Tree to spot in March: Common Alder

Alnus glutinosa

The greens and yellows of early spring are bringing life back to our river valleys. For much of the winter, the flooded fields have reflected little other than the grey of the leaden sky. 

 

 

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Some colour has come from the burgundy-branched alders, whose hues still mark the true river path when the banks themselves have breached. 

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The alder is not a large tree, nor does it live for particularly long, but it has a fondness for water that few other trees can match.

In low quality soil, the alder is a pioneer. Within its root nodules live bacteria, Frankia alni, that feed on sugars produced by the tree. The Frankia begin processes that allow the alder to pass amino acids and nitrogen into the soil, improving fertility for future growth. 

On a steep riverbank, the alder sends out roots from its lower trunk that reach sideways to find footing, preventing the tree from being unseated from below. Those roots that finger out over the water will tuck back beneath themselves, forming a tangle that provides sanctuary for fish and invertebrates. 

Should a limb fall into the water, then it will not necessarily rot. If alder remains submerged, then it will solidify like granite. Man has long utilised this property, building crannogs upon alder in the lochs and loughs of Scotland and Ireland, and using it as a foundation in Amsterdam and Venice.

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In March, the catkins of the alder are maturing from claret to yellow and, once pollinated, the smaller female flowers harden like miniature pine cones. They remain on the tree until long after the rounded leaves have fallen, and snare the lines of anglers who cast for the fish that lurk in the root mass beneath.