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I had just moved back to British Columbia from Ontario and was looking for a forest to explore. There are many lush rainforests along the BC coast and I will be exploring all of them over time. This day, I chose to drive inland from Ladner to Campbell Valley Regional Park, where I’d been horseback riding years ago.

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This time, I took the north entrance and dispensed with the horse to take the slow way—walking—to explore the fractal forest, both large and small. I started with the Little River Loop Trail, which took me through a lush forest (large Douglas firs, cedars, Bigleaf maples and vine maples with huckleberry and Oregon grape undergrowth) and twice crossed the winding Little Campbell River marshland along boardwalks.

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I hadn’t gotten very far, just to the forest verge on the edge of the marsh, when I noticed six large deciduous trees with fairly smooth, shallowly furrowed, bark. The largest and oldest tree showed some bark separation into irregular flat plates. The trunks were covered in moss and a plethora of mostly crustose lichen. I immediately thought of the two old beech trees covered in crustose lichen in the Mark S. Burnham Forest, Ontario, that I’d documented a while ago when I lived there. According to lichenologist Joe Walewski, an abundance of crustose lichen on a tree signifies maturity. While crustose lichen tend to be the first colonizers of rock, they are later colonizers of trees. So, these trees were quite mature.

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But these couldn’t be beeches, I thought, despite the smooth bark and similar looking leaves—the beech tree isn’t normally found here. I thought briefly of a yellow or paper birch but the bark and the leaves also didn’t match. It took me a while to realize that these were my old friends from BC, the red alder (Alnus rubra). The deep veined leaves with scalloped edges matched; but it was the distinctive female catkins that I found on the ground that provided incontrovertible proof. Of course, it made sense that these trees flourished by the marsh—alders love water. And what better tree to feature on my return to British Columbia than this colourful and highly successful representative of my new home.

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This scrappy, short-lived tree (grows to a maximum age of 75 years achieving a dbh of 60 cm and a height from 15-30 m) springs up quickly in disturbed places, growing rapidly and forming dense thickets of saplings in varied habitats—giving it the reputation of being a ‘weed tree.’ But the red alder is so much more…

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Early Succession Pioneer Trees

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In truth, the red alder serves an important role in succession as a pioneer (early sere) species, often the first colonizer of a disturbed area—from fire, logging, flooding or avalanches. Plant in Place calls them “the driving force of renewal in the forest,” and goes on to describe the alder’s place in both growth and destruction cycles inherent in all ecological succession.

Like moss, lichen and some fungi, alder trees thrive in places that have been burned or swept away, areas of disturbed mineral soils and often copious sunlight. Pioneer species play a key role in creating habitat for later sere species by building soil and providing shade for other plants to establish, ultimately increasing biodiversity in ecosystems. The red alder also forms a partnership with bacteria that fix nitrogen from the air through nodules that form on its shallow wide-spreading root system; these make nitrogen available for plant growth and allows the red alder to grow in poor soils that lack nitrogen. providing the ecological service of adding nitrogen to the soil. As the forest matures, the short-lived alder gives way to the shade of the slower growing tall conifers such as Douglas fir and cedar. Dead alders continue to provide habitat for wildlife and the nutrients released from the rotting wood become available to other fungi, animals and other plants.

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Red Alder Habitat & Distribution

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The red alder It is a costal tree and only appears within a narrow band within 150 km of the Pacific coast in Canada. Its preferred habitat is a floodplain and along streams. The red alder is naturally found in moist forests, around marshes and swamps, or along stream shorelines and ranges from southeast Alaska to southern California, from sea level up to about 2,500 feet elevation. It generally occurs within a hundred miles of the coast. It often forms pure stands, but also commonly mixes with black cottonwood, grand fir, Douglas-fir, western redcedar, western hemlock, western yew, bigleaf maple, and vine maple—all of which occur in Campbell Valley Park.

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Red alders prefer sunny areas that aren’t too dry and where the seeds can germinate and grow fast. It does not tolerate very dry sites but can live in wet and soggy soil. According to The Natural Edge, Red Alder grows best in moist to wet conditions with full or partial sun exposure with pure alder stands often occurring along streambanks. It prefers sand or loam soils but can grow in a variety of soil types. It can tolerate poor soil, steep slopes, drought, and periodically flooded areas. Because of this, river banks are generally where the largest and oldest red alders occur. My alders were very well placed, on the forest verge with the marshland. Fairly sunny and wet.

