Red Alder -- Alnus rubra — Plant in Place

Throughout the forested land of the Pacific Northwest west of the Cascade Mountains, red alder (Alnus rubra) is one of the most important plants. Despite their importance, they are generally overlooked because there really isn’t anything particularly striking about them. In fact, most people either don’t think about them at all or consider them a weed, an unwanted and persistant presence invading a manicured garden. But it is this weed-like quality that makes them so important in the wild landscape. Red alders are workhorses, humbly fulfilling their ecological role. They are a pioneer species, growing quickly as a landscape resets after destruction. They make significant contributions, making life possible for others while taking advantage of the favorable but fleeting conditions under which they thrive. They are the driving force of renewal in the forest and without them these places would certainly be very different.

Pioneer plants are notable for role that they play in a fundamental natural process called ecological succession. Change is a part of every habitat and although natural systems are dynamic, they are a not chaotic. The steps in ecological succession are generally predictable and repetitive, though climatic, geologic, and human forces can complicate things. In a forest, ecological succession is a cycle that has two basic stages: growth and destruction. Growth is divided into several steps each characterized by different dominant plants and age distribution as an area transitions from young to old forest. It is a process that can be carried out over centuries, over a thousand years even, until a forest eventually achieves its climax vegetation community and becomes a mixed-age old-growth habitat. It is also a process that can come to an abrupt end at any moment, either after old-growth habitat has become established or as the forest is still young. A strong wind storm, earthquake, wildfire, avalanche, pathogen, or any other number of natural or man-made disturbances can occur in an instant. This is the destruction, and whether widespread or localized, landscape is altered. If life followed a straight line, this would be the end. Thankfully it is simply a reset. It is the beginning of renewal, the first step in growth and the time for pioneer species.

In the forest, pioneer species like red alders are generally transitory. They are capable of growing quickly, feet per year in ideal conditions, and reproduce rapidly in the sun-filled openings left by destruction. They have a small window, both in time and space, in which to exist. The story of early forest succession is really a story of wave after wave of different plants shading each other out of existence. Red alders themselves are not the very first plants on the scene after destruction. Much faster growing herbaceous plants like fireweed (Chamerion angustifolium) establish almost immediately. After a few years they are shaded out by taller yet slightly slower growing plants like red alders. Likewise, as red alders are getting established, later-succession plants, the evergreen trees like western hemlock (Tsuga heterophylla), are already saplings below them. Growing slowly, inching up year by year, intractable and capable of reach greater heights, these evergreens will eventually overcome the red alders and establish an even-aged evergreen canopy overhead. The deep shadows cast by a dense even-aged evergreen canopy makes life below impossible for sun-loving plants like red alders. So like many other pioneer species, red alders are short-lived. Typically reaching 70 years with some pushing on toward 100, red alder closely mirrors the lifespan of a typical 21st century human.

Red alders between a river and evergreens.

Over the course of their relatively short lives, red alders make great contributions to the landscape. The most basic but perhaps more important of these contributions is to act as a literal place holder. In mature forests, the enormous trees form great mats of interconnected fibrous roots just below ground. This tangled root mass grows in search of water and nutrients but also secures soil, holding it in place. In the wake of a destructive event, fibrous surface roots quickly shrivel and die, leaving the land susceptible to soil erosion. Heavy rain washes soil downhill, drying sunlight and unimpeded wind blows it away. It is important that a mass of roots reestablishes quickly as the habitat resets in order to secure the soil and provide a stable home for later generations of plants. Red alders happily play that role. Meanwhile, they also carry out an important chemical process that benefits the soil. Like humans, plants require a mix of nutrients in order to function and of these, nitrogen is the single most important for growth and basic functioning. Though overwhelmingly abundant in the atmosphere, plants cannot make use of atmospheric nitrogen. In the soil, in the form that plants can use, nitrogen is much less abundant. Certain plants, famously legumes, are able to fix atmospheric nitrogen into the soil where it can be used by plants. Red alders also fix nitrogen into the soil through a complex root association they form with bacteria called Frankia. Of course, the fixed nitrogen that red alders provide is first and foremost for their own benefit. But for whatever reason, their nitrogen fixing capability far out matches their needs and the vast surplus is left to the benefit of other plants. Like a bag of manure added to a vegetable garden in the spring, this fixed nitrogen gift is a boon to plant life in a regenerating forest. Red alders also contribute nutrients and organic matter to the forest floor every autumn as they drop their serrated brown-yellow leaves, which build up year after year and add to the health of the land and provide the organic-rich topsoil that many climax evergreen species require for germination.

The importance of red alder to animals should not be overlooked. Thickets of young alder shoots provide abundant and accessible forage for deer and other woodland herbivores. These same thickets provide great cover for birds and small animals from predators and are home to the many insects that they eat. Red alders even have an impact on aquatic life. Excessive soil erosion can impact mountain streams by overloading them with particulates, increasing turbidity in water that is normally very clear. Increased turbidity lowers sunlight infiltration and reduces visibility for aquatic animals, including the salmon which return every year to spawn in the streams and rivers of the Pacific Northwest. Fry, the baby salmon born in these streams, need to eat a lot before heading out to sea. The more difficult it is to see, the more difficult it is for them to catch their prey. Eating less, fewer survive and the population is impacted. By holding and improving soil, providing food and shelter, red alders lead influential lives.

Male flowers below the smaller female flowers and emerging leaves on an alder.

