Red Alder Trees

If you’ve ever cycled through Oregon, you might have passed under the canopy of a Red Alder tree. In this episode, we chat with Glenn Ahrens, an extension forester from Oregon State University, about everything related to alders and conifers. We’ll also explore various tree species native to Oregon, learn how to identify them, and discover what a forester’s favorite tree might be.


Dirty Freehub 0:06

This is the connection. A duty free hub podcast connecting gravel cyclists to where they ride through short stories about culture, history, people, places in lands.

Dirty Freehub 0:19

I’m Benjamin Pepper, and we’re here today with>Dirty Freehub. He’s an extension forester with Oregon State University. We’re talking about a species of tree called the Red Alder, which cyclists in Oregon are probably pretty familiar with. Glenn’s here to talk about alders, conifers and more species of trees you’ll find throughout Oregon. Glenn, thanks for coming on. Appreciate it.

Glenn Ahrens 0:39

Yeah, it’s my pleasure to be here. Ben.

Dirty Freehub 0:41

Tell us a little bit about yourself and your background.

Glenn Ahrens 0:43

So I am a forester and I’ve been in many types of service, but for about 40 years. Kind of surprises me. I decided I wanted to be a forester without knowing what that meant when I was 13 years old. And but there’s a lot of different ways to work in the forests. And my main background is in forest ecology and then also forest management. And I kind of had a long history starting in the late seventies when my education. So it’s been a long road for me. Currently I’m an extension forester, which really, you know, kind of the traditional extension agent your county extension office needs to be the agriculture extension agent. But in Oregon, forests are really important. So we have extension foresters and we work with private landowners and, and actually, you know, general public as well, just to help people learn about forests and learn how to manage them if that’s what they’re trying to do.

Dirty Freehub 1:35

So we’re talking mainly about read Alders here, but you have expertise and much more beyond that.

Glenn Ahrens 1:40

Yeah. So I mean, the training to be a forester, you have a real broad education and you know, all the things about trees, how they grow, how they, you know, they, they thrive, forest health, etc. and managing different forest types across the whole country. About focus in the Pacific Northwest. Then you get to know, you know, the real common dominant forest types. So the conifer forest, the great conifer forests of the Pacific coast, you know, from the redwoods up into the coastal rainforests, Douglas Fir and hemlock and Spruce are kind of the predominant species. But I got a kind of a focus on red alder and the broadleaf trees somewhat as the minority or kind of the underdogs in the in the zone are king conifers and Red Alder is actually the third most abundant tree in western Oregon for a variety of reasons, but it really thrives after disturbance. You know, wildfire, landslides, floods or logging, and it clears land and bears the soil. Alder really seeds in pretty aggressively. And it’s kind of it’s ecological role with early recovery from, you know, major disturbance. And then in the forest, it’s often seen as kind of a competitor with the conifer as if you’re trying to manage conifers.

Dirty Freehub 2:55

So can red Alders be sort of invasive into other species territory?

Glenn Ahrens 2:58

So, yeah, I mean, that it’s all in the eye of the beholder if you consider it’s not a, you know, a exotic, invasive or noxious weed in any sense. It’s just the natural colonization of a disturbed area in the forests. And that’s alders role. It’s very good at colonizing disturbed areas and bare soil, and then it fixes nitrogen and adds a lot of organic matter. And so ecologically, you often look at it as something that helps the forest recover from a disturbance and sets the stage for later stages. But from a, you know, a forester that wants to grow Douglas fir, for example, which is the number one tree that people like to plant, then the alder that comes in is seen as a weed. And so, you know, what’s the definition of a weed? It’s something that growing where you don’t want it to. So that’s more of just a human perspective on whether it’s a weed tree or a, you know, helping the ecosystem recover. But it definitely has colonized a lot of land. And the population of Alder kind of exploded after the settlement era and lots of land clearing and logging and fire and then not a lot of active management. The alder kind of came in and grew to be maybe ten times the abundance that it was, you know, a hundred years ago.

Dirty Freehub 4:14

So as not to cause any problems sort of ecologically.

Glenn Ahrens 4:17

Again, it’s somewhat of a you know, it depends on your perspective. One aspect of alder is that it because it does dominate quite well some of the areas in the old days when they harvested forests, you know, over a hill in Dale or across the creeks, some areas maybe have an excess of alder where we’d like to have more of the component of the large conifers that used to be there. So in terms of like stream and aquatic habitat, the alders are really important there, but we have nothing but alder and you don’t have any of the large conifers that’s seen as, you know, kind of something’s missing here. So that that was an issue in the past. I think that’s changing. The alders are fairly short lived and eventually they get replaced by the conifers or we are starting to actively manage more to kind of reintroduce conifers in the areas that are dominated by Alder. But it has been seen as an issue. Another little aspect of that is that Alder fixes nitrogen. It’s so it takes atmospheric nitrogen into the atmosphere and then through a symbiotic relationship with some organisms in its roots, it actually adds nitrogen. It basically fertilizes a site at a fairly high rate and sometimes there’s too much nitrate comes from having alder and becomes an issue for people managing, you know, domestic water systems in a watershed. If it’s a whole bunch of alders and the fall rains come and wash a bunch of nitrate and they have trouble with their, you know, water, water treatment and purification, you know, that’s kind of an unusual aspect of it. It’s not a real widespread problem. But, you know, those are examples of how people might view, you know, too much alder is a bad thing.

