Forest Transformation in the Southwest

Impacts from rapid climate change are challenging traditional land & wildlife management strategies that were based on a stable baseline condition. In some locations we are already observing early-stage ecosystem reorganization in response to historic land management practices combined with recent novel climate stresses. Dr. Craig Allen and Dr. Nate Stephenson discuss how the convergence of climate stress, human land use patterns and histories, and disturbance trends in the southwestern United States are leading to forest ecosystem changes and transformation. Image source: Pixabay.

Papers mentioned during the interview:

Allen, C.D., Macalady, A.K., Chenchouni, H., Bachelet, D., McDowell, N., Vennetier, M., Kitzberger, T., Rigling, A., Breshears, D.D., Hogg, E.T. and Gonzalez, P., 2010. A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests. Forest ecology and management, 259(4), pp.660-684.

Janzen, D., 1998. Gardenification of wildland nature and the human footprint. Science, 279(5355), pp.1312-1313.

Millar, C.I., Stephenson, N.L. and Stephens, S.L., 2007. Climate change and forests of the future: managing in the face of uncertainty. Ecological applications, 17(8), pp.2145-2151.

Milly, P.C., Betancourt, J., Falkenmark, M., Hirsch, R.M., Kundzewicz, Z.W., Lettenmaier, D.P. and Stouffer, R.J., 2008. Stationarity is dead: whither water management?. Science, 319(5863), pp.573-574.

Bioscience. January 2022 Issue (RAD spotlight)

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Transcript

[00:00:00] Emile Elias: Welcome to Come Rain or Shine podcast of the USDA Southwest Climate Hub 

[00:00:05] Sarah LeRoy: and the USGS Southwest Climate Adaptation Science Center or Southwest CASC. I'm Sarah LeRoy science applications and communications coordinator for the Southwest CASC. 

[00:00:17] Emile Elias: And I'm Emile Elias, director of the Southwest Climate Hub.

Here, we highlight stories to share the most recent advances in climate science, weather and climate adaptation and innovative practices to support resilient landscapes and communities. We believe that sharing some of the most innovative forward thinking and creative climate science and adaptation will strengthen our collective ability to respond to even the most challenging impacts of climate change in one of the hottest and driest regions of the world.

The contents of this podcast are for informational purposes only and should not be interpreted as endorsement for any of the products, technologies, or strategies discussed.

Today we are joined by two experts in ecosystem transformation, both recently retired research ecologists with the USGS who have lived and worked in two different Southwest US landscapes for the last 40 years, co-located with land managers. Dr. Craig Allen is based out of Bandelier National Monument in the Jemez mountains of Northern New Mexico.

And Dr. Nate Stephenson is based at Sequoia National Park in the southern Sierra Nevada of California. During the past few decades, extended droughts, massive floods, intense hurricanes and catastrophic wildfires have been occurring with increasing intensity and frequency. The impacts from rapid climate change are challenging traditional management strategies that were based on a stable baseline condition.

Compounding this is the intersection of climate change with 20th century land use legacies. In some locations, we are already observing early stage ecosystem reorganization in response to historic land management practices combined with recent novel climate stresses. Today we'll be discussing how the convergence of climate stress, human land use patterns and histories, and disturbance trends in the Southwestern United States are leading to forest ecosystem changes and transformation. We'll also discuss some tools that managers have available to them to deal with these changes. 

Welcome Craig and Nate. It's so good to have you both with us today. We'd like to begin with giving our listeners just a description of ecosystem transformation. What does ecosystem transformation mean? And what does it look like in practical terms in the west?

So we'll start with you, Nate. 

[00:03:01] Nate Stephenson: Yeah, I'll start with what might be a dry technical definition, and then make it concrete. For me, ecosystem transformation is something like substantial directional change in the structure, composition or function of ecosystems. 

And by directional change, I mean, it's a change that happens. And it's not likely to go back to its previous state for the foreseeable future. If, on any time scale that we can imagine. To make it concrete, I think of, since I'm a forest ecologist, I think of forests getting converted to shrublands or shrublands getting converted to grasslands. 

But it doesn't have to even be that dramatic. It can be more subtle. You can still have a forest, but you've lost some species from it. And perhaps even gained some species from outside that forest, have come in.

[00:03:54] Sarah LeRoy: Thanks Nate! Craig, do you have anything to add?

[00:03:57] Craig Allen: Yeah. Would amplify what Nate just said in as much as, ecosystem transformation can be slow and very gradual, or it can be incremental in little pulses, or it can be literally overnight transformational at times when it's disturbance mediated, disturbance from an ecological standpoint, being processes like fire, floods, insect outbreaks. So some of those there's different timeframes with it. So associated with that magnitude of transformation, there's also a timescale that's highly variable. And so in reality, ecosystems are always in flux. They're not static in, you know, either in terms of patterns or processes, they're always varying through time.

But when we started our careers back in the day, few decades ago, there was a lot of discussion about the historic range of variability. That systems they, there was oscillation, but it was within a bounded kind of range. Some of that was based on what we had observations of and knowledge of. As we get deep time knowledge through things like pollen and charcoal and more of that, we can see there was a lot of change back through, through time, but we're living in a particularly rapid period of ecosystem change and transformation now. 

