S.7 Ep.3: The Old-Growth Project

 Many of us in forestry remember the spotted owl controversy of the 1980s — a pivotal moment that put old-growth forests of the Pacific Northwest in the national spotlight. But what’s less often told is how that same moment sparked a wave of old-growth research here in the Lake States, launching more than three decades of work to better understand how old-growth northern hardwood forests differ from those we actively manage. In this episode of SilviCast, we sit down with Julia Burton, Associate Professor of Silviculture at Michigan Technological University, to explore what we’ve learned from that research — and how those insights are shaping the future of northern hardwood forest management. 

Transcript

S7 E3 - Old Growth

[Greg Edge]

Welcome to Silvicast, the podcast about all things silviculture. I'm Greg Edge, retired silviculturist with Wisconsin DNR Division of Forestry.

[Brad Hutnik]

And I'm Brad Hutnik, Wisconsin DNR silviculturist, still working until the shoe glue no longer holds my boots together. And we're your hosts for today's show. 

[Greg Edge]

Hey, Brad, you're in for a treat today. 

[Brad Hutnik]

Oh, oh, are we going to do some more Silvicast prank calls? I've got some ideas, Greg. I've got some people we should call too. I've got a short list, but they're going to appreciate it. 

[Greg Edge]

That would be fun. But no, we're not going to do that.

[Brad Hutnik]

No. Okay. Well, could we do some fake commercials? Um, you remember like reverse Jay? Remember the early days we did like, yeah, those were popular. Those were creative too. I like that.

What was a beeline industries? You don't want to go any lower than us. That was yours.

That was good stuff. Yeah. 

[Greg Edge]

Yeah. I don't know.

My pun writing ideas seem to dry up. So no, I think what we're going to do today is we're going to try to go in the opposite direction, you know, instead of being funny, okay. Silvicast needs to be more sophisticated, more professional.

Just listen, hear me out here.

[Brad Hutnik]

 I'm sorry, Greg. I coughed on something. I heard you say professional. 

[Greg Edge]

Hear me out, hear me out. All right.

Cause I was listening to an episode of Fresh Air with Terry Gross in it. You know, the one.

Well, and she's really smooth. Like there isn't dad jokes in there and there's no stories of like dumb stuff that she does while she's out pheasant hunting.

I don't even know if she Terry gross pheasant hunts, but she did win a Peabody award for crying out loud. 

[Brad Hutnik]

What? Back up, back it, back it up here a little bit. You want us to sound like an NPR story? I'm not even sure where to begin with that one, Greg, because there's like a whole host of reasons why we shouldn't do that and let me point out, first of all, those people are professionals, right?

Like you and I, what do we do? We don't do this professionally. This is like a labor of love.

It's not a, not a professional thing that we're doing. 

[Greg Edge]

We're professionals in a way.

[Brad Hutnik]

I, I don't know, Greg, it feels to me like…

[Greg Edge]

They don't pay us for our recording voice, but they should.

[Brad Hutnik]

I don't know about that, but I don't know. NPR story. You're going to have to convince me on this one.

[Greg Edge]

Okay. Well, I think we can do this. All right. Let me hear your best NPR smooth recording voice, Brad.

[Brad Hutnik]

All right. Let me pick up a book here. I'll read something.

Higher temperatures have resulted in growing conditions. I can't even do it, Greg. I can't even, I can't even read and do something like that.

[Greg Edge]

Not exactly. Not exactly. 

[Brad Hutnik]

As discussed in our forest ecology section, disturbances are one of the main drivers of forest succession and structural change.

[Greg Edge]

That was, that was nice. That was a nice attempt.

[Brad Hutnik]

 Yeah, I can't do it.

[Greg Edge]

So anyway, we're going to introduce our guest here today. I'm going to do it in my best NPR voice.

So get set. Here we go. 

[Brad Hutnik]

I'm going to need a big coffee for this one, Greg.

[Greg Edge]

This is a new era of professional silvicast. 

[Brad Hutnik]

Oh, I'm sorry. That shiver just kind of hit me.

[Greg Edge]

Many of us remember the spotted owl controversy of the 1980s, which sparked intense interest and research into old growth forests in the Pacific Northwest. What's less well known is that those events also lit a spark here in the Lake States. At the University of Wisconsin-Madison, forest researchers, Dr. Craig Lorimer and Dr. David Mladenoff, working with colleagues from our own Wisconsin Department of Natural Resources, launched what became simply known as the Old Growth Project. In its first phase, the project set out to document the composition, structure, and function of remnant northern hardwood and hemlock hardwood old growth forests across the region. Places like Sylvania Wilderness in Michigan's Upper Peninsula, and to compare them with actively banished forests. And what they found were clear and meaningful differences in coarse woody debris and snags, vertical and horizontal forest structures, tree species diversity, fungal communities, and nutrient dynamics.

