Wednesday, 22 October 2014

Alder: a spot of autecology

No. I'm being very pretentious. Autecology is the study of a particular species, and I spent about half an hour wandering around a group of alders. Now if I'd spent a couple of years looking at this species my title could perhaps have been justifiably used.

Any road, I set out on a dry and bright morning, but it was distinctly chilly. My plan had been to visit Stefan Leys Pocket Park (see my blog for 16th October) and gather a few spiders. I am the county spider recorder for the local wildlife trust but now spend so little time studying any arachnids that I am getting embarrassed. My intention was to put things right - or at least make an effort. Unfortunately the grass was wet and, combined with the cold, it made collecting difficult. In the event I only recorded a handful of spiders.

So, on coming across a clump of alders, I decided to look them over carefully. Alders are related to birches and placed with them in the Betulaceae Family. We have only one species, Alnus glutinosa, native to Northamptonshire, where it tends to be confined to riversides and wet woodlands. However, it is frequently planted as an amenity tree and will cope with drier conditions. (Wet woodlands dominated by alder and willow are known as carr.)
Alder, Alnus glutinosa, at Stefan Leys Pocket Park.
Daventry. 22 October, 2014

The tree has rather smooth, grey bark and at one time this bark was used in our county in the tanning industry (although oak bark was used in far greater quantities). Apparently the timber was also put to use for artefacts such as toys and small items of turnery. It rarely makes a very large tree, with 20 metres generally being the upper limit. 

Male catkins of Alder. Stefan Leys Pocket Park.
22 October, 2014

The male catkins are already present and will swell and open up next spring for the pollen to be distributed by wind.

Alder, the female catkins. Stefan Leys Pocket Park,
Daventry. 22 October, 2014

The egg-shaped female catkins are more or less fully ripe and over the next few weeks they will open up and release their seeds. The seeds have air-tight cavities and if they fall into water they will float undamaged through the winter to germinate in the spring. A fungus, Taphrina alni, causes a curious tongue-like growth to protrude from these catkins. Once rare, this fungus now appears to be spreading but I have yet to see it.

These female catkins are rather woody and are sometimes called 'pseudocones'. They will remain on the tree for many months, and the picture opposite shows the pseudocones clinging on from last year.

Of course, this late in the year many of the insects particularly associated with alder such as the Alder Kitten, Furcula bicuspis, and the Alder Moth, Acronicta alni, are not to be seen. This doesn't mean that the trees are devoid of interest.

Phyllonorycter stettinensis. Stefan Leys Pocket Park,
Daventry. 22 October, 2014

This curious  but neat leaf mine is the work of a moth, Phyllonorycter stettinensis. Known as the Small Alder Midget it is widespread across England and Wales, thinning out towards the north and not yet reported from Scotland.

Not at all neat are these very disfiguring galls. In this case a mite, Aceria nalepai, is responsible. It starts tidily enough as small galls in the vein angles but steadily grows to create the mess shown.

Parent Bug, Elasmucha grisea.  Stefan Leys Pocket Park,
Daventry. 22 October, 2014
These leaf miners and galling mites are wholly dependent on alders or their close relatives. The same is largely true of the Parent Bug, Elasmucha grisea. It is to found on birches and alders but more often on the latter (see also blog for 18 October). As with my earlier blog, this bug (for it is a true bug) is assuming its rather drab winter colours.

The famous herbalist Parkinson, writing in 1640, said: "The fresh leaves (of alder) laid on tumours will dissolve them." If only! However, research has shown that the bark contains lupeol and betulin, compounds which some believe may have a role in tumour control.

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