[00:05:24] Sarah LeRoy: Speaking of that rapid transformation, Craig, could you maybe explain some of the kinds of threats that ecosystems are facing in the Southwest as the climate warms? 

[00:05:35] Craig Allen: Yeah, well, based here in, in the monsoonal part of the Southwest, Arizona, New Mexico, we get summer monsoonal rains.

Now we're seeing a hotter drought. We've been in sort of emergent megadrought for going on more than 20 years now, since about 2000 it's been pretty persistent, which is more a failure of the, or a reduction in the winter precip. We're living through one of those dry winters right now, and then the warming.

So in terms of, again, forests. Like Nate, I'm a forest ecologist and that's been some of the most visually dramatic changes that, that most people have noticed is trees dying directly from drought and heat stress, from big insect outbreaks, particularly including bark beetles, that affecting different tree species and then increasingly large and severe wildfires.

And all of these have really ramped up the amount of tree mortality that has gone on in the last twenty, twenty-five years. And these landscapes literally look and feel differently now than they did in the mid-nineties and late nineties, when this really started to ramp up regionally here. 

[00:06:57] Emile Elias: Craig, to expand on that a little bit, you authored a global assessment of tree mortality due to drought and heat stress.

And so I'm wondering what the biggest takeaways were from that assessment. You were the lead author on it. I know there were many coauthors and we were just talking about the Jemez mountains and what you've seen there, but what did you take away from that global assessment? 

[00:07:20] Craig Allen: The most striking thing is that there are already examples of drought and heat induced tree mortality, outside the historical norms that we have records of in every major forest type on planet earth. So we're seeing all forest types on the planet are already vulnerable. Can't determine yet, you know, whether the pace to that is really picking up globally, but it certainly is in some regions. And so anyway, all major biomes are already vulnerable forested systems.

The second big thing is that there are major information gaps and scientific uncertainties that constrain us from being able to realistically project the fate of forests on planet earth. We're navigating a bit blind collectively in terms of even if the climate models were a hundred percent accurate, we do not have realistic models of forest stress and tree mortality moving forward globally yet. People are working hard on that. This is a major, major research frontier, trying to better project forest health and mortality moving forward. 

Related to that, and something that would help in that effort, is we need a global observation system, in near real time and across the planet of changes in forest health and mortality. You might think, you know, global satellite remote sensing can do that. And it's, it can sort of do parts of that, but not well enough yet. And it needs to be combined and coordinated with, with ground observations. So that's another thing that's still in early stages.

And then the last thing I would just say since then, it wasn't part of that 2010 paper and Nate will have something more to say about this, I think, but there's evidence that big old trees on planet earth, not always, but often are, are more vulnerable to hotter drought on this planet. And in any case, big old trees on this planet are taking big hits and there is concern about how long they will persist moving forward here in coming decades.

And they provide, there's a lot of unique things associated with the ancient, iconic mega flora of planet earth, which are trees, big trees, big old trees. And so this is something that both of us think about a fair amount. 

[00:09:50] Emile Elias: You’ve said a few things I want to ask a lot more about and potential for this developing global monitoring network that includes ground-based observations. And also what's happening to our big old trees. We will circle back to those topics and talk a bit more about them. Now I have questions to bring it back to our local landscape because many of the changes that we're seeing and especially the adaptations that we're taking occur at the local level, and you both work in mountain forest landscapes in the Southwest.

Are you seeing transformations in these forests? And if so, what are you seeing? And we'll go ahead and go with Nate first. 

[00:10:33] Nate Stephenson: Yeah, I'll start back in the beginning of my career here. When I first started working in the southern Sierra Nevada in 1979, I had heard about climatic change in graduate school, and knew that that was a possibility we could be facing, but it was a very abstract thing.

It wasn't until 1990 that we actually started climate change related research here, but we still couldn't even tell if the temperature was actually going up. I'm actually going somewhere with this. We started the monitoring we would need to be able to detect changes in forests if the temperature did start to go up and then by the early to mid 2000s, we were actually seeing changes that we could attribute to a warming climate with a fair bit of confidence, not complete confidence. So we, we had this forest monitoring network that we had set up to be able to detect changes if they came and by the mid 2000s, we were actually seeing those changes happen. But they were extremely subtle. You had to be looking really hard.

And when we first analyzed the data that said tree death rates are going up, we didn't even believe our own results because it isn't something we had noticed happening when we just walked through the forest, you had to be monitoring very carefully to see it. But we, we tried to make the result go away and it wouldn't go away, and we finally decided it must be real. 

So I had this in my head that we were going to see changes that were going to be subtle. And, but they would add up through time. They would accrue through time, but then we get to the mid 20-teens and we get these dramatic suddenly instead of chronic background change, we're getting acute change on a, very severe change and what set it up, it was initially, what helped set it up was a hotter drought we had from 2012 through 2016. And by hotter drought, what I mean is if all you had had was a rain gauge, you would have looked at your rain gauge and said, wow, this is a severe drought, but it has a precedent.

