AoR 152: Nathan Sayre on the Genesis and Limits of Carrying Capacity

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>> Welcome to the Art of Range, a podcast focused on rangelands and the people who manage them. I'm your host, Tip Hudson, range and livestock specialist with Washington State University Extension. The goal of this podcast is education and conservation through conversation. Find us online at artofrange.com. Welcome back to the Art of Range. My guest today is Dr. Nathan Sayre, a geographer at UC Berkeley. And the last time we talked on the podcast, it was about Nathan's book, Politics of Scale: A History of Rangeland Science. And that was Episode 12 and this one will be probably Episode 152. So if you, dear listener, are a recent convert to the Art of Range it'd be worth your time to listen to that interview and get the book. I don't get any royalties. The book ought to be required reading for anyone working in or studying rangelands. I came back around to this because I was recently talking with a really good scientist about a grazing decision support tool that we've recently built called StockSmart. And I was attempting to explain how I conceive of the relationship between grazing planning using stocking rate values and this concept of carrying capacity that remains in the rangelands world. And I suspect that if I continued right now using that term, carrying capacity, as if it were an established term of science, something concrete like the definition of a monocot or relative humidity, not many people would bat an eye. Some would but even those who could articulate the problems with the concept likely don't know where the term came from. I'm almost done introducing, I promise. So a few years ago, Dr. Sayre sent me an article that he published in the Annals of the American Association of Geographers in 2008 titled The Genesis, History, and Limits of Carrying Capacity. I'm not a regular reader of the Annals and I probably would never have run across this article if he had not sent it to me. But the article opens up like this. I'm quoting. "The concept of carrying capacity is employed in a remarkably wide range of disciplines and debates and it has been forcefully critiqued within numerous fields. Yet its historical origins remain obscure." I hope today to rescue the term's origins from obscurity even if that only serves to reawaken this critique. So Nathan Sayre, welcome back to the Art of Range.

>> Thank you, Tip. It's great to be here.

>> Maybe we should start with a definition. I am a card-carrying member of the Society for Range Management and the SRM's glossary that was updated in 1998 defines carrying capacity as the average number of livestock and/or wildlife that may be sustained on a management unit compatible with management objectives for the unit. And this is certainly, I would venture to guess, the way most range folk understand the concept. Is that the most commonly understood definition of carrying capacity, at least in the rangeland ecology world? And maybe I haven't asserted it but I would say that this has been a pillar of grazing management thinking, that at least once upon a time, you know, determining the carrying capacity accurately and then all of the, whatever decisions are downstream from that, that was like the holy grail of range management. Is that an accurate characterization and is the definition getting close?

>> Yeah, I think the definition is on the mark. It varies depending on the field and discipline, and it's changed a little bit over time in its wording, but the basic idea has remained the same for a very long time. I would hope by now that there would be a broader or perhaps different basis for or sort of holy grail for livestock and range management than that exactly. But I would agree, it does still play an important role and I think it is still the case that many, many people consider the concept pretty unproblematic. They might quibble about the details of the definition but they are unlikely to say this is not the kind of concept that we should use, that it's not going to help us make better decisions.

>> Yeah, later on in the paper, you discuss some problems with the concept in general but I feel like if I'm recalling correctly in the paper and at least in my mind, one of the initial problems has to do with the specific ecological conditions in the Western United States. And I think it ties into the very beginning of that definition. The beginning of the definition was the average number of livestock and wildlife that may be sustained. And as you've pointed out other places as well as other people, averages are elusive things.

>> Yeah.

>> There's a farmer where I live who's now dead, Ben George, who said to me one time, "I've been farming here for 70 years and I'm still waiting for an average one."

>> Yeah.

>> And you get at this in this other paper that I didn't have the time to read but the other paper on climax and original capacity I think was in ecological restoration. But you opened that book with an epigram from John Van Dyke from this 1901 work, The Desert. The quote is, "The most dangerous and difficult thing to set up about anything in this desert world is the general law or common rule. The exception, the thing that is perhaps uncommon, comes up at every turn to your undoing." I love that line. He doesn't just say that the exception is the rule in arid lands. He says that these anomalies, but I suppose I can't say that because it implies deviation from some norm. These interacting variabilities maybe confound management if it's trying to move toward predictable results. But this idea that it's predictable and similar from year to year seems to not work. Is that --