With this clear picture of what old growth looks like in the Lake States, the researchers then moved to phase two, exploring whether silvicultural techniques could be used to accelerate the development of old growth characteristics in managed forests. This foundational work is shaping how we think about forests in the region and has inspired a new generation of researchers, including our guest today, Dr. Julia Burton, Associate Professor of Silviculture at Michigan's Technological University.

[Brad Hutnik]

Thank you to our season sponsors, the Family Forest Carbon Program, and the Nelson Paint Company. You make the silvicast world go round.

[Greg Edge]

Hey, Julia, welcome to Silvicast. That was my best NPR voice, but I, I just don't know if I'm going to get a job there. What do you think?

[Julia Burton]

That was amazing.

[Greg Edge]

Yeah, thanks.

[Brad Hutnik]

We'll give you the real feedback later. Greg, that was really good.

[Greg Edge]

Uh, yeah, yeah.

[Brad Hutnik]

it was really good. You're a real trooper. 

[Greg Edge]

Okay. Well, well, hey, Julia, how are you doing today?

[Julia Burton]

Great. It's great to be here.

[Greg Edge]

For our listeners, because we know you pretty well, can you tell us a little about where you work and what you do?

[Julia Burton]

I work at Michigan Tech, Michigan Technological University. I teach silviculture courses that are required as part of our undergraduate programs in forestry, as well as applied ecology and wildlife ecology and conservation. I also have a research appointment.

So my research program now is looking at picking up on some of the long-term studies of forest dynamics and old growth, northern hardwood forests that we have here in upper Michigan. I'm also working on silvicultural experiments, looking at climate adaptation in northern hardwoods and restoration and ecological silviculture in mixed pine forests and functional traits of individual trees, species, and how that is linked to ecosystem structure and function.

[Greg Edge]

I know you got a lot on your plate.

[Julia Burton]

Yeah. I like to think of it as like three interconnected research triangle.

[Brad Hutnik]

Greg knows I'm a, I'm a big Michigan Tech fan boy. I mean, I'm, I'm a pointer, you know, in my heart, but every time I go to Michigan Tech or I see anything coming out of there, I think you guys do such a good job of, of combining like really sound undergraduate training with research, which I think that's hard to do.

[Julia Burton]

Right. Yep. They're both very important and yeah, we emphasize both here.

[Greg Edge]

I thought you were just a pointer through and through, Brad.

[Brad Hutnik]

No, no. I'm I, every time I go to, every time I'm in Houghton and I just see what you guys are doing up there, I'm like, man, this is the way everybody should do it.

[Julia Burton]

Great. Well, we'll have to get you up here again soon.

[Brad Hutnik]

Yeah, that's right. 

[Greg Edge]

So Julia, today we're going to talk with you about some of this work in old growth in the Lake States and something you've been involved in for quite some time. And so I was just wondering, how did you get started looking at old growth issues in the Lake States?

[Julia Burton]

Mm-hmm. I worked on that phase two of the old growth project in Wisconsin for my PhD, looking at ground layer plant community responses to gap size and deer on the Flambeau experiment, but I actually started learning about old growth and doing research on it when I was a master's student at the University of Minnesota, where I was doing some comparative studies, comparing old growth forests on the North shore, these are Northern hardwoods, to younger second growth stands in order to develop silvicultural practices to help restore those characteristics.

So it was a pretty natural fit for me to move from that to phase two in Wisconsin.

[Brad Hutnik]

What was the overall purpose of that phase two with the Flambeau experiment?

[Julia Burton]

The overall purpose was to look at the differences that we saw in composition and structure and function between old growth and younger second growth and managed forests and those comparative studies and kind of move to an experiment where we looked at methods of restoring those structures in second growth stands.

[Greg Edge]

So I always kind of get this confused too. So the Flambeau experiment was simulating maybe some of those disturbances to try to emulate some of those characteristics that they found when they looked at the original old growth stands.

[Julia Burton]

Right. So the old growth stands had in particular, what stood out was that there was a larger range of canopy gap sizes and bigger canopy gaps than younger second growth and managed forests, as well as a lot more coarse woody debris and snags. And so it looked at what if we manipulate those two factors and really zoom in and look at the ecological processes and what are the mechanisms by which those affect the forest.

And then the companion study, the moss experiment, the managed old growth silvicultural experiment kind of scaled it up on more of an operational scale, developing different silvicultural prescriptions that would actually be applied. Whereas the Flambeau really kind of zoomed in on the ecology and the mechanisms is kind of how I look at it. I don't know if you have a different.

[Greg Edge]

Yeah, no, I always kind of get those experiments a little confused, but I think that's how I understood it too, that the Flambeau really focused in on some detail work and those processes, as you say. And then the moss experiment, which was a really big, ambitious project replicated in three different areas of the state was, yeah, as you said, more operational. How could we integrate economics together with emulating old growth characteristics in those forests?

