Author of Finding Lights in a Dark Age, Saying NO to a Farm-Free Future and A Small Farm Future
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Posted on May 14, 2012 | 7 Comments
A couple of posts ago I mentioned the issue of tillage in the context of the permaculture movement. Here I want to discuss another issue at the core of permaculture that troubles me, namely its emphasis on perennial plants.
A key permaculture theme is to observe the natural world and then apply its lessons in conscious human design. Looking at natural plant communities globally it’s striking that almost always they’re dominated by perennial plants, with only a few annuals. Human agriculture, on the other hand, is dominated by annual plants, with only a few perennials. Supposing we could model our agriculture instead on these natural perennial plant communities – the benefits seem numerous. We wouldn’t need to till, to weed, to fertilise, to worry about soil loss or winter leaching and so on and so on. We would put less labour and less energy into our farming, and reap the benefits year after year.
So why don’t we? The literature sometimes presents the issue as a fateful choice made by our farming ancestors – a preference for domesticating annuals that, once made, was as if somebody had switched the points and committed us for ever after to the single track of a high input annual agriculture. There may be something in this. It’s possible to see why the early cultivators might have focused their efforts around annuals and then, with success, had few options but to stick with it. But this view troubles me because it fits within a narrative of modern progress and enlightenment that I frankly don’t believe – the view that our ancestors were less clever and less capable than us in spotting the possibilities for a truly sustainable and sophisticated perennial agriculture. It seems to me that if virtually all human agricultures have inverted the natural order of things by consistently favouring annuals over perennials in the long term, it’s likely due to strong underlying biological causes that are hard for agriculture to overcome, and not just cultural myopia.
J. Philip Grime’s book Plant Strategies, Vegetation Processes and Ecosystem Properties has given me a few inklings about what those causes might be. I can’t hope to convey the richness and complexity of Grime’s analysis here, but his basic point is that three fundamental plant strategies have arisen in response to three types of habitats – the ‘stress-tolerator’ strategy of a low nutrient-low disturbance habitat (think oak tree), the ‘competitor’ strategy of a high nutrient-low disturbance habitat (think nettle), and the ‘ruderal’ strategy of a high nutrient-high disturbance habitat (think chickweed). The fourth logical possibility – low nutrient-high disturbance – basically keeps plants at bay (think wind-blasted scree slope).
Most natural habitats in this schema are low nutrient-low disturbance, and even the ones that aren’t generally have a successional tendency towards it. The plants best fitted to cope with such habitats are perennial stress-tolerators with highly conservative life strategies. Nutrients are scarce, predators are legion, reproduction is risky – so stress-tolerators grow slowly, live long, reproduce cautiously (often clonally) and invest resources in making themselves unpalatable with prickles or poisons. Competitors and – more so – ruderals, on the other hand, prefer to make hay while the sun shines, investing in fast growth and prodigious reproduction at the expense of longevity and unpalatability. But they require habitat disturbance and/or high nutrient input to stave off the longer-term successional advantages of the stress-tolerators.
It’s easy to see where agriculture fits into this picture. Farming peoples want palatable and highly productive plants, and the way they’re most likely to get them is by interfering in succession and replicating ruderal/competitor situations of high disturbance and high nutrition by tilling and fertilising. The result is an agriculture based around prolific, tasty, leafy and/or seedy, mostly ruderal and mostly annual plants.
Grime’s three types are in some sense abstractions, which admit to hybrid strategies in practice. But there are still strong morphological barriers – it’s hard to be stress-tolerant and quick-growing and palatable. Human plant breeding efforts no doubt can and have pushed hard against some of these barriers, but I suspect we’ll struggle to overcome them altogether. For example fruit trees can be quite stress-tolerant, quite productive and certainly palatable – but they’re not very stress-tolerant, and their productivity has probably arisen through co-evolution with fructivorous animals as a reproductive strategy to disperse seeds a long way from the parent plant, which is no doubt why orchards are so disease-prone, and why organic orchards have been described as “the most challenging frontier an organic grower can face” (M. Phillips The Apple Grower). Likewise, most productive herbaceous perennials seem to be pretty short-lived – competitor hybrids, perhaps. Wes Jackson, probably the best known exponent of breeding for a perennial grain agriculture, reckons that it may take at least 50 years to breed a commercially viable perennial grain crop, but he points out that even if we were to develop only one it would pay dividends (Jackson, New Roots For Agriculture, pp.102-8).
