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Pikes/Pines | The trash trees of Capitol Hill

A canopy of red alders in winter. (Image: Brendan McGarry)

A friend of mine calls alders “trash trees.” He is an arborist, and as a pragmatic person who maintenances trees to fit into the grid, alders aren’t “good” trees. They are fairly weak, short lived, are rot prone, and pop up unwanted. They are also native, and as a result host loads of other species, and possesses a subtle seasonal variability I find a beautiful part of our landscape.

These differences of opinion are well reflected in the blocked up properties of dense, urban Capitol Hill. Based on my observations, some people care dearly about managing every last inch of space, others are willing to let things go wild, and some seem entirely oblivious to the world outside their indoor spaces. (Landscaping is also a privileged act, not simply about “caring” or “not caring”). I wonder how the red alder, Alnus rubra, the common and unassuming tree, fits into our world on the Hill?

There are certainly plenty of alder trees growing around Capitol Hill. They are in the Arboretum, in St. Mark’s  Greenbelt, in Interlaken Park. However, few yards appear to purposefully invite red alders into their limited spaces. Why is this?

One of the reasons we see alders on less tended margins, is that they thrive where many trees may not. They enjoy populating disturbed areas, like an empty lot waiting for a build, with soil high in minerals but low in organic nutrients. They are nitrogen fixers, in a mutualistic relationship with bacteria of the genus Frankia living in root nodules, who pull nitrogen to the trees from the atmosphere. Alder seeds are small and flighty, dispersing from what resemble miniature pine cones by wind, readily carried long distances. These things combined with fast growth (up to six feet a year in the first five years), mean they pop up all over, wanted or not. This has given them the dubious ecological title of “pioneer species.”

Red alder wood and bark. (Image: Brendan McGarry)

Because alders make up to 60% of the hardwood cover in the Pacific Northwest and mature stands of them signal diversity and fertility, red alders are a tree to know. In winter, you’ll find finches gorging on alder seeds. In late winter, distant alders are brushed coral, their copious catkins adding a reddish wash to leafless canopies, welcome color on steely gray days. They are actually called “red” because beneath the outer layer of gray bark is a surprisingly rich red color, useful for dying.

The end grain of a cut alder log, demonstrating fast growth in its wide rings. (Image: Brendan McGarry)

This highlights the fact that alders are also valuable in the more standard ways we evaluate worth. The bark of various alder species have been valued as traditional medicine across the world. Salmon is more often than not smoked with alder. Despite being less productive than Douglas fir as a timber species (partially because it is less likely to grow in straight, single stems), alder lumber still can demand almost the same price. Woodworkers enjoy using for furniture, cabinets, bowls, and kitchen utensils (I personally enjoy carving wooden spoons from red alder).

I don’t like to boil down worth into dollars, despite the concept of ecosystem services being used to make economists care about (monetized) nature. My bottom line is that alder trees are just such good, natural habitat. Birds love them. Many songbirds nest in their branches and eat the insects which use them as host species. Short lived and are prone to rot, alders get dead tops and cavities that are vital for cavity nesting woodpeckers and owls. Looking at the bark of an alder you’ll find them teeming with lichen, a level of strata we don’t often consider, but one that is no less valuable a substrate for flora and fauna.

Alder bark with macro and micro lichens growing on it. As the tree grows, the population and diversity of things growing on it expands. (Image: Brendan McGarry)

So why don’t we have alders invite them willingly into our yards? For the literal reader, this is a philosophical question. My arborist friends would say they are hazardous, unsuitable for under power lines, and that there are more showy species. And he’s not wrong. Yet, the Hill and surrounding neighborhoods have over a 30% canopy cover and while some of that is undoubtedly red alder, in parks and greenbelts, most isn’t. I suspect the real answer is because as settlers colonized this land, it was convenient to bring reliable, known trees to this new place. I love the oaks, maples, ashes, and sycamores of our old streets and I recognize that street trees are thoughtfully chosen. However, we also unnecessarily cloister ourselves from having a better relationship with a native species.

I invite you to go out and find an alder and shake hands with its lightly leathered, toothed leaves. Investigate the details of its bark, feathered in shades of gray and green lichen. Right now, alders are showing signs of an impending fall and amid the deep green leaves are bursts of yellow; a few leaves are drifting to land as I write this. Spend some time with an alder and you’ll notice the variety of birds that mingle in their canopies. What’s not to like? Clearly I am biased, and believe in the value of red alders simply as members of the more than human community of this part of the world. What could happen if we reevaluated what species we were happy to have around us, even on the densely treed Hill? Regardless, calling red alders trash trees is unnecessarily harsh.

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6 thoughts on “Pikes/Pines | The trash trees of Capitol Hill

  1. Thanks for your piece. It’s got a good vibe. I’m embarrassed by how little I know about our neighborhood’s plants and animals.

  2. In defense of alders: they go in where other trees hesitate (clear cut land a good example) and “fix” the nitrogen due to their symbiotic relationship with certain bacteria. This readies the soil for other trees.

  3. A lot of people think of our native Red Alder as a weed tree. Thank you for letting everyone know how important this species is to our native ecosystem. This is especially true in Seattle with almost all of our natural spaces having been logged amd destroyed. I used to volunteer with the Nature Consortium and planted native evergreens and under storey in the West Duwamish Greenbelt in West Seattle. Alders fixed the soil for the next generation of conifers to survive. Unfortunately, our urban greenbelts are over run with non-native invasive species, and no seed source for the next generation of native trees and plants.

  4. “Yet, the Hill and surrounding neighborhoods have over a 30% canopy cover…”

    It’s much lower in the CH Urban Village (city-wide, multifamily residential zones were at 23% in 2016), and Downtown (10% in 2016).