So two really interesting experiments and kind of really cool that you kind of got in on the ground level with your PhD work.

[Brad Hutnik]

Was there, and I'm just curious because I know moss is ongoing, you know, we'll be talking about moss, you know, when we're sitting in the nursing home. Well, hopefully, right. Hopefully.

[Greg Edge]

Well, you will be. 

[Brad Hutnik]

Yeah. Okay.

So, but, but, but that Flambeau experiment, were there any like big things that came out of that or things that said, oh, you know, kind of things that maybe led to moss or, or anything?

[Julia Burton]

Yeah, there were a lot of, I can't boil it down to one key lesson because there were so many studies, right. And it was really a big collaborative multi-investigator interdisciplinary experiment. So there was everything from ecosystem scale studies of net primary productivity and carbon storage and carbon dynamics and, you know, soil flux and coarse woody debris flux to sapling recruitment.

My studies focused on the ground layer. There's also a lot of work that came later on soil microbial communities, particularly in relation to the wood addition experiments. And, you know, really all of that was overseen by not only the PIs, but Jody Forrester, who's a professor at North Carolina State University now, really had a hand in all of those studies.

[Greg Edge]

In that experiment, did it emulate different types of, well, what we would say, horizontal structure or gaps within that? Cause I know like, I believe Craig Lorimer's work looked at, there were all different size gaps within the Northern hardwood old growth systems of different levels of disturbance. So did the Flambeau experiment try to emulate those different sizes?

What, what did we know about that?

[Julia Burton]

Right. So John Goodburn did the comparative studies of old growth and found the range of gap sizes that we used in the Flambeau emulated that range that we saw that John Goodburn measured it in during phase one. So, gosh, I always thought of those in terms of area in square meters.

And now I like, I want to be like, oh yeah, it's a 10th acre gap in a quarter. It's probably like comparing, you know, an individual tree gap to a 10, it's about 10th acre and then a quarter acre is about the range, but I haven't checked.

[Greg Edge]

That's how we always as foresters, right, Brad? We always think of those in kind of like 10th acre increments or something. Oh, we're going to make a single tree gap.

We're going to make a 10th. We're going to do a quarter. We're going to do a half.

[Julia Burton]

But that's about the range that we were, we're looking at.

[Greg Edge]

Okay.

[Julia Burton]

Which is still a pretty narrow range, all things considered, and especially when you look at some of the recommendations today, but that was reflecting the range that was measured and observed in old growth, and it's a much bigger range than you would see in the single tree selection system, for example, where you have much smaller trees. You're just removing individual trees. They make smaller openings that fill really quickly.

[Greg Edge]

Yeah. Maybe we didn't state it in the beginning, but we should be clear that we're talking about northern hardwood stands within this Lake States region, so northern hardwoods and hemlock hardwood types. I know probably those disturbance patterns in, say, your pine systems that you've been looking at look much different.

[Julia Burton]

For sure.

[Greg Edge]

Yeah.

[Brad Hutnik]

So I'm curious, you said you were focused, and it's kind of cool. You were kind of focused in on the plants. Were there some take-homes from the Flambeau experiment, like what was happening with the plants in these treatments or the understory?

[Julia Burton]

Yeah. So starting with phase one, the comparative studies, and Rob Scheller led that work, you could see that the composition of the understory community was associated with those gradients in light and coarse woody debris that distinguished old growth from managed forests, and my research in phase two highlighted that in the absence of gaps, plant communities really organized along different edaphic gradients that were associated with soil texture, as well as the composition of the overstory. So hemlock had an influence on the composition of the ground layer, for example. There was also some dispersal limitation.

These plants have all different kinds of characteristics. I think I had about 200 species in my quadrats, which is, you know, 10 times as many as you would have in the overstory, and so they just differ in all these different ways, including dispersal. So we also detected some dispersal limitation along those gradients.

And then after the gaps were created, you could see different community compositions in the different gap sizes, which suggests that that range of gap sizes was or is really important to maintaining diversity within the forest.

[Greg Edge]

Do you think those understory plant communities are resilient to that disturbance? So we make, obviously, disturbance and gaps in these forests all the time, and I've wondered about, like, how are we impacting those understory plant communities? Do they bounce back or change when those, say, those gaps close?

Or, like, how resilient are those?

[Julia Burton]

Yeah, that's a good question, and the answer is probably pretty complicated. What we see when we compare the younger second-growth stands to the old growth is that diversity metrics like species richness and other diversity metrics, it's hard to show a difference. The understory looks really resilient, considering these stands were clear-cut.