I’m sure it would, and I’m sure that professional and amateur breeders should be devoting themselves more fully to the task – especially in places such as Jackson’s native Kansas where the effects of annual tillage agriculture are so manifestly destructive. But I suspect that it will be challenging. Jackson’s oft-quoted remark that “if your life’s work can be completed in your lifetime, then you’re not thinking big enough” maybe hints at his own sense of the difficulties he has embarked upon.
So where does all this lead? For me it suggests that we should support efforts to breed productive perennials – especially seed-based macronutrient-dense perennials – wherever we can, because annual tillage agriculture is pretty destructive. But it also suggests we shouldn’t bank on these efforts succeeding. It suggests that there may be a lot of good reasons for planting gardens packed with fruit and perennial vegetables, but we shouldn’t (yet) delude ourselves that these are ‘permaculture’ gardens unless we can live off them entirely without any surreptitious visits to the bakery or the chip shop (though talking of chips, a long hard look at tuberous perennials may pay dividends). For me personally, I think it means that I want to devote the majority of my farming efforts to figuring out how to grow annual crops as sustainably as I can, for example through agroecological potato growing, rather than going too far down the perennial route. Because much as I’m enjoying this perennial-intensive time of year, with all those lovely creamy spaghettis con asparagi and rhubarb crumbles, sadly it’s the spaghetti and the crumble rather than the asparagus or the rhubarb that are mostly responsible for keeping my hunger at bay. Oh, and maybe the cream as well…which of course brings us back to grass, probably the most successful perennial agriculture we’ve yet devised.
Successful it may be, but sadly an agriculture based around perennial grass isn’t successful enough to feed a planet of seven billion, at least without falling back on other aggressive ruderal strategists – such as Triticum or the notorious Glycine max. And this raises interesting questions about ‘productivity’. Since we devote a huge proportion of our croplands to livestock fodder, could we perhaps afford to push a little less hard at the productivity boundaries likely to trip up perennial grain culture if we adopted a more vegan diet? Maybe, but would it be enough? Everything points to perennial agriculture working best in low population, dispersed, intensive food gathering situations – in other words something barely resembling agriculture at all, so much as the preagricultural situation from which our early farming forebears emerged.
In Permaculture One, the founding document of the permaculture movement, Bill Mollison and David Holmgren wrote that “Permaculture, unlike modern annual crop culture, has the potential for continuous evolution towards a desirable climax state” (p.7). I think that may prove to be pretty optimistic in the face of the biological realities surrounding plant strategies. Any thoughts?
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Although I agree with much of what you said here I wonder if maybe you shouldn’t be so hard on perennials. The biggest annual world production by weight of any food plant is a perennial – sugarcane. Other perennials in the top 10 are potato, oil palm and tomato. A list of 10 major staple crops has 4 perennials – potato, cassava, yams and plantain. Interestingly the domestication of the perennials has often overcome issues of toxins and bad flavour and resulted in cultivation as annuals the potato being an example of both. Our ancestors seem to have managed to domesticate anything they needed to. Two of my favourites – coffee and grapes- are perennial and almost all fruits are perennial. So perennials provide much of what makes life good.
I mention all this because I would urge you to consider an approach where the potential advantages of perennials are allowed to show themselves in some sort of mixed system which allowed for the possibilities of further efficiencies in the overlap between difference zones of your farm. You previously mentioned, pollarded pasture, pigs and poultry in woods and forest gardens rather than orchards as examples.