If we go back to 1924, here, we can find a year as dry as this year. The big difference was it was a lot warmer. And that warmth means the evaporative power of the atmosphere increases. So, you know, the demand side of drought had increased. There's a supply side and a demand side, and that pushed a whole bunch of trees over the edge through bark beetle outbreaks mainly.

So we got a landscape suddenly that had just wall-to-wall dead trees on it and then came the wildfires because you suddenly had so many more fuels on the ground and they were at record dry conditions that you got wildfires of a severity that no one had ever seen before in these areas. And I forget your question. Did I answer it? 

[00:13:43] Emile Elias: You did. And I have the same question for Craig. Craig, you're in the forests in the mountains of Northern New Mexico. And you mentioned some of the things that you're seeing there, including drought. And I wonder if you want to expand on those or if you're seeing any other impacts you'd like to talk about.

[00:14:01] Craig Allen: Yeah, well, again, in the 40 plus years that I've been working specifically say in the Jemez mountains landscape here in Northern New Mexico. That first summer of fieldwork, summer of ‘81, the Southwest US was a great place to be a tree. That whole window from ‘78 to ‘95 was a window, when you look at the long tree ring records, that was in Arizona, New Mexico, maybe the best window for tree growth in the last thousand years. And abundant winter snow packs - so human societies are happy. The skiers are happy. The irrigators are happy, but, the forests were happy. In the sense of at least relative to things like tree growth, but it was being set up.

And those of us who, you know, knew a bit about sort of the dynamics, the longer dynamics of systems did worry that the next time it turned multi-year dry, the bill would come due somewhat. And the thought was a lot of, it was just because of fire suppression, right? That these forests were kind of an order of magnitude denser than they had been in 1900 when high-frequency surface fires were an important part of many of the, of the forests in this part of the world. 

So yeah, we kind of expected that, but as Nate has also related the climate change seemed theoretically, it was a thing that we expected to come, but it's one thing to, to project that conceptually, and it's another to sort of experience it. And the warmer we've, we transitioned at the very end of the nineties, by 2000 into drought, that's been persistent in this region. And with that, tree growth has been constrained. Before trees die, they, they reduce leaf area. It's one of the ways they try to deal with water shortage.

So things like conifers, evergreen trees, they put on fewer needles in the year. They don't hold their needles as long, the needles are smaller. The whole leaf area reduces, so they don't have to transpire as much. And the forest, just the whole canopy, walking, it feels different in a forest when this happens. You can literally it's, to me, it's kind of a feeling of the stress building in the system when it's incremental.

And you can feel that going on by 2000, I wish we had worked on data for that kind of thing in terms of assessing leaf area. Yeah. The forests I walk through now are not if they're even still forests. It's just is a completely different feeling in the landscape. The vistas are much better now because you see 80 miles, a hundred miles, to the next mountain range in all directions in these places.

But there's contiguous 30,000 acre patches where what was all conifer tree cover there's just a couple of little clumps of trees here and there left, but largely from the wildfires. But the same kind of progression that we had a lot of tree mortality from drought and heat stress, and then insects, bark beetles of varying species. And then starting in, literally actually the spring of ‘96, after a near snowless winter, we started to get wildfires. Suppression didn't work.

Part of the reason that periods of the ‘78 to ‘95 was fire suppression was still working in the last fire seasons, the warming hadn't been significant enough yet, ah, fire season started late because of abundant winter snow packs. And, suppression was still able to keep a lid on it, even when the fuels were out there and a lot of ecologists and fire ecologists, said eh, one of these days during droughts, this is going to be a problem. And it's been a problem. And it's been, the problem has gotten bigger and has been amplified by the warming, which dries the atmosphere, dries the live vegetation, puts water stress on the live and dead vegetation out there and ramps up the, the severity of the fire behavior. 

But literally it's almost disorienting walking through parts of this mountain range that I know better than any place on the planet, because I've spent my whole adult life here living and working and studying it. And it's used to be dense forests. And now you're walking through either very open forests or non-forests that have been converted to grasslands and shrublands.

[00:18:22] Emile Elias: So Craig, you've seen some really profound changes over the last 40 years and the ecosystems that you work in, but something stuck in my mind when, when I was listening to you talking. You said something about the forest being an order of magnitude denser. And so in my mind, I started thinking, does that mean that instead of there being one tree, there would be 10 or instead of there being 10 in a specific area, there would be even a hundred?

And so I wonder if you can kind of expand on this idea of an order of magnitude denser, what that means on the landscape. And then you've already talked a bit about the transformation, the other way, after a wildfire, where there was a very incredibly dense forest that becomes a vista or just a few trees.

Did I catch that right? Is that what you meant in terms of being an order of magnitude denser?

[00:19:18] Craig Allen: Yes. I meant literally an order of magnitude, as in tenfold, denser in the forest. And that's an overbroad generalization, you know, the ecology of vegetation on landscapes is continuously variable across the diversity of slopes, elevations, soils, landforms, but here in the Northern New Mexico, in this landscape, the largest fraction of the forests are in zones, Ponderosa pine, and dry or mixed conifer forests zones that had very high frequency, surface fires dominant prior to the very late 1800s.

Both, lot of, lots of lightning ignition here, humans are, have been part of the system here too for millennia. Those fires burning through kept the forests relatively open. They thinned out a lot of the tree regeneration during wet decades. There's a natural oscillation here. The El Niño-La Niña kind of climate pattern oscillating, right.