There were maybe some slash fires, and yet these communities that are really dispersal-limited, these species that are really sensitive, seem to recover. But there are subtle differences in composition related to that removal of coarse woody debris, and then those changes can be more persistent in stands that are managed regularly with frequent entries that, you know, maintain higher light and more homogeneous light conditions over time. So that, I think, can have a more persistent effect.

[Greg Edge]

So, Julia, are you saying some of those plants are linked to that coarse woody debris? Like, because that coarse woody debris was, say, decreased in those second-growth stands, there are some plants that relied upon that?

[Julia Burton]

Yeah, the analyses from Rob Scheller's work in phase one certainly suggest that. They certainly show that correlation between species composition and the coarse woody debris. And what I see in that is that at these sites kind of near Sylvania and Watersmeet, the old-growth forests with more coarse woody debris tend to have more like a podium species, whereas the second-growth forests with less coarse woody debris tend to have more graminoid grasses and sedges.

So that's what it appears in a correlative study. But we need the experiments to kind of confirm that over time.

[Brad Hutnik]

Were you able to tease out impacts of deer with the understory? Because I know, like, if you're creating those different size openings, that could have changes or maybe impacts on deer habitat and maybe use of the forest.

[Julia Burton]

Yeah, we did have gaps with and without deer exclosures. And where we had deer exclosures, the effects of gaps on heterogeneity, community heterogeneity, were more pronounced. And what the deer tended to do where they weren't excluded was eat the forbs.

And that kind of freed up resources and growing space and allowed the grasses and sedges to become relatively more abundant. And they also would pick out, you know, the more desirable tree species or palatable tree species. If there was a single yellow birch, they seemed to find it.

[Greg Edge]

And that's kind of the rub, right? Like what we're seeing in so many different places where the sedge is becoming more dominant as opposed to the forbs and the tree regeneration less abundant.

[Julia Burton]

Yeah.

[Greg Edge]

You know, have our deer populations now, like, fundamentally changed those dynamics that would have happened in these northern hardwood stands?

[Julia Burton]

I think it's a really interesting and important question. And I think we need longer term studies to really follow that over time. And the answer probably varies with both deer density as well as site quality.

And this was a really rich site, or is a really rich site, really silty loam, you know, really high on the, on the cotar gradient moisture and nutrient. And we still saw the impacts. And it was intermediate, kind of intermediate deer densities and a rich site.

And we still see kind of subtle but important effects of deer. Whereas on other sites, for example, on the counties that border Wisconsin, we have huge high density deer issues. And they eat all the, they eat everything.

They eat all the sugar maple. And we have terrible regeneration failures.

[Brad Hutnik]

You know, it's interesting. And this makes me wonder about even history of some of these sites, especially in northern Wisconsin or the UP, because, you know, we went through that phase of very young stands, or even before that, much higher deer populations than we have right now. And wondering if we're seeing some legacy impacts of those long-term deer from the past, maybe now we're seeing the impact.

It's not necessarily the deer we, it's partly the deer we have now, but it's maybe a big chunk on the deer we've had historically.

[Julia Burton]

Right. Yeah, the Flambeau, you know, Autumn Sabo followed up on my studies to look at longer term effects after seven years. So I looked at the first four years, three or four years.

And she was seeing these really stunted tree seedlings that were almost like bonsais because the deer had repeatedly browsed them. So you'd have like these bonsai-ed American elms. And will those trees ever grow in a gap?

Will they ever recover? I don't know. But that speaks to that legacy.

[Greg Edge]

Yeah. So many of these things, as you said, Julia, we have to study more longer term because there's so much variability in what's happening there. And that legacy effect, as you said, Brad, just makes it more complicated.

So what you're seeing today, is it because of today's browse impacts or past?

[Brad Hutnik]

I think the corollary is here in Southern Wisconsin, we had a history of grazing in our forests. And so when we don't see some of the plants we expect now, we kind of have to go back and say, was it the cows that took them away or is it the deer now? And we don't know.

I mean, in some situations we do, but in very many, we just have questions.

[Greg Edge]

Season 7 of Silvicast was made possible thanks to sponsors like the Family Forest Carbon Program. The Family Forest Carbon Program pays landowners to improve the health of their land and increase the long-term value of their property. The program equips landowners with the resources and support to implement sustainable practices that help them reach their own goals for their woodlands, while also improving the health of their forests and our planet.

To learn more about how you can access these benefits for your forest, visit familyforestcarbon.org. Julia, we touched a little bit on the issue of deadwood and coarse woody debris. But I think I'd like to kind of just circle back to that just a little bit, because I think it's a really important issue.

And one thing that I always took away from Craig Lorimer's original work looking at the old-growth stands and the second-growth stands was that really big difference in that deadwood component. And can you speak to a little bit about that between what we're seeing in that old-growth original forest and what we see in our typical second-growth northern hardwood stands?