Thanks Paul – yes I’m certainly not suggesting that there’s no place for perennial crops in sustainable farming. Most of our holding is down to perennials and long may it remain so. And I agree that perennials provide much of what makes life good. What I was questioning, though, is how easy it’s going to be to achieve that holy grail of sustainable farming – high-yielding perennial staple crops. The ones you mention are interesting, all being tropical crops, which was a dimension I neglected – perhaps my comments are more applicable to cool-climate agricultures. Nevertheless, I wonder whether they don’t still apply to the crops you mention. Cassava is pretty toxic after all, and sugar cane requires an awful lot of processing (though it’s clearly productive – another grass C-strategist I guess…but I suspect it’s widespread global cultivation has a lot to do with the lure of biofuels). I don’t know that much about these crops, but I think yields are on the low side, though that could be because they’re mostly peasant horticulture crops which haven’t had the intensive development of most agricultural crops – which brings us back to the point I made about perennial horticulture rather than agriculture. And interestingly, it seems that perennial staples like plantain, cassava and of course potatoes are generally treated as annuals either because of cultivation requirements or because yields are better that way (short-lived perennials, hybrid C-strategists). I’m sure you’re right that people have generally figured out how to domesticate whatever they want including many perennials, but my larger point was to suggest that plant-breeding still has to work within intrinsic morphological constraints. Fruit is a case in point – the more we select for high yield and good taste, the less perennial and the less stress-tolerant fruit trees seem to become.
Hi Chris,
Thanks for introducing me to CSR theory. I’m still getting my head around it and don’t have a copy of the book. From my little reading of online papers I see that competitor plants contain perennial trees, shrubs and herbs, whereas ruderals are exclusively herbaceous annuals. I take it that your example of nettle as a competitor must refer to the perennial one U. dioca — we mostly get the annual U. urens here in Australia which would be more of a ruderal. Grimes describes the form of competitors as typically “high dense canopy… extensive lateral spread above and below ground”, with “robust, often mesomorphic” leaves in his 1977 paper. So I wonder if you consider that perennial nettle is really a poster-child competitor? I imagine most plants native to the wet tropics as fitting the bill of competitors, but then they often have shallow roots. I guess what I’m asking is, do you know of anywhere there’s an accessible list of iconic competitor plants so I can help get my head around this category.
Also David Holmgren has just written an article which isn’t published yet, I’ve just been editing it, where he talks about our native bunya bunya trees and the drought resilience of oaks in Central Victoria restoring a bit of his 1970s naive optimism about producing human food and animal fodder with tree crops on some of the really tough and infertile (high stress) regions of Australia. Since sugars and starches aren’t nutrient dense there seem to be some outliers — plants which can produce half-decent crops in these kinds of high-stress environments. Not always with much regularity unfortunately.
Cheers, Adam
Adam, thanks for that comment and interesting questions. I’ll try to answer it soon – please bear with me, I’m a bit snowed under just at the moment!
Hi Adam
A brief attempt to answer your questions:
Yes, the nettle I was referring to was U. dioica. Grime’s specialism is grassland (especially the low nutrient calcareous grasslands of northern England), in which context I guess the nettle would fit the bill as a competitor in relation to those various properties you list.
Off the top of my head, the competitor properties that Grime characterises are high nutrient – low disturbance situations, and the resource strategy is one of quickly grabbing available resources, so again those properties fit the bill. I’ve only read two of Grime’s publications: his book Plant Strategies, Vegetation Processes & Ecosystem Properties, and his co-authored book The Evolutionary Strategies That Shape Ecosystems. The first one reports on his English grassland research, and so the species lists are very focused around that particular example. The second one extends the framework to animals and looks at it in global context…but I can’t seem to locate it on my shelves so will have to get back to you on the details. The basic competitor strategy is to be good at going out and grabbing resources when they’re available, but to be poorly adapted to disturbance or nutrient stress. U. dioica seems a good example inasmuch as you see it soaking up the nitrate runoff around the edges of cultivated fields, but you don’t see it much in the fields themselves, or in mature woodlands. Animal examples of competitor resource grabbers are whales and sharks, with ambush predation figuring more strongly among stress tolerators.
As a non-botanist I’ve found Grime’s work tricky to follow in places, and frustratingly silent on the implications of his framework for cultivated crops (though he did confirm in an email he sent me that he thought my inferences were correct). I think he’s well regarded among plant ecologists, and though his framework now seems possibly a little mechanistic for some people’s tastes, it does I think accurately define the life strategies and tradeoffs within which organisms have to work – hence my scepticism about breeding highly productive perennial staple crops, at least outside of the wet tropics.