El Niñ's give us wetter winters here historically in Arizona and New Mexico. And La Niñas are the drier winters. But then there's this thing that climatologists have become aware of in the last 20 or so years, the Pacific Decadal Oscillation that seems during that time, decadal scales basically is modulating how frequent of El Niño and La Niñas we get.

So basically we get decades where, and as far back as we can look in the tree-ring record, we can see that their precipitation has been variable on essentially all timescales. Annual, decadal, even centennial to some extent. But this, decadal oscillation - every 50 or so years we come out of, we're, we're wet for a decade or two, and then it oscillates and it goes back and we're dry for a decade or two. Prior to this megadrought here in Southwest Arizona-New Mexico region, since about 2000, the previous one was from 1942 to ‘56. The so-called 1950s drought. During these dry periods, there's naturally some tree mortality on the dryer margins of their distribution.

There's more widespread fire activity. You got longer fire seasons, fuels are more available. During the wetter decades you get pulses of tree regeneration. When you look at things like Ponderosa pine, if you look at the demography, the age structure with tree rings, going back 400 years. There's only pulses of regeneration about twice a century pre-1900.

Okay. During those wetter decades, you get a bunch of little tree seedlings. Fire frequency, you might miss one or two surface fires, and you get a pulse of trees. But with fire suppression, first inadvertently from overgrazing and the landscape in the late 1800s, that graded into conscious fire suppression as a deliberate policy from 1910 onward, federally spearheaded by Forest Service, but essentially all agencies were part of this. 

We were able to keep fire out of this system for most of the century in most of these landscapes. And that allowed all of those little baby trees, during at least two wet pulses in the Southwest to get established and to emerge. And so we went from more like in a Ponderosa pine forest that could be quite variable from near savannas of 20 trees per acre, to denser forests of 120 trees per acre, pre 1900.

But yeah, multiply that times 10, or more in some sites. So you could have more than a thousand trees per acre. And as we were coming out of the nineties and that's just not sustainable to have that much biomass, that much leaf area. Even if you had a magic wand and could keep fire out of these systems, during the drought periods there's just not enough water around available to keep that much living biomass going. So the system squeezes back, it reduces leaf area, the mortality rates, first background, mortality rates to go up and then you get pulses of mortality from things like insect outbreaks. 

But in fact, there is no magic wand with fire. Fire does happen. And those same conditions, with more dead fuel, really increase the opportunity for high severity fires that are a hard reset on a lot of landscapes. They're a filter that not all organisms can get through. So it strongly favors certain species and certain kinds of lifeforms. Things that have seed pools that survive in the soil, things which, weedy kind of herbaceous plants that can, their populations can disperse widely and grow rapidly. Things that re-sprout. Things like grasses and resprouting shrubs. 

It disfavors, almost all the conifer species in the last, all the evergreens that we think of as you know, the historical normal dominance of most of these forest types. Not universally true. There are some conifer species lodgepole pine in places like Yellowstone are well adapted to high severity fire, but not if it becomes too frequent.

That's the concern in a place like Yellowstone is the fire frequency is going to go up. Here, both the severity is really the big difference here today. So, so yes, our forests went from on the order of say a hundred trees per acre to on the order of a thousand trees per acre in a lot of places.

Although even without wildfire, that number of live trees has been being squeezed markedly in the last 20 years by mortality, the kind of natural self thinning of those dense understory thickets, which were already happening anyway. But it has been really accelerated by, by the hotter drought over the last 20 years.

[00:25:19] Emile Elias: Thank you so much for expanding on that. We hear statistics, we read them, but actually imagining them on the landscape is something different. And so thanks for giving us a bit of that history and background. Nate, I'm wondering if you see anything similar on the Sierra or what might be similar or different, or if there's anything you'd like to add from your perspective on the Sierra?

[00:25:43] Nate Stephenson: What I would like to add is the theme of surprises and, and not pleasant surprises. I've worked throughout my career with giant sequoias and they are rock stars of persistence. They're highly fire adapted to low to moderate severity surface fires. And in the past, and in the past, I mean, during my career, You would almost never see a sequoia get killed by a fire, but you would from time to time, even in prescribed fires, you know, a sequoia's base might weaken and it might fall over.

And I still vividly remember in 1987 a wildfire, it was an area where outside of the park where there had been some logging, and so there was logging slash that had never been cleaned up. 14 big sequoias got killed in a wildfire, and that was shocking to us, but still compared to the whole population it was kind of a drop in the bucket.

Even during the hotter drought we had here from 2012 through 2016. Giant sequoias were the tree on the landscape that really hardly flinched. We had pines dying in droves. We had firs dying in droves. We even had incense cedars dying in droves. And yeah, a few extra sequoias died and we think we can attribute that indirectly to the drought, but they shrugged it off and that's how they can live to be thousands of years old. 

Then we had all those dead trees on the ground, of other species - firs, pines, and so on and got the wildfires coming through. And in 2015, there was a wildfire that killed at least a hundred big sequoias, probably a lot more, we haven't been able to count them all. 2017, there were two wildfires in sequoia groves that killed at least another hundred. And we hit the fateful year of 2020, and a really severe wildfire that, as best, you know, our best estimate is it killed 10 to 14% of the entire world's population of big sequoias all in a single wildfire.