>> Yeah. I think that's exactly right. That term average is it's -- how should I put it? It's a little bit sneaky. The way -- it seems perfectly innocuous. We all know what an average is. It seems like the obvious way to think about a decision like stocking a pasture. And yet, as many, many ranchers know very well, and your former farmer neighbor as well, average doesn't tell you what's going on right now. And what's going on right now is likely to vary significantly from the average. And indeed, those are the conditions to which you need to respond and make your management decisions. Interestingly, and the thing that got me interested in the topic is the fact that I was doing work on the origins of range science. I was looking at the earliest scientific work trying to evaluate rangelands and livestock grazing. And these were reports written by a government agency in the 1890s. And they used carrying capacity without even pausing to define it or explain how they had arrived at the idea. And it was clearly just an idea that was in their heads and they used it. And that got me to wondering, well, who did ever define this or explain it or come up with it in the first instance? And those same western rangelands have indeed been a place, as in many other disciplines, where the term gets embraced and applied and used, and in many cases elevated to some importance in the science and sometimes management of natural resources. And it takes several decades before experts in that specific field come to the conclusion that the concept doesn't work for them, doesn't work for the systems they're trying to understand. And it is about the complexity of interacting variables, the unpredictability of key drivers, the conflation of different factors in trying to understand change and make decisions on the basis of this idea. And so then I was pushed to ask, well, how did the idea come into being and what were the conditions and assumptions or premises built into the idea when it was first conjured into being?

>> I think you mentioned in the introduction that the term, carrying capacity, had been used in wildlife management, chemistry, medicine, economics, anthropology, engineering, population, biology. Which of those came first or none of them? At what point, what was the 1890s publication that you mentioned? Was that the first mention of the term or the concept with respect to range management, and what was before that?

>> It was almost the first in range management, but it was definitely not the first in other fields. Its origins actually lie in the 1840s, perhaps slightly earlier in the context of, believe it or not, international shipping and specifically questions of tariffs and how were tariffs levied on ships carrying cargo. And the key thing to understand is that there had been a system in place for international trade that established what they called a tonnage for a given boat. That number was defined from the outside, you might say, looking at the external dimensions of that boat and calculating in volume terms roughly what it could hold. And tariffs were applied to that boat for that amount of cargo in and out of ports all over the world, no matter what the actual cargo happened to be on a particular trip.

>> Right. Because the displacement of the ship would be equal to the weight of the water that was displaced by it and so you could have a 150-ton ship.

>> I believe actually it initially was about volume rather than weight, so it wouldn't have been displacement unless you could compare the boat empty to the boat. And even if then it became -- there were two terms, tonnage and -- now I'm drawing a blank. Tonnage was the volumetric. It was based on a word ton that referred to a cask and a lot of cargo was packed in basically barrels or casks for transit. I'll come up with the other one. The other one was about weight. But tonnage became the term that was in common use and it worked well enough. In other words, it was a lot easier than actually trying to measure the volume of the cargo every time you came and went and take all that cargo out of your hold and measure it. That would be a very inefficient way to go about. Everyone had an incentive to pack their ship as full as they could and the numbers arrived at by measuring the hull and then doing some math were suitable. The problem arose when steam technology came along and suddenly you had a very different kind of boat that was engaging in international trade and tariffs were being applied. And steam ships, as you can imagine, they don't just have a big, empty, hollow hull that you can fill with your cargo. They also have big machinery and they have coal, and they have water that they have to feed into the steam engine in order to make the boat move. All of those things take a great deal of space. They're very volume, you know, demanding of volume. And so the owners of these steam ships objected to being levied tariffs on the basis of tonnage. Their boats, they said, actually had less room for real cargo than the hull would suggest and therefore we need a different way of measuring what they came to call the carrying capacity of the ship. And that's what we should be taxed on, effectively.

>> You point out several times in the paper that one of the main impulses, to define this was for the purpose of taxation. What are other ways that that has been applied?

>> Over the years, it's been applied to all different kinds of things. Carrying capacity, for example, is used to evaluate how many skiers you could have in a ski resort. It's been applied to think about the number of, the amount of water that can flow through either a canal or aqueduct or also actually, natural features, estuaries and bayous, things like that. It's been used to measure how many deer you should allow hunters to kill in a given area in a given season. The list goes on. And in fact, I mean, the closest to the original use of carrying capacity that we're accustomed to using regularly now is payload. You talk about the difference between a half-ton and a three-quarter ton pickup truck. Those numbers are referring to the payload that that truck is assigned by its builder, engineer. And that number is obviously an approximation. If you have a half-ton pickup truck and for whatever reason, on a given day, you happen to put more than half a ton of cargo in it the truck will probably be fine. It's not a strict limit. It's a design feature.