Dirty Freehub 5:52

Can you tell us what these trees look like, how you might identify one if you’re maybe writing by?

Glenn Ahrens 5:57

Well, for one thing, are Broadleaf tree, and so they lose their leaves in the winter. So actually you can if I were riding a bike through an alder stand in February on a sunny day in the coast range, which believe it or not does happen, can be quite nice actually. You get a lot of sunshine because the leaves are gone. Whereas if you’re riding underneath a Doug for Hemlock Forest, it’s very shady and you know, wet and cold. So you can actually get some sun in under the alders in the winter, but they look a lot like birch trees. So I think a lot of people have an idea of what Birch looks like with in the case of Alder, the bark can be anywhere from a white to a mottled green, gray and white color. A lot of that depends on the lichens and things that are on the tree bark that changes the appearance. But it’s so it looks kind of like a stand of birch. The leaves are, you know, kind of that oval shaped, you know, 2 to 4 inches, you know, across and and in length and little serrated edges on them. So it looks a lot like a birch. It’s in the birch family.

Dirty Freehub 6:54

So you mentioned the coast range. So these trees are mainly going to grow on the western side of the sort of Pacific Northwest, right?

Glenn Ahrens 7:01

Yeah, On the northwest, we often look at the west side of the Cascades Mountains, which start in northern California and go all the way up into northern Washington. So that’s kind of the more moist side. But there are some drier environments like in the Willamette Valley or the Puget Sound area, that things dry out a little bit. But generally, Alder is focused on the west side. There is actually some outlying kind of northwest forest types up in northwest Idaho and Montana, and you actually find some red alder up in Idaho.

Dirty Freehub 7:34

But as a forester, are there any ongoing problems with Red Alders or any other tree that you’re sort of working on or worried about?

Glenn Ahrens 7:41

Yeah, I mean, I have a lot going on as a forester and as you might imagine, you know, the Douglas fir and the conifer forests are really kind of the predominant topic that people are interested in because that’s mostly what we have. The Alder at its peak was over 10% of the forests in western Oregon, which is a pretty sizable portion for any one tree. And now it’s sort of diminished down to closer to five 6%. As forest grow older, alder ages out or foresters grow Douglas fir instead. And in perspective, you know, the Douglas fir is more like 60% of the forest. So it shows you how predominant that is. And so I have a, you know, research and demonstration and education going on. It relates a lot of aspects of forestry. But I still kind of expect to be, you know, the ALDER specialists because of my history with some of the research that we did. And we have some long term plots now of trees I planted over 30 years ago. We’re still revisiting and we’re studying how alder grows in a in more of a managed stand context or how it grows in mixtures that are intentionally kind of mixed together with Douglas Fir, for example, another, you know, kind of key topic with alder is its role in the ecosystem kind of more in the larger picture, is it? As so much of the landscape has been disturbed and now it’s recovering, it’s growing older Alder is disappearing and aging out. There might be some question about, you know, how to rejuvenate and sustain a bit of an alder component. If the forest continues to age and alder kind of phases out. There’s also questions about for all the species about climate change. So that’s on top of our minds is how do we sustain forests and keep forests healthy with the climate change causing stresses and strains and, you know, drought and heat and insects and disease are actually causing increased problems in Red alder because it’s sensitive to heat and drought particularly. But you know, in all of our forest types, we’re really looking at how much is the climate going to change, how is that affecting trees and how how do we keep forests healthy?

Dirty Freehub 9:44

So you mentioned the red alders are sort of resilient to some disturbances, but climate change is not really one of them then.

Glenn Ahrens 9:51

Yeah, I mean with alder and other species, if trees are locally adapted to the climate, you know, and in this area over the last five or 6000 years, the kind of classic conifer and alder force that we have have had a fairly stable climate. But now that there’s a shift, we may see that, you know, some trees may need to be moving up in elevation to where conditions are cooler and moister. If things get too warm and dry at lower elevations or that things are moving, you know, the environment is moving northward, you know, it’s getting warmer and drier here. And let’s say here in Portland area, the climate here may in 50 years, maybe more like it is, you know, 200 miles south, which, you know, as a warmer, drier environment. So how are the forests going to adapt to to that? Because the current forest, 200 miles south of us are very different, you know, much drier type of forest. So can we kind of keep up with that or help the species move with climate change?

Dirty Freehub 10:4

So this might be silly to ask a forester, but do you have any favorite tree species that you see around?

Glenn Ahrens 10:5

It sort of changes with my mood and also just what I’m thinking about. I have to say that coast redwoods, you know, that live thousands of years are adapted to fire. They’re just huge, amazing trees. I grew up in California and Northern California is where I studied, started studying forests. And of course, the redwoods are just something that, you know, really blows you away with how great they are and their adaptations and such. So Redwoods, one of my favorites, but I love so many different trees. It’s hard to say on a given day.

Dirty Freehub 11:2

All right. Well, we’re covered a lot. Is there anything else that you think we should know about these trees or any of your work?

Glenn Ahrens 11:3

I think just have a great appreciation for the the trees and what they do for for our environment, for the ecology and and try to keep your trees thriving and plant a tree for the future.

Dirty Freehub 11:4

All right. Thanks, Glenn. Appreciate it.

Dirty Freehub 11:4

All right. Thanks, Ben.

Dirty Freehub 11:4

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