Stands of red alders can take root across Pacific Northwest forests in sun-filled openings left in the wake of large disturbance, but in natural areas they are most frequently found along the banks of large rivers that drain the high peaks and valleys of the Pacific Coast Ranges. The area immediately surrounding a river, the riparian zone, is ideal red alder habitat for a number of reasons, and first among those is that riparian zones are tumultuous places. Every spring, these rivers swell with water as an almost unfathomable amount of mountain snow begins to melt. Frozen in place throughout the winter, sunshine and warmth combine with gravity to unlock the potential energy of half a year’s worth of precipitation. As the spring torrent flows down to the ocean, water works away at the banks causing some erosion. Flooding is also common as spring melt overflows the river banks. These short periods of standing water makes life difficult for young saplings of the various slow growing evergreen trees that inhabit the forests. Red alders and other pioneer species are able to withstand some flooding and relatively poor soil so that ironically, they find stability in disturbance. For that reason, river banks are generally where you find the largest and oldest red alders.

Although they may not be remarkably beautiful plants, red alders do possess some notable visual qualities and are in their prime from midwinter through early spring. During the winter their bare canopy is filled with subtle red vegetative buds which will become leaves, stems, and flowers over the course of the year. Taken individually, these buds don’t make much impact but in their thousands, filling the canopy, they do. Because the winter landscape of the Pacific Northwest is mostly green and grey, it doesn’t take much red to stand out. Mostly lost in the harsh light of midday, red alder canopies are more likely to catch your eye as the setting sun casts beams of light horizontally across the land, causing the canopy to glow red. Emerging in spring, the male flowers are graceful pendulant catkins of yellow-green marked with red. The female flowers are much smaller and held erect just above the male flowers. As the leaves emerge, the canopy transitions from subtle red to light green, a good spring color.

A red alder trunk is a masterpiece and like the canopy, it stands out best in winter and spring. The actual bark of the tree is a relatively smooth dull-grey nothing, but like a canvas covered with paint, red alder bark is simply the base, obscured by layers of other life. Looking at a trunk of a mature red alder, you are looking at much more than a tree. Here are lichens and mosses. These organisms make a little world onto themselves and close inspection of a red alder reveals that they are diverse and intricate assemblages. Big splotches of white rim lichens (Lecanora spp.) can cover the trunks and give them a mottled appearance, white and grey. The circular fruiting bodies of rim lichens give the trees texture. Bark barnacle (Thelotrema lepadinum), a lichen that genuinely looks like barnacles, can also make a home on red alder. Small scribbled black lines, like text of an unknown lichenous language, script lichen (Graphis scripta) is found scribed over the white rim lichens. Atop the bark and lichen, a layer of moss generally thicker toward the base of the tree, ranges up and down its length with tufts of soft green. Of the various mosses found on any given red alder, the little fern-like leaves of Oregon beaked moss (Eurhynchium oreganum) appeals to me the most. A real fern, licorice fern (Polypodium glycyrrhiza) also find a home on red alder, clinging to the trunk where it can find adequate anchorage for its wandering rhizome.

Seeing these life-covered trunks in tight stands, stalks of stark white surrounded by dark and moody evergreen forest, is magical. Wading in and not being able to see through to the other side, there is mystery and a little bit of something else, like unease. They play a trick on your eyes, have a slightly dizzying effect. It is hard to gauge the depth of them and though I’ve never walked through an alder stand large enough to get lost in, I have felt that eerie sense of disorientation. In lining the banks of the rivers that link deep forests and the ocean, stands of red alders act as an entryway and a sort of time portal. Forest edges are interesting places because walking through them is like time traveling through the stages of ecological succession. From the chaotic disturbance of the rock-strewn mountain stream, stepping up onto the bank you are immediately confronted by young and dense red alders stands along with other early pioneer species. Contorting through these tightly packed stands with their low branches, arms raised to shield your face from their scratching arms, you finally break into older and larger red alders which are spaced farther apart and have few low branches. Continuing onward, you come to an even more open landscape of big red alders mixed together with towering bigleaf maples (Acer macrophyllum). Some of these red alders are dead, either standing as snags or lying on the forest floor. Also growing here are some younger evergreen trees. Going just farther, you are greeted by the darkness of the established mixed evergreen forest, where no red alders are found.

The ecological importance of red alder is nearly matched by its value to humans. Native Americans have long put these trees to use in food preparation and medicine. The wood can be worked into any number of small but useful things like plates, bowls, utensils, furniture, and many tools that makes life easier. Canoes and paddles are also made from red alder. The inner bark, below the layers of lichen and moss, below the grey outer bark, is a deep red that is perfect for creating various shades of red, orange, and yellow dye. These dyes have both decorative and practical applications. Red alder boards and chips are commonly used when smoking or grilling salmon, imparting their unique flavor into the fish. Since European settlement in this area, red alders have become important in the timber trade. Although they don’t make great lumber, the wood being too soft, they are great for many lightweight applications like cabinetry, flooring, and paper production. And with their rapid growth rate, they need much less time from sapling to harvest than slow growing evergreens, offering a shorter wait between valuable harvests.

Red alders are one of so many overlooked plants. We don’t notice them because we are looking for something more exciting. They are the green filler, background noise, normal somewhat boring trees. But very often these boring plants are vital in sustaining habitat, providing home for the prettier plants and interesting animals. That forests naturally exist is something that we take for granted, but they do not just happen. Remarkable and obscure processes create and sustain them, things that we don’t generally think about but really should. Everything is interconnected and everything plays some role in sustaining the systems which make up the natural world, so it is not really correct to say that anything is more or less vital than anything else. But it is true that some species carry more weight and have larger impacts than others. Red alders are not particularly flashy, they are not awesome to behold, they are considered weeds by gardeners, a simple commodity by foresters, and completely ignored by most. But they do lay the groundwork, making majestic old-growth forests possible. They do add something to the landscape with their intricate trunks and subtle canopy. Ultimately though, their truly awe-inspiring beauty is seen not directly but indirectly in all of the wonders found in the Pacific Northwest forest.