[Julia Burton]

Yeah, we see that the second-growth stands and managed stands, stands managed with the selection system, have a lot less coarse woody debris, and particularly in the larger size classes. So bigger logs and more kind of intermediate and advanced stages of decay, right? Those younger stands, they're going to be, you know, just coming out of the self-thinning phase.

So there might be a lot of snags and a lot of pieces of wood on the floor, but they're smaller trees that are dying as the stand goes through stem exclusion. And those larger pieces of coarse woody debris and larger snags are really what's more ecologically important, right?

[Greg Edge]

And I know on, too, I think what we saw in the moss study, right, was where we manage stands, the standing dead, the snags tend to get eliminated and knocked down for whether that's safety reasons or whether that's just simply, you know, being knocked down during the removal process. So that's having an impact on that deadwood component as well.

[Julia Burton]

Right. Just unintended consequence of operations.

[Brad Hutnik]

I'd be remiss if I didn't ask about this. Is there any relationship of fire in these systems at all? Like, it seems like, you know, where you were, it was really, like when I think of the Flambeau, I should bring rubber boots.

But, you know, sometimes fire still played a role in those places. Has there been any work on fire as a part of old growth in these systems?

[Julia Burton]

Yeah. So some of the foundational work of Craig Lorimer and Lee Frelich from the Porcupine Mountains reconstructed a disturbance history. They had limited capacity to look at, like, light severity and moderate severity fire because sugar maple trees and hemlock trees aren't good at recording fire scars and maintaining them.

But they did find that the return intervals and rotation periods for severe fire and severe wind were extremely, extremely large and long. And rather that the disturbance regime is characterized by light to moderate severity wind throw. But I would say there are still some gaps in our knowledge in terms of, like, how important was light and moderate severity fire, like just surface fires that go through and skunk around and kill off the advanced regeneration.

[Greg Edge]

Yeah, we talk about that sometimes, Brad. Like in Wisconsin here, we have, like, a landscape that's this big matrix of forest types. And we know in some of those that that low severity fire was quite common.

And it's only logical that it skunked around into the northern hardwoods too at times. 

[Brad Hutnik]

That's our technical silvicultural term for the day, skunked around.

[Julia Burton]

I can just envision it. The skunk tail’s like a little flame.

[Brad Hutnik]

But I always have this feeling, like, someday we're going to be talking about this and people will accept it as just like, oh, yeah, we knew this all along and we're living in that age where it's like, we don't know. Or coming from an age where it was like, no, they never burned kind of thing.

[Greg Edge]

So Julia, you're currently involved in an effort to resample, I don't know, some or many of those original old growth plots in places like Sylvania, Porcupine Mountains. You mentioned Duke’s Experimental Forest. So what are you hoping to learn by going back and looking at those plots again?

[Julia Burton]

Yeah, I guess you could kind of think of it, well, maybe we're launching phase three, right? What we're really interested in, you kind of see all of Craig Lorimer's body of work coming from the Porkies, starting with establishing or reconstructing that disturbance regime and then kind of using all these studies to parameterize the canopy model and kind of run these different simulations and, you know, use his crystal ball to look at kind of simulation experiments. And that kind of provides a baseline for what we understand about the dynamics of these forests historically.

But as the climate changes, as deer are having more and more effects on the forest, invasive species like emerald ash borer, earthworms and plants, and then climate change where we have warmer summers, longer growing seasons, more variable precipitation, shorter winters. How is this going to affect old growth forests now and in the future? So we have really great records from the previous work that's been done on these systems by Craig and his students, Lee Frelich, Margaret Davis, Kerry Woods, and Crystal Kearns and others who have worked at the Dukes Experimental Forest and Research Natural Area, where we can look at, you know, are we seeing a signal where demographic rates of growth, mortality, and recruitment are changing over time? Does it vary among species? And how does this scale up to affect productivity, diversity, and carbon storage in old growth forests?

And then we can also use that as a reference for looking at managed systems. So we often think of those old growth forests as being more resilient. There's more heterogeneity, diversity in age structure, species.

And so we can look at that. Are they indeed more resilient? Is emulating these processes and patterns in managed systems, is that sufficient?

For maintaining resilience and managed systems? Or do we need to go further and think about assisted migration and other options?

[Brad Hutnik]

When you talk about resilience in a system, it makes you think about, you know, so they were able to take the punches in the past, right? And keep going. They didn't change.

And so if I'm reading this right, would you say that old growth systems, at least the looked at, would be more resilient for climate change than some of the, like, maybe simpler systems that we've produced? The second growth stands that we've managed in a different way than what we had historic, or what produced our old growth stands?

[Julia Burton]

Yeah, I think that is an exciting hypothesis. I think there are alternative hypotheses. And yeah, that is one hypothesis you could make the case for, right?