And that was a shock. We didn't see that coming because sequoias are so resilient and so well adapted to fire. And one of the things that changed is we started to see crown fires in sequoias, where the canopy is on fire and burning. And it's going from tree to tree. That hadn't been recorded before. And those fires, those crown fires in some places have been so severe that, they burned out all of the cones in the sequoias. And so the seed source is lost. So we're, in some areas it's set up for an ecological transformation that we didn't see coming. We didn't see, expect something so big and so abrupt and so severe. And then just this last summer we had yet more severe wildfires in sequoia groves.

And another 3 to 5%, we think of the world supply of big sequoias got killed off during those. And it's not fun reporting all of that, but it drives home the point that the rules are changing. We had mental models that worked for decades on how the world around us worked for giant sequoias. And those went out the window, as Craig had said earlier, overnight. 

[00:29:21] Sarah LeRoy: Thank you Nate and thank you, Craig also, for really laying out what's happening in our western forests and the threats that we're facing in the region. And thinking about how to manage for these forest changes and transformations. You know, you mentioned that our ways of thinking have really just been thrown out the window.

And so, you know, there are lots of different methods and schools of thought, but one framework that's becoming increasingly popular is this Resist, Accept, Direct framework or, you know, better known as the RAD framework. And so Nate, I'm wondering if you could describe this framework for our listeners and, you know, explain how it can be applied to manage for these transformations.

[00:30:03] Nate Stephenson: Yeah, I will say I'm very fond of that framework because it's organized around classes of actions that managers can take. It's very management-centric and it's easiest to give some concrete examples. Like, for a resistance, you're thinking, Hey, I don't want things to change around me. And we were just talking about giant sequoias.

Maybe I need to irrigate some of my giant sequoias. It's getting warmer. We're getting more hotter droughts. You're trying to keep things the way they were. And under some circumstances, maybe you can maintain that in the long run, but a lot of the time you probably can't. Eventually, circumstances will overwhelm you and you'll lose what you were trying to preserve.

But one thing that resistance can do that's very important for managers is it can buy you some time. It can buy you time while you figure out what your next steps are and start implementing your next steps. So resistance is a viable and useful strategy.

Accept, the 'A' of RAD is, there’s, I picture someone who's just sitting back and watching change happen on the landscape. And there might be two reasons for you to do that. One is it's a conscious choice. I'm trying to hedge my bets because the future is uncertain. I'm going to purposely leave some areas alone. ‘Cause I really can't predict what's going to happen, and I'll monitor and see what happens in those areas. But I'm not going to intervene there even though I might be intervening in other locations.

That's one form of acceptance. I think in the Southwest, another form of acceptance is imposed upon us. It's, these landscapes are just so vast, we can't possibly intervene everywhere on the landscape. And instead, what we do is we very strategically think about, well, where are we going to intervene? We designate some specific locations we're intervening, and the rest of the landscape by default we accept the changes that are happening. Just, it's just too vast out there. We can't do it all. 

Finally, direct is when you certainly, you just, you recognize that change is inevitable, but the hope is that you can nudge that change in a direction that might be more favorable to you. So we've been talking about these severe wildfires that basically reset the clock on the landscape. They, they kill all plant life and even the seed source. And you're left with bare soil that might erode during the next rain storms and maybe some invasive species, they'll come in. You know, one part of direction might be well, let's avoid that reset if we possibly can. So you try to treat the landscape in a way that makes it more resistant to wildfire, changes from wildfires. Also direction could be in those places where the clock really has been reset. You suddenly have a barren landscape in front of you and you decide that you need to replant, intervene. Maybe you bring species in from lower elevation or from the south.

And so you're, you're reshaping the environment with regionally native species that are probably better adapted to the warmer climate that we're in now. And that as far as we can tell, we'll continue to be in going into the future. 

[00:33:47] Sarah LeRoy: Thank you for that explanation. And Craig, I'm wondering if you have anything to add and maybe if you want to talk about some pros and cons of this RAD approach. 

[00:33:57] Craig Allen: I will say that the assisted migration approach of actively moving species around is, there's a lot more discussion around it.

It used to be a topic that in terms of authenticity of ecosystems, particularly in places like a park service unit, that would be kind of a pretty extreme idea. It still makes me a bit uncomfortable, as well, in the national park setting. Because to some extent, these are places we try to be conservative with in terms of the management. You know, the park service legislated guidance is to maintain the parks, their landscapes, the resources, unimpaired. Unimpaired. And that's hard to know what that means in a global change world, not just climate change world, but a global change world where things like, when we're inadvertently translocating species all over the place. You know, Eastern US forests, one of the biggest issues is really invasive insect and disease pests.

Have just really been such a huge issue there. I have mixed feelings about it, but clearly, but the pace, the pace and scale of transformation associated with ongoing climate change right now is thought to probably, or at least potentially exceed the ability of, of tree species to track it. That it takes a long time.

