Another Look at Red Alder
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A stand of lichen-covered Alnus rubra, Red alder, is a remarkable sight. Peering through a stand, you can almost see the creatures that artists hide in their paintings of white barked trees and snow. Because alders are such a common tree in the western portion of the Pacific Northwest, they are often thought of as weed trees. I have thought this, too, as I pull the numerous seedlings that volunteer in my ornamental gardens or very close to the fruit trees. However, when I see a mature stand of Red alder, those thoughts quickly disappear. They are important trees for many reasons.
Alders fix nitrogen into the soil--well not exactly. A bacterium called actinomycete invades the alder's roots, where it draws nitrogen from the air and fixes it to the nodules that have formed. If you ever pull up an alder seedling, you can see the orange-red colored nodules all over the roots. In our Northwest soil, this is a great way to get the nitrogen, that our rains wash away, back into the soil. A stand of red alder can provide up to 705 pounds (320 kg) of nitrogen every year! This helps the tree to grow over places like avalanche tracks, flood plains and other disturbed areas, such as where logging has occurred. Alder helps provide the nitrogen for younger conifer seedlings growing up under the protection of their canopy. The alders start to decline after about 50 years, giving way to the next generation of forest trees.
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Epiphytic lichen (lichen that grows on trees) covers most alder tree bark, giving them an appearance similar to a birch tree. Covering the bark, the lichen makes mosaic patterns of white and gray with tinges of light pink. Where the air is free of pollutants, the lichen freely covers the bark. One lichen that frequently grows on alder is called Pencil script (Graphis scripta), a very old species dating back at least 25 million years. It is white with black fruiting bodies that look like small hieroglyphs drawn in pencil. Alder bark is one of its favorite hangouts. Have you ever wondered why you saw barnacles growing on an alder tree? It is not really a barnacle, but a fruiting body of the lichen, Thelotrema lepadinum or Bark barnacle. Without the lichen, the bark would look much like the young tree shown below, only the bark would be brown in color. Where pollution is severe, lichen will die off, making it a good indicator of air quality in an area.
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Red alder grows exclusively west of the Cascades between Alaska and California, except for a few isolated stands in Idaho. You can find Red alder growing in Hawaii, where it was introduced for cultivation. Before settlers came to our Northwest region, alder was restricted to growing alongside streams and wet areas. However, with our expanding population and the logging industry's clear-cutting practices, alder is now quite abundant throughout the region.
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Alder is our most abundant hardwood, used for making fine furniture and cabinets around the world. Alder is still considered the best wood for smoking salmon. Salish and coastal tribes once ate the inner bark of alder, scraping it off in spring and mixing it with oil or drying it in cakes for winter use. Clothes, utensils, dyes and medicines also came from the alder.
The next time you look at a Red alder tree, do not think of it as a weed. Think of all the things it does and you might find it quite fascinating.
USDA zones 6-8
Sunset zones 4-6, 15-17
Debra Teachout-Teashon
Bibliography
Brickell |
Gilkey |
Grant |
Guard |
Hitchcock
Kruckeberg |
Pojar |
Sunset |
WSU
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