>> The amount of x that y was designed to carry, not what it could actually carry if it was pushed.

>> Yes. And the thing I noticed in looking at this history is that it begins in these contexts where it is engineering. It's a designed system that you can carefully control the tolerances and the strength of the materials and things like that. And you can actually design to a carrying capacity that you wish to achieve. Over time, over decades, the concept and the term gravitated to situations that were increasingly unlike that. Situations where it was not about engineering, it was about a natural system where the sort of ideal, the notion that it was fixed, that it was a static quality of something simply was inappropriate, as with a pasture or a unit of rangeland. And yet it held on. It retained this ideal quantitative sort of static quality, even though in the context to which it was being applied it was not a reasonable assumption to make.

>> Yeah. Regarding some of the examples, a mule does have a limit to how much meat it could carry on its back --

>> Yeah

>> -- walking out of the mountains. But you take an ecosystem of whatever scale and then apply that in the abstract or the figurative sense and you have a problem of scale, to borrow the title of your book.

>> Yeah. Yeah.

>> That's not the only problem. That's one of them.

>> Yeah. And the things to which the idea was applied also gravitated first from engineered systems to sort of natural systems. The question of how much floodwater could a bayou contain, for example. And then eventually it migrated to livestock and beasts of burden. How much could a team of mules carry, for example? And then it made this key shift from how much x could a y carry, like how much weight could a mule carry, to how many mules could a pasture support? Or eventually, how many humans can the planet support? It gets flipped around and now it's a much more sort of figurative sense of carry and it is asking about relationships between populations and environments. And carrying capacity becomes a kind of interesting way of thinking about something like overpopulation.

>> Yeah, I love the quote from this -- the idea seemed to hit the ground running in the livestock world. You have a quote from I think the Journal of Science in 1889 regarding Australia, using this as a measure of range productivity. The quote from the journal was, "Australian records show that land favored with less than 10 inches of rain a year is quite valueless without irrigation. In such regions, only one sheep per square mile can be carried for each inch of rainfall. For from 9 to 13 inches, however, the increase is about 20 sheep per square mile. And from 13 to 20 inches of rainfall, the increased carrying capacity is about 70 sheep per square mile." I've heard similar rules of thumb quite recently which -- I grew up in Northern Arkansas and on some of those grasslands where there's, you know, 50 inches of precipitation per year, even if you have some 10 inches of deviation from that, you have pretty consistent forage.

>> Yeah.

>> Where you could make some rules of thumb and it's going to be on 9 years out of 10.

>> Yeah.

>> Because it's not the southwest desert. But in these places, it probably does not work so well. But even in Australia, you know, this was also intended to provide a basis for lease fees and taxes based on livestock. Is that right?

>> Yeah, absolutely. You know, the British were trying to settle colonists across Australia. A lot of the land couldn't be used for growing crops and settling farmers. And the use of that land for livestock production quickly emerged as the most promising route for creating the kind of settlements and citizens and economy that the British hoped for in their colonies. And yet, from that vantage point, you really want to allocate land in such a fashion that you are ensuring that each family has enough land to make a living, and also not giving them more than that because that would mean fewer settlements -- or settlers, less land for other settlers. And this same exact predicament was confronted in the United States when the federal government, beginning with the Forest Service, was trying to decide how to allocate access to public grazing lands. They wanted to give enough land but not too much, which meant they needed a number. They needed a way to say this much land is required to support this many animals. And that needed to be a stable, fixed number because you were talking about writing leases, assessing taxes and ultimately building fences that would make those areas fixed. The temptation was, I would say, bureaucratic, administrative, to some degree political. And as that passage you quoted indicates, the problem is that some years it rains and some years it doesn't. And the difference between 5 inches of rain and 15 inches of rain in terms of the amount of forage that will grow and the number of livestock that it can support is huge. And that is going to make these averages, these fixed carrying capacities truly a problem.

>> Yeah, that makes me think of this. There's another word that is really common and still exists in public land lease language, range improvements. And in this portion of the article talking about taxation and sort of fixing these carrying capacities in Australia and New Zealand, one of the effects was to increase investment in land improvements. Was the idea there that the land improvements would increase the carrying capacity above what would have been called original capacity? Or was the idea that it was mostly just allowing someone to realize, I guess in an economic sense, the fixed original capacity?