And so it's something to think about. I know Nate, you'll know this, but Pete Fulé, a professor at NAU, just put out a call looking for a PhD student to work on a consideration of translocation of Chihuahua pine northward. It exists in, you know, Southern Arizona and the southwest corner of New Mexico.

But it's a pine species better adapted to higher severity fire disturbance. And of course the warming climate, ‘cause it has both serotinous cones and it can re-sprout to some extent. And so I mean, people are really thinking about it. One thing from a practical standpoint, that for a few years, I've been suggesting the land managers.

When, if we're thinking about translocating locally, take species that are - the north and south facing slopes in the whole Southwest region are like different environments. So that sun exposure, it's so much warmer and drier on the south aspect. So if you take species from the south side and you, if you're planting stuff, move some of them to the north side and you know, that's kinda like ah, assisted migration lite, I suppose, but it's a way that's less controversial that you could do that locally and practically.

That would buy some time. I think a lot of these measures as Nate says, are really about buying time. That for forests, you know, from a forest standpoint, we do, we hope to buy enough time, by some of these management measures for big old trees to have a chance to survive the 21st century. Fortunately one of the things, one of the treatment measures to reduce the density of the understories of these many young trees that have come in, in the fire suppression era of the last century plus, that not only reduces the fire hazard, it's not only historically moving these forests back to the conditions they were in for many centuries, but it's also one of the best ways to reduce the competition for water as well as flight and space with the big, big old trees on these sites.

So it gives them a better chance to survive the growing climate stress on these sites, irrespective of fire. 

[00:37:51] Sarah LeRoy: Thank you, Craig. It really is a different world that we're living in right now. Managers having to make these decisions about, you know, physically moving species and, or leaving things the way they are, waiting for change, buying time.

And so Nate, I wanted to talk about a publication that you're a co-author on. One of our guests actually referred to the publication in one of our previous episodes, when we were discussing adaptive silviculture. And we, in that episode, we discussed adaptation options, similar to RAD but that, what we were discussing in that episode was more focused on resistance, resilience, and response.

So are you seeing managers take these, you know, different adaptive management strategies? 

[00:38:36] Nate Stephenson: Yeah, I think there's a lot more similarity among these different approaches than might meet the eye initially. The RAD concept that is in favor right now is very similar to, a lot of real good work has gone on over the last 10 years from different groups all over.

Who have had converging ideas that ended up being really similar in the end, there might be slightly different emphases, different nuances in them, but I think any of them can be a great place to start. And you find the one that resonates with you, and I'm going to point everyone to the most recent issue of Bioscience. So it's the January, 2022 issue of Bioscience, has a special section on RAD and it's, it's wonderful. And I especially would direct people to the lead paper with lead author Gregor Schurmann. It, it has some wonderful sections on the history of the concepts. And then it has a very good literature cited section.

So you can read through that and, and see the different ways people have been thinking about how do you manage in the face of, you know, radical ecosystem transformation coming down toward you. So, yeah, I definitely would direct people to that. To my knowledge, that is the most recent authoritative analysis of these related concepts.

[00:40:03] Craig Allen: So Nate. How have these recent, severe wildfire episodes affected management thinking at Sequoia national park?

[00:40:16] Nate Stephenson: It's interesting that before the severe wildfires here, there was discussion going on about maybe doing an assisted migration experiment for giant sequoias. And in my mind that experiment would have been as much a social science experiment as it would be a biological experiment because you know, the public has an idea that, I mean, effectively they've been promised that national parks will be kept looking the way they look indefinitely, and that's becoming impossible. So what do you do when it becomes impossible? So to start adapting to the future, you have to engage the public. And the idea was maybe there needs to be this assisted migration experiment for giant sequoias, and you bring the press out, you bring interest groups out, you show them what you're doing, you talk it through and you see what happens.

So those discussions were starting and then we got hit by the wildfires. And it's fair. I think it's fair to say that those are still so recent and so severe that we're still getting our feet back underneath us after that. But the new thing we saw of cones being burned out of the, the tops of the sequoias during crown fires, meaning there's no regeneration in some of those areas of crown fire, has got the idea going that we need to actually replant sequoias in some of these areas where it's not happening naturally, like it used to in the past. And a possibility that goes with that, and it's only in the discussion phase there is nothing planned for yet, but it's in discussion, is - well at the same time, if you have a whole slope, that's been slicked off by the wildfire, why not also plant some sequoias at higher elevation right above that? Right above where that grove was. So, you know, those are early thoughts, but I think it's going to take a calm period and more focused, more thoughtful discussion. 

[00:42:37] Craig Allen: So Sequoia National Park is now on the slippery slope of the gardenification of nature that Dan Janzen wrote about 20 some years ago. That's gardenification. I think. I'm not sure if I'm remembering the title of the article right. But he wrote a provocative piece, as a perspective piece in Science, Dan Janzen, alright. The eminent tropical biologist, uh, worked on the restoration of dry forests in Northwest Costa Rica, right, Santa Rosa National Park, that whole area. 

I mean, basically, you know, from a biodiversity standpoint, we have to accept that we can't hold it static and human influence is so great, in the perspective he put out there. None of it is, it's all affected by humans now. So we have to take responsibility for it. At one degree or another.

