Timothy Crews and Lee DeHaan (henceforth, C&D) of the Land Institute have written the above-titled paper1 in response to my paper ‘The strong perennial vision: a critical review’2, which I’ve discussed in my previous two blog posts. As mentioned in those posts, C&D provide this threefold characterisation of my argument:
- Ecological theory suggests that perennial grains may yield less than annual grains
- Strong criticisms of annual agriculture are unfounded, both socially and ecologically
- Focus on perennial grains detracts from more important strategies for achieving agricultural sustainability
The first of these points is much the most important, and that’s what I’m going to focus on in this post.
C&D versus CSR
C&D’s main gambit is to suggest that Grime’s CSR theory (described in my previous post) is a general framework for understanding plants in their habitats, which becomes misleading when it’s applied in the manner I use it to specific plants, particularly plants under artificial selection. There’s some force to the first part of this objection. There’s continuous variability of plants across multiple traits, not complete segregation into C, S or R types. And, certainly, there is no cast iron law of ecological logic that demands augmentation of one trait must inevitably lead to the diminishment of another. So possibly it’s true that I use the CSR framework in too general a way, and that I interpret tradeoffs too stringently.
But though the CSR framework is indeed a generalising one, Grime himself and me in my usage of his framework do focus on two specifics: resource availability and disturbance. By contrast, C&D in their discussion of ‘stress tolerance’ invoke it in a very much more general sense to mean anything that stresses the plant. Then they go on to have some fun at my expense by using the framework very specifically in order to identify various complexities of stress tolerant, ruderal and competitive traits that transcend the annual-perennial divide, and of the existence of high resource (but non-seedy) herbaceous perennial systems.
In my view, it’s best not to fixate on ‘perenniality’ as such but instead to examine the covariance of traits like longevity, sexual allocation etc. So I’m not sure how much of C&D’s discussion here is relevant to my arguments, and I’m not sure how much they and other Land Institute authors really understand the relationship between resource availability, disturbance and sexual allocation. But yes I concede that there’s plasticity of plant traits with which plant breeders can work. How much? In C&D’s opinion, a lot: whereas I posit a tradeoff between augmenting stress-tolerant traits (low resource input, individual survival) and sexual allocation, they profess “no experimental evidence [of this] to our knowledge”.
So in C&D’s view, the CSR framework goes out the window and plant breeders have a free hand to work with the unique traits of given plant species which, through artificial selection, they can work up into whatever phenotypes they want. CSR theory, in this view, “does not address what happens if humans were to create a new type of habitat never before seen in nature”. The kind of habitat they have in mind, their ‘domestic prairie’ of perennial grains, is one that “requires the development of a never seen in nature environment with high resource availability, little tillage, and with strict human directed selection for maximum seed yield over several years”. C&D criticise me for misconstruing domestic prairie as something requiring little or no human inputs or management, and for being too hidebound in my thinking about feasible agroecosystems by the habitats that are actually found in nature. Instead, they invoke the authority of Professor Ford Denison who argues that “humans will likely have the greatest success in breeding for traits that were never previously selected for in nature”.
Of selection, natural and artificial
Let me try to work through some of this. First, it’s noteworthy to learn – despite all of Wes Jackson’s writings on ‘natural systems agriculture’ and the mimicking of natural ecosystems – that C&D’s programme turns out to depend on an absolute break with natural ecosystems more thorough than that of extant agricultures, and indeed unprecedented in the history of agriculture to date. That doesn’t necessarily mean it’s a bad idea or that it won’t work, but I think those permaculturists who enthuse about perennial grain crops as an example of nature mimicry might sit up and take note. Still, with Denison’s work as inspiration, C&D pursue a line of argument that’s certainly plausible: unaided by human hand, natural selection won’t necessarily find solutions that work well in agriculture for human purposes.
But let me pursue an alternative, more permaculture-oriented and nature-mimetic argument than C&D, with Denison once again acting as my guide. Perhaps natural selection hasn’t come up with seedy herbaceous perennials because such plants involve fundamental tradeoffs or contradictions which artificial selection will be unable to surmount any better than natural selection. Denison certainly thinks so – his book Darwinian Agriculture3 has a chapter called “What won’t work: misguided mimicry of natural ecosystems”. Its premier example is the Land Institute’s perennial grain breeding programme.
So it seems to me a little cheeky for C&A to invoke Denison in support of their programme. It’s true that Denison argues for the merits of breeding for traits not previously selected for in nature, but the sort of examples he uses (like short-strawed cereal varieties) are more consistent with my emphasis on pushing plants in directions they’re already predisposed to go in evolutionarily than in a contradictory push to increase both sexual allocation and individual survival.
