August 31, 2021

Thinleaf or Mountain Alder A Mighty Nitrogen Fixer

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Thinleaf or Mountain Alder A Mighty Nitrogen Fixer Photo © Dr. Mark S. Brunell

Thinleaf or mountain alder is a common large canyon shrub or tree, of the birch family,  widespread on the banks of streams and on hillsides in the foothills and montain forests to 10,000 feet elevation, and along stream beds. A truly magnificant benefit of alder is their ability to move nitrogen from the atmosphere into the soil. This process is called nitorgen fixing. Nitrogen, the most abundant element in our atmosphere, is crucial to all life on earth. Nitrogen is found in soils and plants, in the water we drink, and in the air we all share and breathe. 

A small amount of nitrogen can be natually fixed when lightning form above strikes and provides the energy needed for N2 compound to react with oxygen, producing nitrogen oxide. This nitrogen formula then enter soils through rain or snow. Most nitrogen fixation occurs naturally, in the soil, by bacteria. Some bacteria attach to plant roots and have a symbiotic relationship with the plant. The bacteria get energy through photosynthesis and, in return, they fix nitrogen into a form the plant needs to build healhy tissue. Alder tolerates a wide variety of soil textures and pH but is most commonly grows in moist soils but is well-adapted to cold, "heavy" soils, thinleaf alder is an indicator of productive sites and common in many riparian shrublands. 

Leaves alternate; simple; ovate-oblong; 2" to 4" long; deciduous; sometimes slightly lobed; doubly serrate; thin; glabrous; dark green above, pale yellow-green beneath; petiole short. Alder wood in general is light and soft, white to pinkish color, and unnoticeable heartwood; often used in furniture, veneer, and carvings. Beacuse it is evenly textured wood that has a strong reputation for being an excellent wood for machining, Alder wood can be nailed without splitting and longlasting hardness. Its grain is better than cherry and makes for a nice finish. 

The next time you are outside see if you can identify an alder, take time and thank it for it's good nitrogen fixing job!