Alder Trees in Parklands and Woodlands
The Alder tree is a cousin of the Birch and the Hazel, and like them its flowers and seeds are borne in catkins. It is usually to be found growing by the side of a slow-running stream, over which its slender branches bend gracefully, while its spreading roots cling to the boggy soil at the water's edge. For the Alder does not thrive in dry ground: it is a water-loving tree, and its many tiny roots attract moisture, and suck it up greedily; so that the ground where the Alder grows is often a marshy swamp.
The wood of the Alder was much sought after for buildings which stand in water. In Venice one of the most famous bridges, the Rialto, is built on piles, or great posts of Alder driven deep into the bed of the canal: and old history books tell us that boats were first made of the trunks of the Alder tree. But it is of no use for fences or gate posts, as it decays quickly in dry soil.
If you watch a woodman cutting down an Alder tree you will notice that the chips which fall under his axe are very white; but soon they change colour and become a reddish pink. The hard wood knots which are found in the tree trunk are beautifully streaked and veined and were much prized by furniture makers.
In early spring you should walk to the banks of a stream and look for an Alder tree. Like the Hazel, you will easily know it by its winter catkins, though these are very different from Hazel catkins. Clinging to the boughs you see groups of small brown oval cones, which are quite hard and woody and which snap off easily. These woody cones are the withered seed catkins of last year. As well as these you find bunches of long drooping caterpillars with tightly-shut purple-green scales, which will not unclose till the spring days come. These are the young stamen catkins, and they have taken six months to grow so far. By these you will always know the Alder tree; and it is most interesting to watch day by day how its catkins grow and change.
In spring the tree produces many groups of tiny seed catkins, which are hard and oval and covered with closely-shut green scales. As the days get warmer these cones grow larger and larger, and one day you will find the scales opening as a fir cone does when it is ripe. Underneath each scale are hidden two seeds, and from the top of each seed rise two slender horns. There are no wings to the seed, as in the Birch tree. These seed cones grow fatter and larger all summer, and by autumn their scales, instead of remaining green and soft, have become a dark reddish-brown colour and are hard and woody. In October or November the seed is quite ripe, and is shaken on to the boggy ground below. Then the empty seed catkins become dry and shrivelled, and they remain in groups clinging to the twigs all winter.
But the drooping caterpillars have been growing and changing too. Soon after the seed catkins have unclosed their hard oval balls, so that the sun and light may reach their tiny seeds, these droop¬ing stamen catkins unclose, and their scales take on a deeper shade of reddish purple. Each scale is edged with three points, and each point covers four tiny stamens and four tiny petals. When the fine powder in the yellow stamen heads is ripe, the wind blows it from the dangling tails on to the seed cones which are waiting for it, as without the stamen powder the seeds would never ripen. Soon after this happens the dangling tails fall to the ground.
If you look at an Alder tree in late autumn you will find three kinds of catkins. First, the empty seed catkins with dry woody scales; second, the dangling stamen catkins with the fine stamen dust all blown away; and third, there are tiny little caterpillar catkins with their scales still tightly closed together—these are next year's stamen catkins just begun to form.
The leaves of the Alder are heavy and leathery. They are usually rounded at the tips, but sometimes they are square, as if a piece had been cut off. Each leaf is prettily toothed all round the edge, and the veins, which run from the centre rib to the margin, are very much raised. When the leaves are newly opened, the underside is covered with tufts of soft down, and they are slightly sticky. Sometimes they are tinged with dull purple. These leaves are placed alternately on the stem, and while still in bud each leaf is enclosed in a pair of oval sheaths like small yellow ears. These ears do not fall off when the leaf unfolds, as do the leaf coverings of the Birch and the Beech.
Article Source: Extracts adapted from Trees for Information and Learning - About Alder Trees