If it’s true that through careful selection of plant traits crop breeders can overcome the basic biological tradeoffs encountered by wild plants, then C&D may be right that Grime’s framework is irrelevant here, that there are no fundamental obstacles to producing high-yielding, endogenous nutrient-cycling perennial grain crops, and that these plants will not be subject to existing ecological constraints. But I don’t think it is true. I take the point that there’s underlying plasticity and complexity of traits amongst plants that isn’t captured in a simple framework like CSR. In ecology these days, life history seems to trump r/K or CSR. Citing Barbour et al4, C&D state “There are as many life history patterns as there are species…” Perhaps. There is always a scientific tradeoff between generalisation and particularisation. C&D try to have it both ways by invoking CSR theory in a very general way to refute the specifics of my analysis and in a very specific way to refute the generalities of my analysis. But to infer that there is no higher level ecological patterning of life history involves the mistake of not seeing the wood for the trees in an almost literal sense.
In his early work Grime adduced the CSR framework in relation to detailed studies of English grassland plants. In his more recent work, he’s applied it to the whole of the biota throughout the history of life on earth – whence his statement that the outcomes of natural selection are restricted “to a rather narrow range of basic alternatives in life-history, resource allocation and physiology”5. These are what Grime calls the ‘evolutionary strategies that shape ecosystems’, which are applicable to past, present and, one must assume, future ecosystems.
I’m not sure on what grounds C&D think the plants they breed can escape these evolutionary constraints simply by virtue of the fact that they have been artificially selected. That’s not the case with the current suite of artificially selected annual crop plants, which bear all the traces of those constraints ordained by natural selection – hence the whole problem of annual tillage agriculture. To me, C&D’s position greatly overstates the autonomy from Grime’s ‘narrow range of basic alternatives’ that can be achieved by artificial plant breeding. Sure, we can push the envelope with things like fertiliser and pesticide laced short-lived orchard trees propped up on sticks on dwarfing rootstocks. In their paper, C&D make quite a play against my view that the example of high input/output apple orchards isn’t a sensible prototype for a sustainable perennial agriculture and involves a hypostatisation of perenniality per se. But to my mind, the example of the intensive orchard exemplifies precisely the tradeoff problems associated with issues like survival, longevity, nutrient response and agroecosystem management that I explore in my paper in detail and that C&D ignore almost entirely in their response.
C&D say that there’s no experimental evidence for the tradeoff I posit between sexual allocation and perennial-type survival traits. Grime’s framework provides an experimentally-validated evolutionary and ecological context, while Peggy Wagoner’s 1990 review6, supplemented by various more recent studies I cite, is a veritable litany of artificially-bred perennial grain varieties that either survived well and produced little seed, or produced a lot of seed and survived poorly. In a blog post7, Land Institute breeder David Van Tassel explicitly acknowledges that perennial grains will be subject to various tradeoffs, and in my paper I explore the biological basis of these in detail – an analysis again ignored by C&D in their response.
The most compelling evidence C&D invoke to refute my suggestion of a sexual allocation–survival or longevity tradeoff is a study of sunflowers in which ‘early successional perennials’ had a higher sexual allocation than annuals. Well, nature is never quite as orderly as our models of it, but I can’t say I find a slight anomaly of this sort across longevity or R-C-S trends hugely undermining of my basic argument, and as I’ve already said CSR may be a better way of thinking about the issues than annual vs perennial. I’d like to know how long-lived the high-allocating early successional sunflowers were, their survival rate, whether they exceeded annual allocations in every year of their lives, and whether the studies controlled for allometry. Unfortunately, I’m unable to access the relevant paper, but its abstract states “A number of studies have tested whether reproductive effort (RE) is correlated with successional maturity; in these, annuals generally had higher RE than herbaceous perennials (29 and 13%) and RE in herbs often diminished as succession progressed”8. On the face of it, this looks to me more confirmatory of my arguments than of C&D’s.
Probably the best experimental evidence for the difficulty of breeding perennial grains that can match the yields of annuals is the fact that nobody has managed to do it in at least 10,000 years of extraordinary agricultural achievement, and in over 100 years of professional, scientific plant breeding. Land Institute authors have written a paper that explains with some degree of plausibility why the first farmers were unlikely to have domesticated perennial grain crops9, but if the problem is mostly just a matter of coming up with the right set of traits to work with, the historic, global failure to have found them anywhere in the world at any time since seems to me quite a troubling issue for their line of argument. More plausible, I think, to accept Peggy Wagoner’s view: “the resources available for seed production in a perennial appear to be less than in an annual”6.