There's these really old trees that have stood the test of time. They have the genetics that can tolerate the variability. There's this, they moderate the microclimate.

And so things are cooler in the understory, higher relative humidity and buffered. So yeah, I think that's one hypothesis. The other hypothesis is that, you know, there's going to be some demographic inertia.

And the disturbance is in, the disturbance regime doesn't permit the right species to get in that are going to be better adapted. So we need to kind of help the forest out by moving with assisted migration plantings, by moving species that are going to be better adapted.

[Greg Edge]

And I guess that's how you get to it is what you're saying is monitoring these things long term to see if there are shifts between the old growth forest and the second growth forest relative to that climate change and those other factors like deer that are now different in the picture.

[Julia Burton]

Yeah, so kind of we can zoom in and look at like the fine scale processes of growth, mortality, recruitment. And then we can also zoom out and we can see if, you know, we can pick out those that would maybe eventually result in declines in productivity. And we can also zoom out and look at, you know, over time while productivity is pretty stable and the forest is continuing to provide all the values and services that society depends on.

[Greg Edge]

So Julia, we've kind of covered a gamut of work from Craig Lorimer's and Dave Mladenoff's to yours. Are there any other really sort of important differences that that work and your work has seen between these old growth and managed forests that foresters should think about or consider?

[Julia Burton]

Yeah, I kind of think of maybe three or four key take homes from especially the body of Craig's and as well as my research. One, you know, we often look at like the Oliver-Larson model that's a linear progression of stand development. So the reconstructed disturbance regime suggests that rather than that stand dynamics were followed multiple pathways of development, there's, you know, more diverse age structures and disturbance could move stands forward with and stand development along those pathways or backwards.

So there's multiple pathways. So disturbance accelerated and set back stand development towards old growth. And moderate severity disturbances were really important.

And that's what accounts for that, you know, that range of gap sizes in the overstory. So it wasn't just, you know, either we have catastrophic disturbances that set things back all the way to time zero or single tree disturbances that maintain a stable balanced structure. And that's really important because it gives managers a much bigger space to work, more options, not just one or the other.

And another part of that is that these balanced all age stands that we tend to develop our target structures based on were really uncommon. So because of these, these moderate severities created kind of lumpy multi-cohort distributions rather than a balanced all age distribution where each age class occupied the same amount of area. So I think of those as like really important messages for managers who want to kind of use ecological silviculture and developmental models.

You're not as constrained as maybe we thought we were with that, you know, reverse J or rotated sigmoid or negative exponential target structure. If I'm on my soapbox with that, another big contribution related to that is that those distributions, if we are shooting for that stable distribution, which there are good reasons to do it, right? If we're, we want to sustain yields at an individual stand scale is that the force can be like really deceptive, especially northern hardwoods in that that diameter distribution can look stable.

It can resemble negative exponential, reverse J, rotated sigmoid, whatever your favorite stable distribution is when you're planting all trees. But because these trees can grow in the shade of their neighbors, they might be the same age. So they might just be one big spread out cohort that looks like an uneven age stand with a reverse J.

So it's really important to, you know, look at those diameter distributions by crown class, omitting the suppressed trees to discern whether that stand really is even aged or uneven aged because, you know, it's like a cardinal sin to apply the selection system to an even age stand. I see Brad nodding, so I'm not alone here.

[Greg Edge]

I mean, and that's always been the big trick, right? It's determining, we use those diameter distributions as a surrogate for age. But as you said, Julie, it's not always the case.

And it's sometimes tough to tell in those stands. We've talked some about this in past topics about telling whether those are actually uneven age stands or not. I think, as you said, kind of that conclusion from all that body of work that there were these range of disturbances that kept these systems in play, as you said, really opens up the door and flexibility for foresters to maybe manage under different systems than just traditional single tree selection.

Although that's a perfectly, if that fits the objective, that's perfectly fine.

[Brad Hutnik]

Feels to me like based on some of this that, you know, historically, we haven't thought about area-based management in northern hardwoods. But if we're thinking about those gaps as the driver of development, you know, the gap in single tree was really kind of that merchantable target and then kind of pseudo creating those conditions for the regeneration. But it sounds like we could expand that silvicultural box for what we're working in in northern hardwoods and think about some of these other systems maybe we haven't used as much.

And especially with thinking about things like maybe mimicking old growth.

[Julia Burton]

Right. And I think that was part of the idea for the moss, right? Because like the moss combines shelterwoods and single tree and group to get all the heterogeneity, right?

[Greg Edge]

Yeah. That study is designed to be a 50-year study. And we're actually only in year 15, I think, of collecting the data on that.

And they're working on analyzing some of that. So really the early stages of it. But yeah, that's the whole gist of that was trying to say, how could we manage these second growth stands to get some of those characteristics?

