Saturday, 2 February 2013

Alder Trees

Although there are about 30 species of Alder only one, Alnus glutinosa, is native to Britain. The other species are all confined to temperate regions of the northern hemisphere except for one, Alnus acuminata, found in the Andes of South America. 

Our native Alder is a familiar tree, naturally occurring in wettish habitats such as carr (wet woodland), river sides and damp meadows, although it is quite often planted. More widely planted is the Grey Alder, Alnus incana, of which there are several specimens around Byfield's playing fields, and as I passed them earlier today I saw that they are flowering. The Grey Alder, a Central European species, has a rather smooth greyish trunk whereas that of the Common Alder is dark brown and quite fissured. The two species frequently hybridise.
Male catkins of Grey Alder, Byfield, 2 February, 2013

The previous season's female "cones" on Grey Alder. 
The male flowers are in the form of catkins, not unlike those of Birch or Hazel and, being wind pollinated, can afford to appear early in the year. However, the female flowers are quite a lot different. Technically they are catkins but are in the shape of a cone and, being quite woody, they persist long after the fall of their fruit, so those pictured are from last year. It is as well that pollinating insects are not required since today, despite a bright sun and blue sky, it is bitingly cold. 

Caterpillar of the Alder Moth, Acronicta alni
Alders are important for wildlife. A dozen or so bugs - by which I mean true bugs - occur on the trees and in the Pocket park I have found the rather colourful Pantilus tunicatus on the foliage. Occasionally I also been lucky enough find the unmistakable caterpillar of the Alder Moth, though I have yet to find it in the Byfield area. I will keep looking...

Alder bark was once used in the leather industry as a tanning agent, so in our county it was a tree if some significance.

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