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The trunk diameters of the six red alders I looked at measured with smaller ones from 18 to 20 cm dbh and two larger trees from 35 to 51 cm dbh. Based on the literature, I estimated that these trees ranged with smaller ones from 19 to 26 years old and two larger ones from 36 to 55 years old. A good stand of mature alders.

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Red Alder Life Cycle

The red alder is monoecious, bearing both female flowers and tassel-like male catkins. The male and female catkins emerge before the first leaves in spring (February), creating an orange-red haze around the bare branches of an alder stand. Yellowish male catkins dangle with tiny red flowers. Their pollen blows in the wind onto the less conspicuous green female catkins. As the female catkins mature and develop seeds in summer, they turn brown and resemble small pinecones. The tiny, winged seeds disperse in the wind and are spread by birds and other animals. Many are eaten by birds or mice, killed by drought, consumed by fungus, or just land in a bad spot.

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Red Alder Human Uses & Mythology

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The red alder is often used in restoration projects for its fast growth, soil stabilization and nitrogen fixing abilities. According to the USDA, Red alder is an excellent species for re-establishing woodlands.  The trees are used in forested riparian buffers to help reduce stream bank erosion, protect water quality, and enhance aquatic environments.  Plantings of red alder are effective in controlling erosion on steep slopes in disturbed areas (Uchytil 1989).  These fastgrowing trees help to prevent soil erosion because of their dense canopy cover and thick litter layer that forms within the first 3 to 5 years.  The leaf litter is high in nitrogen content (Labadie 1978).

Indigenous people use the wood of red alder to make canoes, tools, and cooking utensils. They use red alder bark to make dyes and medicines and weave its fibrous roots into baskets. Plant in Place provides more details on this tree’s many uses.

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Alder Bark Ecosystem

The bark of red alder is relatively smooth and whitish-grey. But the bark is often obscured with a rich variegated carpet of moss and lichen—forming a diverse ecosystem worth investigating.

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Mosses

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I identified several mosses that colonized the red alder’s trunk. As with many other trees, mosses were most abundant at the base of my alder trees. Mosses I identified included Feather Moss (Brachythecium spp.) and Oregon Beaked Moss (Eurhynchium oreganum) with its small fern-like leaves, known to commonly occur on red alder trees. 

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The most dominant moss, from the tree base up the tree was Cat-tail Moss (Isothecium myosuroides) with their ‘tails’ swinging down in waves. I also noticed Tree Ruffle Liverwort, Porella navicularis (an old friend I’d seen growing at the base of several old sugar maple trees in Ontario), growing among the Cat-tail moss.

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Farther up the tree, I found patches of Dusty Fork Moss (Dicranum fuscescens) and Pincushion Moss (Ulota crispa).

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I’m also told that the licorice fern (Polypodium glycyrrhiza) tends to colonize red alders, though I did not find any on the alders I investigated.

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Lichens

These large old red alders were literally covered in corticolous lichen. Most lichen were crustose—suggesting mature trees—but I also found several fruticose and foliose lichen.

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Tree Flute Lichen (Menegazzia subsimilis)* is a common foliose macrolichen in the Parmeliaceae and fairly common throughout the world, often found on rocks and trees, and frequently on red alders in British Columbia. It is also called honeycombed lichen (due to its distinguishing feature of having holes. I originally identified it as Monk’s Hood Lichen (Hypogymnia physodes) a common lichen in boreal and temperate forests of the northern hemisphere, which also inhabits red alders. Both resemble one another greatly, sharing commonalities in a thallus that when dry is grey to yellowish-green and loosely attached to its substrate; and when wet the thallus turns deep sea-green as the algal partner actively photosynthesizes. Both have hollow lobes, often brownish toward their margins that are often turned up and covered in white powdery soredia. The lower part of the thallus is black and the lichen has abundant tiny black pycnidia that resemble pepper granules on the upper thallus towards the tips. What differentiates these two is the presence of holes on the upper surface of the thallus of Menegazzia subsimilis, a diagnostic feature easily recognized once identified.

*This identification was made thanks to a suggestion made by “MagnificentSweetly” (see comments section below), which I confirmed through the literature.