C&D describe the ‘domestic prairie’ that the Land Institute is working to develop as a “never seen in nature environment with high resource availability, little tillage, and with strict human directed selection for maximum seed yield over several years”, and they think I misconstrue the concept as something more natural and less interventionist.
Perhaps I am muddled about domestic prairie. I do find it a rather elusive concept. According to Wes Jackson it’s “based on nature’s ecosystems” and has something to do with “natural systems”10; according to C&D it’s that never-seen-in-nature environment and a high resource input agroecosystem where they “hope that as much as possible these resources can come from nutrient cycling and endogenous sources”; and according to Jackson and other Land Institute authors it’s something that’s going to end 10,000 years of conflict between agriculture and nature. Most annual grain farmers surely hope that “as much as possible” their nutrient inputs can come from endogenous sources too. How much is C&D’s “as much as possible” and what yields will be associated with it? The answer to that question is surely critical, but C&D don’t address it; instead, they studiously ignore my paper’s analysis of nutrient response, and invoke the misleading example of non-starchy and non-seedy forage and perennial biofuel crops.
At what point does ‘domestic prairie’ segue into ‘green desert’? When does ‘natural systems agriculture’ become plain old anthropogenesis? Would a polyculture of Roundup Ready® alfalfa and corn be domestic prairie? And how exactly is all of this going to end the conflict between agriculture and nature? In a recent post I criticised Mark Shepherd’s emphasis on nature mimicry in his ‘restoration agriculture’ project for its protean character, and I think the same is true of C&A’s domestic prairie. Basically these systems (probably all systems) mimic nature except where they don’t, and the concept of ‘nature mimicry’ then becomes essentially rhetorical.
The discussions around both perennial grain domestic prairie and Roundup Ready® domestic prairie seem to me to overstate the extent to which agricultural problems are reducible to plant breeding problems. In both cases, it’s as if agricultural problems can be solved purely or largely by genetic manipulation of plant traits without any messy ecology getting in the way out in the field. In the case of Roundup Ready® corn, that conceit is already belied by the emergence of Roundup tolerant weeds. With perennial grains, I think there will be different but no less daunting problems. These essentially revolve around the very narrow parameters involved in juggling high sexual allocation in a protein or carbohydrate rich seed crop with high perennation year after year, funded only out of longer-season photosynthesis, through the vicissitudes of weather and climate to produce agriculturally acceptable outputs within the ebb and flow of complex plant guilds, with no or at least ‘little’ (the distinction is probably quite significant) herbicides, pesticides, fertilisers or tillage despite their high resource demands. Before anyone starts talking about ending 10,000 years of conflict between agriculture and nature, I’d like to see some sound numbers put to those parameters.
I accept that there’s plasticity with which plant breeders can work, and if somebody could explain to me what domestic prairie really is I could probably be persuaded that it’s possible to develop a domestic prairie of decently yielding and decently long-lived perennial grains, though probably not as high yielding as annuals. In fact, I already accepted this possibility in my paper. But I’m not convinced that C&D and the Land Institute adequately emphasise the extremely tight parameters within which such a domestic prairie would have to operate and the tradeoffs it would have to reconcile if it’s to found a high-yielding low environmental impact grain agriculture long-term. And, as I’ll explain in my next post, I’m not sure a high yielding grain agriculture is such a great idea in any case.
1. Crews, T. and DeHaan, L. 2015. ‘The strong perennial vision: a response’ Agriculture and Sustainable Food Systems, 39: 500-515.
2. Smaje, C. 2015. ‘The strong perennial vision: a critical review’ Agriculture and Sustainable Food Systems, 39: 471-99.
3. Denison, F. Darwinian Agriculture, Princeton University Press.
4. Barbour, M. et al. 1987. Terrestrial Plant Ecology. Benjamin/Cummins.
5. Grime, J. and Pierce, S. 2012. The Evolutionary Strategies That Shape Ecosystems. Wiley-Blackwell.
6. Wagoner, P. 1990. Perennial grain development – past efforts and potential for the future. Critical Reviews in Plant Sciences 9: 381-408.
7. Van Tassel, D. 2012. Tradeoff or payoff? http://perennialgrainresearch.blogspot.co.uk/2012/11/biomass-accumulation-by-miscanthus-in.html
8. Hancock, J. and Pritts, M. 1987. Does reproductive effort vary across different life forms and seral environments? Bulletin of the Torrey Botanical Club 114, 1: 53-59.
9. Van Tassel, D., DeHaan, L., and Cox, T. 2010. Missing domesticated plant forms: can artificial selection fill the gap? Evolutionary Applications 3: 434-52.
10. Jackson, W. 2002. Natural systems agriculture: a truly radical alternative. Agriculture, Ecosystems and Environment. 88: 111-117