And I guess I'll ask you that, Julia, like, what do you think maybe are a few takeaways from all of this work? I know we just talked about one, but that foresters could do to maybe manage all of these second growth stands that we're dealing with, but maybe emulate some of those better characteristics that you're seeing in the old growth stands.

[Julia Burton]

Yeah. So I mean, thinking a lot about that coarse woody debris and the snags and doing some legacy retention. So you can tweak your arbogast target to have no maximum diameter or retain one tree of the largest diameter in the largest diameter class per acre and just let those trees grow and die and recruit to the coarse woody debris over time.

Also retention patches. So we often think about the managed forests as kind of lacking the bigger gaps, but they also lack that deep shade of the old growth. So we want to not only incorporate gaps of different sizes, but also maybe have some retention patches to maintain that really deep shade.

You could create snags. Another thing that we haven't talked about yet is that, and the findings are a little bit mixed, but in Minnesota and when I look back at John Goodburn's data, what I see is that the second growth stands have fewer, less diversity in the overstory. So less yellow birch, less hemlock, and conifers overall.

So thinking about trying to restore that conifer component, and of course we have to protect them from deer if we're doing any planting. We have the NH seed experiment up here where we did all these alternative silvicultural overstory regeneration treatments and found that they really didn't increase diversity unless we had direct seeding and deer exclusion in conjunction with them. So the deer are a big problem and unfortunately an expensive problem for us.

[Greg Edge]

Yeah, we haven't talked about deer problems at all, have we Brad?

[Brad Hutnik]

No, and actually I think our listeners playing the Silvicast drinking game at home will be happy that we've mentioned deer numerous times during this episode. So we're helping them. You know, it feels to me like, you know, hearing about your experience Julia and just those take-homes that there's kind of a little bit of humility that foresters are going to have to take with some of this, where I think maybe we had some ideas about what we knew, but we just have to keep an open mind to maybe some of these things as we go forward because it feels like we're going to keep learning things about this for quite some time.

[Julia Burton]

Yeah, we're going to keep studying it. We think it's important. You know, different landownerships might look at some of these things as a bigger investment than they're prepared to make, but I think what we're going to learn over time is that these things are going to become more and more important for maintaining the basic functions and values that northern hardwoods provide on all landownerships.

[Greg Edge]

And I think too, and we've talked a little bit with Paul Catanzaro in the past about emulating some of these characteristics, what I hear is there's quite a bit of flexibility in terms of maybe adding some of these components you just listed to lots of different management schemes, you know, and whether that's just, as you said, retaining some larger size classes in perpetuity within that stand. I like the idea of some of the dense patches within that, so the deep, you know, keeping the deep shade, we don't often talk about that component of it. And also, you know, that impacts, as you said, on the understory plant community as well, as foresters often looking up.

So it just seems like a lot of these components could be integrated to some degree, depending on your goals, into lots of silvicultural systems that we're managing in these stands.

[Julia Burton]

Right. If we can link it to resilience and climate change adaptation, you know, that's a, anyone in the Sustainable Forestry Initiative program, you know, has to address it. So these are some of the tools that we have for addressing resilience and climate change adaptation overall.

[Greg Edge]

Well, and I'll be really interested as you monitor these plots long term, sort of that your hypothesis, the two alternating hypotheses in terms of what will do best and what we can start to integrate into these vast acreages of second-growth stands to get more of that resilience that we want. And, you know, are we going to need to go to assisted migration or can we tweak it with different, you know, different, maybe smaller treatments to really just increase that resilience? So it'll be really interesting to see what we learn as we go along.

[Brad Hutnik]

And we haven't even talked about the financial aspects of any of this today. But in a way, I could see if you're resilient, you may be resilient financially as well, as opposed to, you know, maybe having the hiccups that would come with trying to manage in an uncertain future. So I guess there's a lot more to come on this stuff.

This is kind of exciting.

[Greg Edge]

So thanks, Julia, for just coming to discuss with us today. Folks out there don't know, but you touched on it earlier. You are working in lots of different areas.

So I know you and I have had lots of discussions of trying to look at some of these old forest structures and dynamics in other forest systems across the Lake State. So look forward to, you know, lots of more discussions on this topic in the future.

[Julia Burton]

Likewise.

[Brad Hutnik]

We're always glad to have Michigan Tech as our third state school here in Wisconsin. We claim you guys, whether you like it or not. So.

[Julia Burton]

Well, thanks so much.

[Greg Edge]

Thanks, Julia. Bye-bye. Brad, that was a great conversation with Julia. It was.

She brought up a couple of terms. So I think maybe this is a good time for Silvictionary.

*silvictionary theme song plays*

[Brad Hutnik]

I'm still going to say ride the Silvisaurus, my friend.

