on our Native Irish Black Alder, please post below.


Back to native Irish trees.

Black Alder Images courtesy
Paul Wray, Iowa State University, United States.
Piero Amorati, ICCroce - Casalecchio di Reno, Italy
www.forestryimages.org
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