And I'm just, this is the part that on the Park Service, this is kind of a culture shift. You're hearing a conversation here you know, what Nate just reported is that, you know, in the Park Service, moving the iconic flagship species for which that whole park was established and deliberately planting them in a spot they weren't before. Moving them, even albeit adjacent, adjoining and totally logical of course, but it's, that's the, I think the counter argument in part has been that it is a slippery slope once you step onto it. Because at that point, once you start making the decisions about where things, where different species should be, you know, our hand print, you can't deny our hand prints are forming that system anymore.

Anyway, it's part of larger philosophical conversation that is what does “natural” even mean in a world that, you know, humans have always been interactive with and are now such a force that arguably we're in the Anthropocene. No longer the Holocene, that we're a geologic force. So it, it may make perfectly good sense, but this has, it's been a very unsettling time. This last part of our career for Nate and I. For land managers. Very unsettling time. 

We've, you know, the last 20 years it's been building, but the verities of the past, this historical range of variability as kind of the template as a guide, not just in parks, but in other land management agencies. This is what worked naturally was kind of the, the guiding idea and “Stationarity is Dead”. That was the title of another prominent paper, right, that some of you know. And that's, that's true for vegetation now as well. That it's in transition to something different than what it was historically. 

These ecosystems are in the process of reorganizing and in some cases, dramatically and nearly overnight, you know, some of our management efforts are indeed just trying to foster the potential for those transitions to be more incremental. So to let nature sort it out without it being through a huge, hard reset filter, like very large patches of high severity wildfire. But yeah, these, these are all active questions and I mean, at one level it makes it an exciting time, and a consequential time, to be working on these issues, moving forward.

[00:45:55] Emile Elias: That's such a deep and broad topic that we're hosting a series on it, and we'll be lucky to actually have Christy Brigham at Sequoia National Park with us on a later episode to take a deeper dive into some of these really challenging questions. And your conversation already led to the last question that we had considered asking you, which is really, what kinds of things does a land manager have to consider when proposing these major scale changes or translocating species outside of a native range?

Like where, where are we going here? And Nate, I wonder if you have anything that you'd like to add to what Craig was just talking about. 

[00:46:41] Nate Stephenson: Yeah, a follow up on this idea that this legitimate fear of turning natural areas into gardens. I've given talks before that threw out the possibility of assisted migration and more intensive manipulation, and had some people in the audience get pretty angry with me.

And what it turned out was happening was we had different visions. They had the vision that the entire landscape, every square inch is managed. And for me, the vision was, boy, if we're lucky, we're going to intervene on 1% of the landscape. It's just too vast, but we need to strategically pick some small areas.

So maybe we will do something kind of like gardening, but at least in the landscapes I work in, it is going to be a tiny part of the landscape, most likely. Just because we don't have the ability to intervene on a larger scale. Carrying on with the idea of assisted migration - of course, one of the biggest things you need to watch out for is unintended consequences.

And I like the example of wolves being reintroduced to Yellowstone. Which is, you know, putting things back to the way they should've been all along, rather than bringing something entirely new in. But what that reintroduction of wolves showed us is how bad we are at predicting outcomes when we introduce something and we could go on and on about it.

But there was a whole sequence of cascading events where the reintroduction of wolves led to a big increase in beaver populations in Yellowstone. And it had to go through a whole bunch of steps to reach that point. And I don't think anyone predicted that ahead of time. And it's an outcome people are happy with, but it just, it illustrates the point that you can have pretty serious unintended consequences, introducing organisms into a place they haven't been for a while if ever. 

But what I will say also is if your assisted migration is to assist a species that would probably migrate on its own if it only had 50 more years, but it just doesn't because the change is happening too rapidly.

I think people are in a better position to accept that. It's close by. You can make the case that if this change were just happening a little more slowly, it could keep up with it. But it's happening so rapidly it can't. So, yeah, we might need to get in there and assist that migration. 

And engaging the public on that, again is, the promise the public got: the national parks would be kept the way they looked indefinitely going into the future, and that there would be minimal human interventions. And now you're seeing a need to intervene that really does take good public engagement and, and listening to the feedback, and making decisions, you know, hopefully coordinated with other groups that have a vested interest in the, the future of the landscapes you're working on. 

[00:49:46] Emile Elias: Thanks Nate. That was a great dialogue. Great conversation about a really important issue, especially around our perceptions of what, what is natural and what our natural landscapes look like.

And it makes me think of something that gives me hope, which is that it feels like there's a much more rapid, deeper understanding of climate change and of what's happening on the landscape within the public. And so we like to end our podcasts, our conversations on a hopeful note. And so we always ask at the end, what makes you hopeful for the future?

Especially when you're thinking, in this case, about ecosystems and potential transformations that may occur, what are the things that you hold on to in terms of hope? And we'll start with Craig.

[00:50:35] Craig Allen: One of the things I find hopeful is working with young people. There is so much energy and enthusiasm and, and recognition, increased recognition of the need and the opportunity to be engaged.