*dinosaur roar sound effect*

[Greg Edge]

And then we got the sound effects.

[Brad Hutnik]

Yeah. Well, you know, if it were NPR, we'd make it a good sound effect. But maybe, no, no, we do have really good sound effects.

We do have really good sound effects.

[Greg Edge]

So the two terms that Julia brought up that maybe are not common lingo in our circle, rotated sigmoid and reverse J diameter distributions. What is the difference between those?

[Brad Hutnik]

So it's interesting. And I had to think about, you know, that rotated sigmoid. Greg, actually, it's a medical term.

You know, when you rotate your sigmoid.

[Greg Edge]

I don't want to. 

[Brad Hutnik]

It really hurts. You got to get some meds for it. And it can be really hard.

[Greg Edge]

But, you know. I do not want to discuss your upcoming colonoscopy.

[Brad Hutnik]

Yeah. All right. So it is now.

Okay. So it's not related to that. But okay.

But it is kind of curious. So that so, you know, we all know about that reverse J. And so that it kind of we and we've, we've seen like those Q factors that, you know, quotient of diminution, right?

So we, we kind of see this curve that kind of comes in a rotated sigmoid. And at least the best of my knowledge is something where we kind of get a plateau or bump in the middle of that diameter range. And so it's not consistent all the way through.

And so you could think of it as maybe like, like that Q, if you have a Q factor, it's not going to be consistent all the way through it. So you have some kind of a bump in it, which can be reflected in certain more distributions we see in maybe old growth stands or other stands that have maybe subject to more periodic disturbances, or maybe a, you know, something that's not as consistent as what we see in the, in like a reverse J. 

[Greg Edge]

Okay. So the reverse J has this nice decreasing diameter distribution with lots of small trays and fewer and fewer larger trays age classes, if that's related. And then this rotated sigmoid you're saying is reflective of maybe some of these uneven age old growth stands, and it doesn't maybe have that steep curve.

It doesn't have as maybe many small diameter trees, but it has this sort of plateau or bump in those middle age or sizes that's kind of drawn out.

[Brad Hutnik]

Right. And I think it could be, it could be due to a number of factors, you know, because, and this may be more reflective of natural stands as opposed to managed stands where, where we've tried to get that reverse J in the past. In natural stands, we may, and I think from some of the literature, it basically shows that bump might be a little more, that might be more natural than what we would find with the reverse J.

So the reverse J is a little bit artificial. We're imposing it versus some of these other ones that, that rotated sigmoid may be a little closer to what we might have expected to see historically.

[Greg Edge]

Could I try to manage to this type of diameter distribution if I wanted to emulate? This old growth, uneven aged condition?

[Brad Hutnik]

I think you could. And in fact, we were just reading about, I think if people are interested in the SAF, one of their newsletters recently, William Keaton talked about some old growth work they've been doing in the Northeast where they did use a diameter distribution based on something like that, a rotated sigmoid. And so I think that's, that's possible.

It's just one of, it's one more way of approaching it, kind of using that diameter distribution as opposed to say, like sizes of the disturbance gaps or things like that.

[Greg Edge]

Interesting.

[Brad Hutnik]

 Yeah. And it's really cool.

And it's not one of those terms we use on a regular basis. So it's, but I think it's just something to be familiar with, which is really good. So, hey, by the way, not completely unrelated to those.

Our conversation today made me think of two resources that, that our listeners might be really interested in, and both of them are fairly new. So Paul Catanzaro and, and Anthony D'Amato recently put out a guide, Restoring Old Growth Characteristics to New England's and New York's Forests, which could have application. So it's basically, you know, based on the experience of the Northeast, but I don't see a reason why if we were using different targets, you could use those same things or the same principles from that guide here in the upper Midwest or other places.

So I think that's something for everybody to explore. And at the same time, they've also come out recently with a book called Tending Your Forest: A Guide to Ecological Forest Stewardship in the Eastern and Central United States. I think both of them would be really good places if people are interested in old growth or natural disturbance or things like that.

I think these are really good resources for people to, or for foresters to start exploring if they're thinking more about this. 

[Greg Edge]

Cool. 

[Brad Hutnik]

So if you're interested in these resources, we'll have links and more information available about them in our show notes.

Thanks for listening to today's episode of Silvicast. If you have ideas for future episodes or a question for the Dropbox, please let us know. You can reach us at UW-Stevens Point's Wisconsin Forestry Center by emailing wfc at uwsp.edu. And feel free to include a sound file of your question or your comment if you like. Remember, we learn best when we wrestle with questions, so please keep them coming.

[Greg Edge]

And take care, everyone. And as always, thanks to our team. Susan Barrett, Editor-in-Chief.

Joe Rogers, our IT Master. Theme music by Paul Frater. And of course, UW-Stevens Point's Wisconsin Forestry Center.