>> This is the heart of the problem in the concept of carrying capacity as it's been applied in different non-engineering settings. And that is, it suggests the existence of a stable number, a quality or an attribute that is not going to change. Once you have sort of given yourself the freedom or the permission to think that way about something like a pasture or a grazing allotment, you are committed to the existence of an ideal basically or an average, either way. And actual reality at any moment in actual time is going to deviate from that norm or that average or that ideal. So then you have to come up with some way of thinking about the relationship between the actual carrying capacity at a given moment and this ideal carrying capacity that sort of goes, is built into the category, the concept itself. And so different ways of thinking about this, original capacity was a name that was -- that was what precedes your sort of arrival on the scene. It's nature's carrying capacity. It's considered to be the true, at least potential carrying capacity. On the other hand, you have an actual carrying capacity. Improvements, yes, were intended to raise the carrying capacity, perhaps raise the actual carrying capacity by remedying some deficit that had diminished the actual carrying capacity from the original, perhaps by allowing the system itself to sort of heal. If you find a grazing allotment that appears to have degraded or doesn't have as much grass or as many of, you know, the grasses that you would like to see, perhaps reducing the stocking rate will allow that pasture to recover, simply because you're not putting as much pressure on it from livestock. In either case, there is this tension between the ideal and the actual. And there has been a kind of schizophrenic approach to this in many contexts in which the ambition to change the carrying capacity is kind of forced into the same frame with the conviction that carrying capacity, in some sense, is fixed and static. The Forest Service sort of embraced this very much in its early grazing sort of administrative rules. And they would tell a rancher, "Yes, this allotment has an assigned carrying capacity of, let's just say, you know, 500 AUMs. But however, right now, we need you to run 300 AUMs so that it will come back to its full capacity down the road." And a rancher, you know, 300 AUMs might not pencil out. Moreover, there were probably years when there was plenty of grass for 500 AUMs. Why can't you graze it? Well, the Forest Service would say that doesn't conform with our understanding of how we can take best care of this allotment.

>> Yeah, and even there, we're talking about percentages like plus or minus 50%. But in this, you know, speaking of ambition, in the quote about these range improvements in New Zealand, it said. "The stock carrying capacity of the land and the wealth of the country was therefore by this process made seven or eight times what it was before."

>> Yeah.

>> Much to the relief of English bondholders, you know, you go on to say, that is crazy.

>> Yeah. You know, if you read the famous report that the Secretary of Agriculture put together, actually the Forest Service put together for the Secretary and conveyed to Congress in 1934, the one that's called the Western Range, very similar assertions were made by the Forest Service at this critical moment when Congress was debating what to do with the remaining public domain. And the Forest Service was convinced that they should get control of the remaining public domain, the land that we now know as BLM land, because of their track record managing the national forests. And they came up with all kinds of data to support the contention that the rangelands under their care had improved in carrying capacity in the time since the Forest Service had been managing them, whereas the public domain and even private lands, it said, had continued to degrade. And the gap there, you know, was asserted to be quite significant. Obviously, BLM land on balance tends to be drier than national forest land. There are all kinds of ways in which this comparison was, even at the time, fraught with problems. But that's the kind of logic that this concept tends to induce in people.

>> You mentioned in the article that Fred Clements rejected the idea of fixed carrying capacities, but he's also the one who's credited with the climax theory. And those two things would seem to somewhat go together. What was his thinking on this?

>> I think he would have said these are very different questions, that the climax is useful for thinking about vegetation dynamics at large. And that when you're talking about carrying capacity, you really are asking about decisions that are in real time, you might say. They are not ideal. He recognized great inter-annual variability in the Great Plains and in the effects of bison grazing, for example. He saw that in drier years, drought periods, bison populations would drop perhaps significantly. He saw that when a bison herd went through an area, when it left, it left in part because it had literally consumed all the vegetation and it needed to move to find fresh pasture. Those types of variations he understood to be sort of built in to the dynamics of that grassland system. And that was what he would say was relevant to calculating the number of animals you would put on a pasture in a given year. And the fact that he was quite explicit about using bison as an analog for livestock or for cattle. And he was quite aware of the great variability in bison populations and their movements. And yet those aspects of western rangelands, the variability, the need to move or the need to respond to unpredictable variation, did not catch on the way his idea of climax caught on. And you're right. I think there is a tension there. I think it points to the fact that his theory of succession and climax was embraced by the Forest Service for grazing management and administration well before there was a solid empirical scientific basis to support it. And for reasons that were really not about whether the scientific community had agreed on this concept or this theory. It was about the needs of the Forest Service and its bureaucratic sort of logics vis-à-vis, ranchers and their interests in grazing animals on those lands.

>> Which included the bankers.

