Alnus rubra is a broad leafed, deciduous flowering tree. It is the largest of the Alder trees living in North America.
Description:
A. rubra grow quickly, potentially reaching a height of 25 m. The trunk of the tree is thin, grey-green and smooth. Mosses and lichens often grow on the bark, giving it a blotchy appearance (Pojar & MacKinnon 1994). The bright green leaves are broad, oval-shaped with edges that are jagged like a saw (MFLNRO n.d.). The veins in the leaves are parallel and easily noticeable. Flowers form in drooping clusters or catkins. The male catkins produce profuse amounts of pollen (which many people are allergic to), while the smaller female catkins are shorter and look like small brown cones (Pojar & MacKinnon 1994).
Ecology:
Red alder is found along the entire west coast of British Columbia and beyond, from Alaska to California (Harrington 1990). It grows where there are high levels of annual precipitation or in habitats where streams or ponds create humid conditions. It is tolerant of a wide range of temperatures (-30°C to 46°C ) and soil types (Harrington 1990), but is not tolerant of shade. In disturbed areas where the vegetation has been removed, dense stands of red alder can be found. In nutrient poor sites, red alder develops a symbiotic relationship with the nitrogen-fixing bacteria Frankia, which convert inorganic nitrogen in the soil into a form that is useful to red alder and other nearby species (Winship & Tjepkema 1985).
Red alders are relatively short-lived trees, living for 50–70 years before succumbing to disease and insect attacks (Harrington 1990). The standing dead alders provide habitat for many other species, such as fungi and insects (beetles and ants), feeding sites for woodpeckers, and nesting sites for small rodents and owls.
Red alders are relatively short-lived trees, living for 50–70 years before succumbing to disease and insect attacks (Harrington 1990). The standing dead alders provide habitat for many other species, such as fungi and insects (beetles and ants), feeding sites for woodpeckers, and nesting sites for small rodents and owls.
Reproduction and Dispersal:
Following pollination in the spring and the subsequent fertilization of the female reproductive structures, the catkins develop into woody cone-like fruits. A winged seed forms on each of the cone scales. Large numbers of alder seeds are widely dispersed by wind in the fall (Harrington 1990).
References cited:
Harrington CA. 1990. Alnus rubra Bong. In: Burns RM, Honkala BH, tech. coords. 1990. Silvics of North America Vol. 2, Hardwoods. Agriculture Handbook 654. US Department of Agriculture, Forest Service, Washington, DC. [accessed 2018 Jan 22]. https://www.srs.fs.usda.gov/pubs/misc/ag_654_vol2.pdf.
[MFLNRO] Ministry of Forests, Lands and Natural Resource Operations. n.d. Tree book, Learning to recognize trees of British Columbia. Douglas fir Pseudotsuga menziesii. [accessed 2017 Jan 31]. https://www.for.gov.bc.ca/hfd/library/documents/treebook/douglasfir.htm.
Pojar J, MacKinnon A. 1994. Plants of coastal British Columbia: including Washington, Oregon & Alaska. Vancouver: Lone Pine Publishing.
Winship LJ, Tjepkema JD. 1985. Nitrogen fixation and respiration by root nodules of Alnus rubra Bong.: Effects of temperature and oxygen concentration. Plant and Soil. 87: 91-107.
[MFLNRO] Ministry of Forests, Lands and Natural Resource Operations. n.d. Tree book, Learning to recognize trees of British Columbia. Douglas fir Pseudotsuga menziesii. [accessed 2017 Jan 31]. https://www.for.gov.bc.ca/hfd/library/documents/treebook/douglasfir.htm.
Pojar J, MacKinnon A. 1994. Plants of coastal British Columbia: including Washington, Oregon & Alaska. Vancouver: Lone Pine Publishing.
Winship LJ, Tjepkema JD. 1985. Nitrogen fixation and respiration by root nodules of Alnus rubra Bong.: Effects of temperature and oxygen concentration. Plant and Soil. 87: 91-107.