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Bark Barnacle Lichen (Thelotrema lepadinum) is a crustose corticolous lichen often reported on red alder bark, that forms creamy grey-white crusts on the surface of tree bark. The apothecia of this crater lichen genuinely resembles barnacles, with a thick outer rim and thin papery inner rim. Italic 8.0 describes the apothecia as “conical thaline warts” with a “crater-like summit, the rim usually incurved, with a whitish membrane at the bottom which disrupts at maturity, leaving small, white fragments in the centre of the blackish apothecial disk.” Its genus name—Thelotrema—is from the Greek words meaning “perforated nipple.”

Barnacle Lichen is frequently found on bark of red alder and both thrive in humid, oceanic environments of the Pacific Northwest. Cumbria Woodlands indicates that Barnacle Lichen’s preference for red alder is partly because it prefers smooth bark. Italic 8.0 notes that, in Europe, Barnacle Lichen is often found on the smooth bark of beech and acidic bark of fir. Red alder bark is both: smooth and mildly acidic.  Woodland Trust writes that this lichen is “found mainly on the bark of living trees in ancient woods, and it is indicative of longstanding woodland conditions.” Atlas of Czech Lichens notes that this lichen usually grows on smooth acidic bark of older deciduous trees and is a bio-indicator of old-growth forests.

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Smooth Saucer Lichen (Ochrolechia laevigata), also called Crabseye Lichen, is a crustose lichen often found on red alder bark in the Pacific Northwest. The lichen typically has a smooth, white to greyish thallus with distinctive pimples’ of the spore-producing apothecia scattered throughout its surface. The apothecia are saucer-shaped disks of yellow-brown to orange rimmed by lighter margins. This lichen seems to prefer alder, but can also be found on vine maple and some other deciduous trees.

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Common Script Lichens (Graphis scripta) are a crustose lichen with grey-green powdery thallus and found abundant on the large old alders I investigated. The script lichen is characterized by and gets its name from the darkish strange raised squiggles that resemble short scribbles that look like a secret alphabet on the thallus. the dark squiggles are actually elongated and narrow spore-producing apothecia. The lichens start rather inconspicuously as grey smears on a tree; eventually the grey thallus develops visible squiggles of apothecia that look like a pair of lips, called lirellae. The script lichen prefers the smooth bark of the alder tree or young maple or poplar on which to ‘write’ its story.

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Orange Rock Hair (Trentepohlia sp.) is a green alga often serving as the photobiont of lichens, but also often occurring as an independent subaerial alga that obtains its nutrients form humidity, rain and sunlight. This green alga commonly grows on alder trees, forming felt-like orange patches on the smooth alder bark. The orange colour comes from carotenoid pigments that mask its green chlorophyll. I previously documented the Red Bark Phenomenon caused by this dynamic green alga when I discovered it on several poplar and hemlock trees in some Ontario forests with the article, “When Green Algae Turn Red: The Red Bark Phenomenon.”

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References

Cheah C. and Li D.W. (n.d.). “The Red Bark Phenomenon.” CAES. The Red Bark Phenomenon (ct.gov)

Cheah, Carole. 2016. “The Red Bark Phenomenon.” (PDF) The Red Bark Phenomenon (researchgate.net)

Government of Canada. “Red Alder”. Website, last modified 2024-11-12.

Jenkins, Jerry. 2020. “Mosses of the Northern Forest: A Photographic Guide.” Comstock Publishing Associates, Cornell University Press, Ithaca. 169pp.

McCume, Bruce and Linda Geiser. 2023. “Macrolichens of the Pacific Northwest” 3rd edition. Oregon State University Press, Corvallis. 549pp.

Sanders W.B. & Masumoto H. 2021. “Lichen algae: the photosynthetic partners in lichen symbioses.” The Lichenologist 53: 347–393.

Uchytil, R.J. 1989.  “Alnus rubra”. In: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory 2001, May.  Fire Effects Information System, [Online]. Available: http://www.fs.fed.us/database/feis/ . 2002].

USDA. “Silvics of North America: Red Alder” USDA Forest Service. Website

Walewski, Joe. 2007. “Lichens of the North Woods.” Kollath & Stensaas Publishing, Duluth, MN.

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