>> Yeah. I mean, any rancher is going to need to be able to somehow capitalize, collateralize a grazing permit. And the bank wants to know, well, how many animals can you raise on this allotment? And the Forest Service needs to be able to answer that question.

>> So the plant succession referred to species composition or plant assemblages with some variation. But carrying capacity referred to poundage, literally, like with ships. And it needed to be stable for government purposes and financial purposes.

>> Yeah. Yeah.

>> At what point did the idea of carrying capacity enter into wildlife biology? Did that follow from the way it was used in livestock grazing? Because it doesn't seem like there's much talk about it prior to Aldo Leopold.

>> Yeah. No, in this case, we actually can specify with great detail when and how it transitioned from one range of application to another. Aldo Leopold, of course, worked for the Forest Service right after college. He'd been working with the Forest Service for about a decade when he was assigned for I think less than a year to the Office of Grazing in the regional headquarters in Albuquerque. And in that setting, he came across carrying capacity as an idea that the grazing administrators used in managing allotments and permittees. And he subsequently put it to work in thinking about wildlife populations and particularly game populations like deer and bobwhite quail needing, again for a public agency managing a public resource and trying to satisfy the demands of a constituency or several constituencies, in this case hunters and anglers as well. Carrying capacity became a way of thinking about how many deer could be safely harvested, how many deer would survive in a given area. And the ideal was still there, you know, the notion that these areas needed to be managed to get back to or achieve the ideal populations of deer or other target species. And to his credit, he recognized the variability in the populations that could be supported on a given piece of land. And he wrestled with that and distinguished between carry capacity which he said was an attribute of the land itself and was subject to change based on conditions on that piece of land, including the impacts of wildlife themselves, versus what he called saturation point which was the population density that an organism, whatever that organism might be, bobwhite quail, for example, could achieve in ideal conditions that was a feature actually of the organism rather than the habitat. And he wasn't convinced that saturation points actually were stable for many species. He recognized that we had very little data to go by and that in any actual population, of course, there's both the organism and the environment. And figuring out how much of the population, the sort of determination of the population as a function of the environment and how much might be intrinsic to the organism is a very difficult thing to do and perhaps impossible. But he nonetheless counseled that if you're a sort of smart, observant game manager, what you're managing is the habitat and you're looking to figure out what's the limiting factor. Is it that there's not enough food for this game species? Is it that there's not enough cover or vegetation of a certain structure? And you try to tweak those elements one by one, fix them or make them better. And as soon as you've fixed one, you'll want to figure out what the next one is because you're, you know, incrementally bringing conditions back to what will support the carrying capacity of that species in that range.

>> I can't resist comparing that to what William Denevan has written about in the handful of articles he's written on The Pristine Myth. It feels like even the observations, both anecdotal observations as well as, you know, whatever empirical measurements have been made with wildlife populations in the early part of the 1900s, all of that feels like it's maybe still a couple steps removed from the original source of the conditions they were seeing. And of course, as you're likely aware, you know, his contention is that probably all of those things, both vegetation and wildlife, had been held in some kind of a check by a population of Indigenous peoples that was likely much larger than we have historically thought or accounted for. So you had both the near extermination of Indigenous peoples and whatever effects that had on plant communities and wildlife. And then you also had Europeans that nearly exterminated all of the predators that also would be providing some kind of a check on the populations. And I think we talked about that some in the interview about your book. But to make the assumption that the deer populations are only a function of the plant community conditions observable at the time of observation might be short-sighted.

>> The controversy, the topic that Leopold found himself dealing with very shortly after he became familiar with the concept of carrying capacity was the deer population on the Kaibab Plateau in the Grand Canyon, where the government had set aside this area as a game reserve specifically to protect and enhance conditions for deer and very much supported by hunters who wanted deer populations. They noticed that deer populations tended to be dropping in a lot of places for precisely the reason you just pointed to. So what did the government do? They told people they weren't allowed to hunt there. They closed it off. And then they proceeded to eradicate all the predators, particularly wolves which is a topic of another famous Aldo Leopold essay, right? Well, lo and behold, what happens? The deer population rebounds and then keeps growing because there are no predators there anymore. And then suddenly the population collapses. This becomes something of an embarrassment for the government agency that's in charge. They kind of avoid the issue for a while. They try not to admit that maybe this problem, this collapse of the deer population is their own fault. And Leopold is one of the first to say, you know, those predators have got a role to play in keeping the population of deer from erupting, was the word he would use. And if you didn't keep them or if you didn't let the predators do that or hunt them to a comparable degree, what you were going to get was a collapse by virtue of overgrazing or overbrowsing. The habitat would be destroyed precisely by the abundance of deer.