Your comments on David Holmgren’s paper are interesting. Not sure about sugars and starches not being nutrient dense…surely the opposite is true?? But I think you’re right that there are some outliers, which may be amenable to useful breeding work. The problem as I see it in temperate climates is that there’s a basic tradeoff between perenniality and yield and it’s very difficult to optimise both – most plant breeding to date has merely augmented the existing ecological tendencies of the original plant. I’ve read quite a lot of the papers by the folks at the Land Institute and I just haven’t been convinced that they can overcome this. But there’s certainly scope as you say for low yielding perennial tree crops and cereals, or dual purpose forage/seed crops.
Hope that’s helpful.
Chris
Hi Chris,
Thanks for taking the time to respond. That makes sense about U. dioca that it fits into the competitor strategy. I’m still getting my head around the typical forms of the group, but getting there i guess.
Oops, I should have said starches and sugars (and I believe oils too for that matter) aren’t dense in *minerals* — they are essentially made of air and water, so even when a plant runs out of soil nutrients, it may slow its own growth but continue to produce crops of these things. I was thinking how eucalypts, as well as stunted heathland plants, can produce quite a lot of nectar. Agaves and prickly pear are some other examples that can produce a fair amount too in dry conditions in what i assume to be nutrient poor soils. I’m thinking that the type of stress might be pretty important. Shade is a more fundamental limiter on productivity at a thermodynamic level, but shade tolerant plants are more likely to produce low-energy, nutrient-dense food (albeit slowly) e.g., sorrel.
I saw on the PRI thread that Prof Grime had approved of your extension of his theory to crops. Nice one!
Also, I’ve just started watching this, Professor R. Ford Denison author of Darwinian Agriculture doing a lecture series on YouTube, who’s book you recommended on the PRI thread.:
https://www.youtube.com/watch?v=wX9pI8u4GZM&list=PLNowyW0S1hI8GsRZ_RZNcECgH-TPJhrjt
He talks about trade-offs too, which I’m finding useful and intuitively obvious.
I can think of a counter example to a trade-off from a cropping perspective (I think it fits within his framework): One reason stress-adapted plants (although I don’t think this applies to shade tolerant ones) are less easy to turn into crops is because they have evolved to be more toxic to animals on average. But I believe tagasaste evolved on the Canary Islands with low herbivory, so compared to its broom relatives, it produces a very palatable fodder, and although it’s probably not considered an extreme stress-tolerant plant, it can grow in fairly dry conditions, on nutrient poor soils. Possibly because it produces less toxin, it seems to grow more vigorously than it’s broom relatives too. So as a hypothesis, there might be, for instance, potential for humans to breed tanins out of oaks, and actually increase production. (I don’t know if tanins have much of a metabolic overhead though so it might not be a good example.) Although, we may need to protect the crop from more herbivores who find it more palatable, which would be consistent with what you’re saying, there would be a trade-off in that way.
Anyway, thanks again for your thoughts.
Hi Adam
Thanks for those very interesting comments. Good point about the low mineral requirements of starches and sugars…perhaps there are some complications here, however. For example, a lot of staple cereals are quite high in protein, which I’d guess would imply a high nitrogen input from somewhere. Also, there’s the issue of the lifecourse strategy – with perennials investing in organs of perennation over seeds and, as you point out, defence against herbivory, the result I suspect makes the cost/benefit equation for human use less favourable than with annuals, unless they’re bred to have more annual-type traits…but then that would probably lead to them being more like annuals, which seems to have been the result in a lot of perennial grain breeding efforts, and undermines the original purpose. I’m sure you’re right about identifying less toxic perennials and breeding from them, but also right that this leads to tradeoffs with pests (and also with the development of shorter-lived competitor/ruderal type traits – this seems to be the case with the bitter and sweet cassavas, for example). The question would then be what the optimum tradeoff between the ecological effects of annual/perennial cultivation and the yield effects in terms of perennials & ruderals and pest susceptibility. Interesting.