So, and there is. There's just this huge need and opportunity for societal learning that calls for partnerships among scientists and land managers in particular but society at large as well. And so, so I'm hopeful that there's, there's there's a lot of people who are working on these things in so much depth and in so many ways that it's, I mean, 40 years ago, there wasn't even a glimmering of a lot of these issues and now they're becoming central questions. And I think over the course of the next decade or two at most, we're going to, I think it's going to reshape how land management is both performed and taught. And what has been thought of as pretty wild landscapes in the west. 

Another thing that I find hopeful is I see more science management partnerships emerging, and they're very real, increasingly real. I think there's a recognition of how important they are. Nate and I come out of a tradition in the Park Service, where there was a bit of that. They had a few scientists in a few parks and by being co-located together that kind of magic happened, in many cases, of, of high quality long-term science management partnerships. But it sort of seems like I see them developing around involving all manner of state, local, private people, managing lands, wanting to be better informed and wanting to work with scientists and often involving students and young people.

So there's this, there's a lot of dynamism around this, probably because the need and the opportunities are so great. 

[00:52:24] Emile Elias: That's a great answer. Nate, the same question to you. What makes you hopeful for the future?

[00:52:29] Nate Stephenson: It was instant. My response is the same in that the younger generations make me hopeful about the future.

And a part of that is, I'll speak for myself. I carry baggage. And my baggage goes way back to the late 1970s where I embraced what was called the Leopold Report. It was an official policy document of the National Park Service on, on how management would go forward. And it had this idea of, yeah, you keep things within the bounds they were within in the past.

And, shedding that was painful and difficult and took years. And the young people I work with today aren't bogged down by that. They, they already accept a lot of things that it took me years to finally accept, and they accept that a change is inevitable. They accept that the Leopold vision needs to be replaced with a different vision.

So I do get a lot of hope from the younger generation and it doesn't even have to just be young people. I, I wonder if the public at large, as, it's unfortunate, but as more of these sort of disasters happen where you lose a whole bunch of forest and it's scorched earth left behind. That's capturing the public's attention in a greater and greater way. And the public engagement into solutions will become stronger through time. 

[00:53:59] Craig Allen: Do you worry at all Nate, about coming generations and the public at large? Becoming sort of unmoored entirely from what was and what is possible? I mean, I think of, again, ancient, iconic trees as they're, they're kind of anchoring points for that, right?

These trees, that's part of why they resonate. They live so much longer than us, old ones do, right? They're touchstones of continuity and in the world, I worry about a thing about the, sort of the idea that people who've only grown up in cities. They live in man, in human made environments, in the sense that we can just terraform everything that everything is, everything is so dynamic that it really doesn't matter what it changes to. That one could indeed “Accept”. Go to the 'A' in RAD, and like, don't worry, be happy and we'll live with whatever comes out.

Which of course, we will. There will be forests. There will be vegetation growing on these sites. There is winners as well as losers, but what do we lose with what is lost from historical forests? That's why I'm a bit of a relic too with baggage Nate, thank you, but it's consciously so. Because I, like you, value those historical forests.

I knew them as they were. Differently, even though they were in transition and you could see their vulnerability, but I value that. Anyway, I just wonder what you've thought about that. Cause I bet you have. 

[00:55:28] Nate Stephenson: You know, one way of rephrasing what you're talking about is shifting baseline. Which is, people who come to work in the Sierra Nevada now at a young age, here is someone who's 22 and fresh out of college. The baseline is we've already lost, you know, somewhere approaching 20% of all big sequoias that's, that's the new baseline that they're starting from. And so it's in a sense that's normal because that's what you're starting with. I think there is some risk in, I agree with what you're saying, that people who don't live year round in a landscape for decades, have less of a sense of the change going on in those landscapes. But a lot of communication is going on also. And in the end, I'm not sure how valuable that communication will be. I think it's valuable. Trying to get people to grasp the significance of these changes and what it will mean for the future.

You know, what will it mean for their children? Giant sequoias aren't going extinct. But we could lose an awful lot of the big ones, maybe even the majority of the big ones. And as you say, those are the ones that give people goosebumps. That affect people deeply and profoundly. So maybe, I'm, maybe there are certain iconic species or iconic landscapes that better engage the public or best engage the public because it resonates with people most strongly. That can be a lot of communication about the changes that are happening there and what those changes mean and what might we do about it to, as best we can, maintain those iconic landscapes or species.

[00:57:13] Emile Elias: What I heard you say, both of you, is that the landscapes have changed, the landscapes are changing.

They're changing faster than we thought they would. And people are changing too. And it'll be very interesting and dynamic as we go forward in responding to this. Nate Stephenson, Craig Allen, thank you so much for talking with us today. We really appreciate your experience, your time in the places where you've lived and worked for 40 years, and sharing your perspectives with us. And for our listeners, stay tuned. In upcoming episodes we will talk with some researchers and managers that are implementing projects aimed at managing for ecosystem transformation, using the RAD framework and assisted migration. Thanks for joining us.

Thanks for listening to Come Rain or Shine, podcast of the USDA Southwest Climate Hub

[00:58:10] Sarah LeRoy: and the USGS Southwest CASC. If you liked this podcast, don't forget to rate or review it and subscribe for more great episodes. A special thanks to our production crew, Skye Aney and Reanna Burnett. If you want more information, have any questions for the speakers or would like to offer feedback, please reach out to us via our websites.