>> Yeah, you quote him from 1936 in the paper on that point. He says, "The obvious lesson is to not let a good herd irrupt," I-R-R-U-P-T. "To prevent an eruption, the herd must be kept trimmed down to a safe margin and the carrying capacity of the range built up so there's a safe margin of capacity above population." That almost feels like it's an oxymoron, you know, where the statement denies the idea of a carrying capacity but uses the carrying capacity to make the argument.

>> Yeah, Leopold, to his credit, was actually, I think he was more aware of this tension between an ideal number, an ideal carrying capacity and the actual conditions at any given moment or place. Many other people have conflated those two things and failed to see the ways in which it could create problems. But you're right, the passage does point to this notion that there's an intrinsic carrying capacity of a range for a given species and then there are things you can do to improve that habitat which from a practical point of view, makes a lot of sense. I think that's how we all -- like you can improve habitat by manipulating things in various ways and there's also probably a point at which you can't improve it any further. But that tension between ideal and real carrying capacities also has the potential to create significant problems.

>> Yes, we could talk about this all day but I'm interested in maybe shifting toward some of the effects on people.

>> Yeah.

>> You mentioned toward the very beginning of the paper that carrying capacity has almost always been deployed by institutions of the state. And it has often resulted in grievous errors of policy, administration, resource management, and ethics. Where are some other places where this has been -- we can see some of the obvious implications just from that quote from Aldo Leopold. We've got to prevent the population from erupting or exceeding this threshold or, you know, whatever the top of this sigmoid curve is in the, you know, stable population. Now we're talking about something that I don't know as much about and I'm interested in learning more about it. I actually talked with Maria Gimenez about this at the SRM a few weeks ago. And we agreed to visit about it some more on the podcast. Maybe we can loop you in on that. But this would be a good introduction to some of those conversations about how this concept has affected humans and how humans have treated other humans.

>> Yeah, the most egregious example that I've been able to find was carried out by the British colonial administrators in what's now Zambia in the early 1940s. A man named William Allen, working for the Colonial Department of Agriculture, was tasked with assessing the population of native Africans in the colony. The population had been disrupted already in many ways by the arrival of colonist farmers who were given basically the best land for farming and also mining, the big copper mines in the area that attracted a lot of laborers from the African population, sometimes from, you know, some distance away. And Allen was concerned that the population was maldistributed and that the result would be too many mouths to feed in some areas where the amount of food that the native population could produce would not be sufficient, and that on the other hand there were also areas that were, so to speak, underpopulated. He relied on a map that had been created by some scientists in their administration to map the productivity or productive potential of land in different parts of Zambia. And then calculate from there the amount of food that could be produced and therefore the number of people that could be supported. He crunched all these numbers and arrived at the conclusion that 160,000 native Africans needed to be moved in order to abide by the carrying capacities of the land, 50,000 or so were in fact relocated. The report tries to make this sound like they simply persuaded these people to move but it's quite clear that in fact, the colonial administrators simply said, "You've got to go." And they said, "If you go, we'll give you a certain amount of land in this other area. If you don't go, we're just going to force you to go." Here was a case in which carrying capacity authorized this kind of coercion on the grounds that it was a scientific assessment. That it was, again, a number that could be not only identified but in fact was fixed. And they also allowed for the fact that native Africans farmed in different ways and that if they farmed differently, they might be able to produce more food. But of course, what they had in mind was farm, more like British farmers and so there was an element of coercion on that level as well.

>> I think you say somewhere in the paper, I'm paraphrasing here, but the ecologists suffered from physics envy. In our reductionistic thinking, we want to narrow everything down to what can be calculated and this shows up in these efforts to establish a carrying capacity for the Earth. And if there was ever a problem of scale, it seems like it might be one of them.

>> Yeah.

>> But these ideas maybe started before, I can't remember what the dates were for the stuff that Thomas Malthus was writing but you also quote William Vogt quite a bit.

>> Yeah.

>> And I had recently read about him in Charles Mann's book, The Wizard and the Prophet, contrasting William Vogt and Norman Borlaug, Norman Borlaug being the only plant breeder that ever got the Nobel Prize and is largely credited with, you know, establishing the modern science of plant breeding. And then William Vogt, interestingly, at the same time I was reading the book, The Alchemy of Air, about the invention of this process, the Haber-Bosch process to generate nitrate from atmospheric nitrogen.

>> Yeah.

