RED ALDER

by Thomas & Sara Noland
Summer 2020
Photos by Thomas Noland except as noted
Spring sunlight illuminates the new leaves of a red alder. The leaves have deep veins and scalloped edges.
Spring sunlight illuminates the new leaves of a red alder. The leaves have deep veins and scalloped edges.

RED ALDER

by Thomas & Sara Noland, Summer 2020

Photos by Thomas Noland except as noted

Call it a weed tree if you want, but red alder is essential to the ecology of Puget Sound forests. Its roots build nutrients in the soil, its bark and twigs provide food for wildlife, its fallen leaves and branches create a blanket of rich mulch on the forest floor. The trunks provide habitat for many lichens and mosses which in turn provide homes for insects.

The red alder tree, Alnus rubra, grows in Pacific Northwest forests. If not logged or killed by a wildfire or other catastrophe, it might live about as long as a very lucky human being, up to about a century. Most don’t live that long. Unlike ancient conifers that tower in the old-growth forests of the Olympic Peninsula, whose massive trunks and branches reach into the clouds over the span of centuries, red alders are fast-growing, scrappy, and short-lived. It’s not surprising that the red alder, which can seemingly grow anywhere, forming dense thickets of saplings whose trunks and branches seem to sprout overnight and then break off during the next windstorm, has a reputation as a weed.

Red alder ranges from southeast Alaska to southern California, from sea level up to about 2,500 feet elevation and generally within a hundred miles of the coast. It can’t survive on very dry sites but can tolerate wet soil. It’s most commonly found mixed with other trees such as Douglas fir and western hemlock. Pure alder stands can also be found, usually in moist places such as gravelly streambanks.

Red alder favors moist soil and can colonize gravelly stream banks.

Of the ten species of alder in the United States, only our red alder grows abundantly or large enough for commercial use and is considered one of our most important hardwoods, used for furniture and cabinets and other products. Long before the lumber industry arrived here, Northwest tribes made extensive use of red alder, making canoes, tools, and cooking utensils from its wood; using its bark to make dyes and medicines; and weaving its fibrous roots into baskets.

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Male red alder catkin in the rain

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Ripe female catkins from last year between male red alder catkins.

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Female and male catkins still on the tree.

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Ripe female catkins with their seeds.

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Closeup of seeds compared with the head of a pin.

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Closeup of male catkin.

an early spring start on life

Red alder trees get an early start on reproduction each year. Male and female catkins (reproductive parts) emerge before the first leaves in spring, creating a reddish haze around the bare branches of an alder stand. Up close, male catkins are yellowish, long and dangling, full of tiny red flowers. Pollen from the male catkins is wind-blown onto the less conspicuous female catkins, after which the male catkins disintegrate. As the female catkins mature and develop seeds throughout the summer, they turn from green to brown and look like clusters of small pinecones. The tiny, winged seeds (over 600,000 seeds per pound) are dispersed by the wind as well as by birds and other animals. This tremendous productivity is a hedge against the fact that many seeds will be lost, whether eaten by birds or mice, killed by drought, consumed by fungus, or just landing in a bad spot.

a pioneer species

Red alder is a pioneer plant species, taking advantage of drastic changes in the landscape, such as fire, logging, flooding, and avalanches. It can thrive in areas where the vegetation was burned or swept away, leaving behind disturbed mineral soils and lots of sunlight. Red alder’s ability to colonize inhospitable places makes it a pioneer in building soil and providing shade until other species can become established. How do they manage to thrive and set the stage for the development of a new forest?

Red alders do well in cleared, sunny areas that aren’t too dry, where the seeds can germinate and start growing fast. By springing up quickly alders can outcompete slower growing species. A seedling alder can, under good conditions, grow three feet in its first year. Sapling trees, two to five years old, can grow more than ten feet per year. A 20-year-old tree may be more than 70 feet tall. The growth rate slows as the forest becomes shadier and the alder trees mature, with a maximum height around 120 feet (although many alders break off in windstorms or under snow long before then). Red alders rarely live past 100 years. While a red alder is springing up fast and tall in a matter of decades, the conifers around it grow slowly and steadily. As the pioneering alders age and die, the conifers can keep growing for centuries. Foresters speak of this as forest succession, the shift over many years from a young forest of pioneer species like alder, to a mature forest of evergreen giants.

Lichens and moss made a home on this red alder’s trunk before it fell. As a fallen log, the tree will continue to provide nutrients to the forest.
See more about lichen and alders in the article In the Company of Alders
You can also learn more about lichen in general in the article with the surprising title of Lichens.
Nodules (orange bumps) on a red alder root, where nitrogen-fixing bacteria live.

Red alder also has a special partnership with bacteria that obtain nitrogen from the atmosphere and make it available for plant growth (called nitrogen fixing). Inadequate nitrogen levels in the soil are a common limit on the growth of forests worldwide, so the ability to fix nitrogen gives red alder an advantage in poor soils. The bacteria live in small bumps or nodes on the alder’s roots and obtain nitrogen from air spaces in the soil.

See more about how Nitrogen fits into all of this in Factories Underfoot
A red alder snag with many holes excavated by pileated woodpeckers.

 

 

 

 

 

life out of death

A red alder’s importance to the forest doesn’t stop when the tree dies. Upright dead trees, called snags, provide a home for woodpeckers, chickadees, and other creatures that live or nest in tree cavities. Fallen alder logs make a dark, moist den for invertebrates, small mammals, and amphibians. A red alder tree falling over into a stream creates hiding places for young salmon. The nutrients released from the rotting wood are taken up by plants, fungi, and animals, recycling the body of the alder tree back into the life of the forest.

Sara and Thomas Noland are naturalists who live in Everett, Washington. They live in a tiny house with many cats but are fortunate to have a big yard with lots of trees, birds, and lichens. They frequently take field trips to enjoy and photograph mountains, beaches, and deserts, as well as enjoying the creatures in their own neighborhood.

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