How to Identify Alnus rubra in the Winter
One of the best parts of observing trees is watching them perform their sexual dances each year. Every tree species is different, and starting in late winter they all employ their tricks in order to be fertilized and make seeds for the next generation of trees. Alnus rubra, known commonly as the “red alder,” is a wonderful example of showy sexual reproduction.
Each year in the late winter, male and female catkins hang off the alder’s branches, much like how they do on trees in the Corylus genus. The alder’s male catkins are long and skinny, and they’re covered in pollen-dusted anthers. Alnus differs from Corylus in that Alnus trees have female catkins that look like mini cones with many stigmas, rather than a single stigma on a bud. Out of the female catkins the red stigmas patiently await pollen to fertilize themselves with.
Find this tree in temperate forests, riversides, and swampy areas from California to Alaska in the Western United States. We humans have been using this tree for decades in woodworking, indigenous medicine, and basket weaving. In nature, it is a favorable tree for use in restoration projects, erosion control, and reforesting initiatives.
Uses
Alnus rubra gets a bad rap in the urban landscape, but it is a stellar tree in the right spot. This Pacific Northwest native is fast growing to heights between 40 to 80 feet, and so can be a hazard when planted next to buildings in stormy areas. It will also spread viable seeds in wet areas that have bare soil or that have been recently disturbed.
Do not be alarmed though, as there are many other places this alder should go. The beauty of this wet lover lies in its tolerance of being flooded. It can sit in brackish water for a time, making it an excellent option for floodplain and swampy areas.
In areas with clay soil, you can plant this tree as a restorative force. A. rubra fixes nitrogen at its roots, all thanks to microorganisms that grow in harmony with the tree. These tiny little bacteria fix nutrients by pulling gaseous nitrogen from the air and converting it into nitrates that plants can absorb with their roots.
Any wasteland, dumpsite, or deserted lot is desirable for Alnus rubra. It loves excess nutrients and moisture, and it can grow in harmony with conifers. Eventually, the conifers may crowd out the alder, however, the partnership is viable in its early stages. The conifers will thrive in the long run because of the nitrogen pulled into the soil by the alders, and the alders will slowly add nutrient-rich leaf litter into the soil while they live.
Identification
Use these pictures and descriptions to identify Alnus rubra in the winter and early spring, before the tree’s buds open up into leaves.
Buds
The buds are reddish-maroon in color, and they look like they are separated into two. One half slightly extends over the other, giving the buds a pointy look.
Flowers
Alnus rubra is monoecious. This means the tree has separate male and female flowers on the same tree. The male flowers are long, dangling catkins covered in male anthers that are coated in pollen. The female catkin looks like a mini cone when observed up close. Red sticky stigmas extend out of the female flowers. When pollen falls from the male catkins onto the female ones, the female catkins become pollinated and swell into cones.
Cones
Alder cones are small and closely resemble birch cones (Betula). Each cone is layered, and the seeds extend out of the folds. These cones may hold onto the branches well into winter and early spring.
Bark
A. rubra has gray bark mottled with white. The white color is lichens growing on the tree. Don’t worry though, as these lichens do not hurt the tree. They simply love growing on alder bark.
Conclusion
Alnus rubra is an excellent, short-lived but extremely beneficial native tree. Plant it in an area you’d like to convert into a forest, control erosion, or simply let it grow big and enjoy its beauty. For gardeners with small yards, you can observe this tree throughout the landscape of the Pacific Northwest in all its natural glory.
Sources:
Kathleen Norris Brenzel, and Sunset Books. Western Garden Book. Oxmoor House, 1 Feb. 2007.
Kruckeberg, Arthur R, and Linda Chalker-Scott. Gardening with Native Plants of the Pacific Northwest. Seattle, University Of Washington Press, 2019.
Pojar, Jim, et al. Plants of the Pacific Northwest Coast : Washington, Oregon, British Columbia & Alaska. Vancouver, B.C., Lone Pine Pub, 1994.
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