>> And he comes up in there as well because he, for a while, was stationed on these mountains of bird guano off of the coast of Peru that were being harvested for fertilizer. And I think if I'm recalling correctly from Mann's book, one of the impetuses for the Germans developing this engineering process to create nitrate was that at the time, the British controlled the seas. And if the British decided that they weren't going to deliver fertilizer to German farmers, the Germans would be out of luck. But the story of, you know, William Vogt observing these just massive harvests of natural resources and then seeing, you know, sort of whole populations, you know, at a macro scale, the global level get disrupted by all of these things, fishing and birds. And it really influenced him to feel like there are some things that if we tamper with them too much, we might have a real problem which was likely true. But he defined carrying capacity using this bioequation, you know, C equals B, in relationship to E.

>> Yeah.

>> And tried to reduce it down to something that would be calculated.

>> Yeah. The idea of overpopulation, of there being too many humans for the world's ecosystems or the food supply, very much influenced by William Vogt and he was one of the important neo-Malthusians who revived a Malthusian perspective on these issues. And one of the interesting things I found in this research is that Malthus never used the idea of carrying capacity. The term didn't exist at the time. There was a gentleman by the name of William Godwin who criticized Malthus. Malthus published his essay in 1798. Godwin published a critique in 1820 in which he imagined that the world could support nine billion people. And he arrived at that number with some calculations based on arable land and the population density of China. But he was using it to make fun of Malthus because, of course, the population of the world at that time was nowhere near nine billion.

>> Right, a few hundred million.

>> Yeah. So, it's actually not until the 1930s, 1940s that scientists such as Eugene Odom begin to revive a Malthusian take in which you attempt to calculate how many people the world can support, using some of the same ideas that had been pioneered by people like Leopold and range managers. So, the term carrying capacity is applied to the world's human population only beginning in the 1930s, 1940s. It's a context in which there's eugenics. Ideas of eugenics are quite widespread. The notion that some people are superior to others or that the way people breed is an issue of public policy concern. Vogt, as you mentioned, gets stationed in the developing world during World War II and observes pretty dire poverty in rural parts of Latin America. And comes back from the war concerned that the carrying capacity of most of the planet is being exceeded or has already been exceeded and that the result is poverty, hunger. And that these are the bioequation, as you mentioned, of carrying capacity is the relationship between the biotic potential, which is the number of organisms that a species can produce if it has access to the resources it needs. And the environmental resistance, which is a way of referring to deficiencies in the habitat, you might say degradation. This equation, he says, you know, will give you a carrying capacity, the number of people that a place can support and allow you to conclude that much of the world is overpopulated. Of course, there's a conceptual circularity here in which because you start by assuming the existence of some ideal carrying capacity that is static and measurable, you then go out and look and discover that there isn't a place where this carrying capacity is, in fact, true and realized in real life. And that delta, that difference between the biotic potential and the actual population must therefore indicate what he called environmental resistance. Some kind of deficiency or indication that the habitat is damaged, degraded, reduced by erosion or poor farming practices or overharvesting of trees, deforestation, whatever it might be. This becomes the declaration of emergency. William Allen did something very similar in what's now Zambia. He was concerned that if they didn't relocate the population, there would be land degradation, as he called it, due to excessive populations in some parts of the colony.

>> The number, who was it that you said that came up with the number of nine billion?

>> That was William Godwin.

>> Godwin. That's really intriguing because I just ran a quick search. I think the world population right now is like 8.25 billion.

>> Yeah.

>> There's been a lot written in the last 10 years about the very high likelihood that it will cap sometime in the next 50 years at about nine billion and go down.

>> Yeah.

>> Because there are -- but the effective limits are proving to be sociological, not ecological or agricultural.

>> Yeah. Yeah. Eugene Odom, the famous ecologist who brought carrying capacity to bear on the discipline of population biology back in the middle part of the 20th century, he recognized that his ideas could be applied to global human population. He said the population at that time was something like 2.3 billion people. And he said, you know what, the population growth rate is actually slowing down already and it will peak at 2.6 billion. Then he said, unless the carrying capacity changes, unless conditions for supporting humans change. And what did Norman Borlaug do? He helped create the technologies and seeds, the agricultural potential to grow a lot more food. That is a great example of what Odom probably had in mind. And indeed, the population has grown enormously since World War II. And that growth rate is now slowing down and the demographers can forecast that it will peak somewhere in the 9 to 10 billion range, somewhere in mid-century. That carrying capacity, if it is a carrying capacity, has obviously changed over time and it might change again. We'll see.

>> Yeah.

>> I shouldn't leave the impression that I think the numbers will keep going up. I'm actually comfortable with the projection that the demographers are offering. I don't think it's going to suddenly go up again but that's for reasons, as you say, unrelated to the environment or land degradation.

>> Yeah, I think it brings up another interesting point. I've been asked a few times, you know, why is philosophy of any use? My answer has been that science can help us understand what is but it doesn't do much to tell us what ought to be. And the thing that brought to mind a few years ago was an article by Thad Box in rangelands. I don't even know. I'm embarrassed to say I don't know whether Dr. Box is still alive or not but he -- you know, that generation, particularly in the world of ecology and wildlife, was kind of reared on Paul Ehrlich's ideas, you know, from the population bomb and the idea that we're going to overpopulate the Earth and we need to prevent the human population from erupting. And in this article, he was arguing, you know, his own philosophy in support of what he called an ecological ethic, where we would make decisions about human populations based on what's best for the Earth, you know, which is what we've been talking about. But in the article, he was fairly openly advocating for selective euthanasia in order to control local populations and gave an example from, you know, a supposed Indigenous people in Japan, I believe, where they would -- if the locals thought that they had too many people, they would stuff their babies in the snow to kill them when they were born. And they would take old people, once they could no longer be so-called contributing members of society up on the top of the mountain and leave them to die of exposure. And he was absolutely riding in support of that. It highlighted for me the importance of doing some bigger picture thinking than just what appears to be demanded by science. And of course, he felt like a scientific understanding of population dynamics required that of us in that it was necessary, you know, for the greater good to kill some.

>> Yeah.

>> Yeah, it's an interesting thing.

>> Yeah, I mean, and as I quote Aldo Leopold in a lecture he delivered to students at University of Wisconsin in the sort of lead up to World War II when he proposes that war is a mechanism by which the human species limits its population and that perhaps we could prevent war by controlling the numbers of people that live in the world. I think one of the take-homes for me from this paper and other research I've done is simply it matters a lot the kinds of ideas you use to think about a problem. And concepts like carrying capacity, they can be very helpful in certain settings and they can be unhelpful in other settings. If you study demography and population growth rates in the world in the last 100 years, say, there have been many attempts made to coercively prevent the population from getting bigger. The Chinese, of course, had their one-child policy for many decades. India in the 1960s, 1970s set up programs that more or less coercively sterilized people out of fear that the population growth rate was out of control. The funny thing is that these coercive techniques have rarely actually succeeded in bringing a population growth rate down. And the variables that do work reliably, regularly, and lots of empirical support don't have anything to do with fertility or, you know, sort of the direct activities of having more children. They have to do with the conditions in which people more broadly are living, especially things like health, access to education, stability of income.

>> Right.

>> When women have more access to education and jobs and sort of autonomy or -- they will almost without exception or at least taken as a whole, taken as a group, they will choose to have fewer children and the population growth rate will come down. These are measures that are a long way away from carrying capacity, you might say. Like where do you start thinking about a problem? How do you diagnose a problem? And carrying capacity has got some utility but its utility is really in those, that narrow band of issues where you have a pretty significant degree of control over the totality of the situation, right? If it's how many x can a y carry, how much control have you got over y? Is it a ship that you can build so that it definitely has a certain capacity? OK. In that sense, in that setting, carrying capacity makes sense and is useful. If it's something else like the world, you don't have that measure of that degree of control. And thinking that you, thinking with carrying capacity is implicitly to think that you have control that you don't have. Forest Service doesn't control the rain and therefore doesn't control the amount of forage on a grazing allotment. In that context, you're better off not using this concept to think about the problem. Just as if you're trying to control or affect the world's human population, don't start by deciding that some people are excessive and need to be gotten rid of. Or that there's some ideal number that you can achieve by controlling people's decisions about whether to have children. Think about the conditions that these people live in and the decisions that they make as a result of those conditions. Change those conditions and you can change their decisions about reproducing.

>> That's a great conclusion. In fact, you conclude the paper by saying, one can liken the world to a ship, but that does not make the world like a ship. And analogies are like that. They're helpful for understanding but usually understanding one particular thing and not the whole enchilada. And so your last words in the paper are, what is clear is that carrying capacity is a very dull tool for understanding the complex interrelations of humans with the face of the Earth. That's a good word. And this is a great paper and I hope we can get a lot of people to read it. Nathan, thank you so much again for joining me. These are important things for us to think about and to continue chewing on.

>> Thank you, Tip. It's always a pleasure to talk to you and I enjoyed our conversation. Thank you.

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