I posted a while back on the issue of annual and perennial plants and the permaculture movement. An interesting debate on the Permaculture Research Institute of Australia website initiated by Angelo Eliades has prompted me to reflect further on the question.
Other than confirming once again that the Y chromosome finds ever new arenas in which to construct its fragile ego, the debate turns on the possibilities for replacing the widespread cultivation of annual plants in global agriculture and horticulture with perennial plants. As explained in my original post and as further outlined in Eliades’s article, the potential benefits of doing so are multiple. The question is whether it’s possible to provide enough nutrients – particularly macronutrients such as energy and protein – to the planet’s vast human population with a purely perennial agriculture.
It’s striking that most wild floras are dominated by perennials, whereas most agricultural crops including the major staples are annuals (wheat, rice and maize provide the majority of global macronutrients). But there are some perennial staples – mostly tuber crops such as potatoes, yams and cassava, although very often these are cultivated as if they’re annuals, thus losing most of the environmental benefits of perenniality. It’s also worth pointing out that since the Neolithic revolution, most of the world’s population has been fed by annual grain agriculture including all of the famous ancient civilisations, with tuber/perennial-based systems dominating in only a few areas such as New Guinea and parts of sub-Saharan Africa (see, for example, Mazoyer & Roudart A History of World Agriculture or Mithen After the Ice). But though relatively rare, these tuber-based systems have proved stable and successful.
Now, an important permaculture principle is to model human landscape design after natural systems, and since perennial plants are so dominant in the wild this alone is enough to make many permaculturists favour perennial-based cultivation. The puzzle then is why it’s proved so relatively rare in human agricultural history. Eliades believes, first, that perennial plants are more productive than annuals, while simultaneously requiring less energy and effort to grow, which would make the puzzle all the greater if it were true. His answer is that, second, the only reason we plant annual crops is because of “arrogance and lack of perspective”.
Both of these claims are so absurd that they shouldn’t really require any refutation. To fabricate a cultivation system that conjures additional productivity out of nothing, while simultaneously dishonouring the many annual-based farming cultures that have laboured to create viable social ecologies takes a lot of cheek, and is the sort of thing that prevents the wider world from taking permaculture as seriously as it should. OK, perhaps I should register one slight qualification here – as I mentioned some time ago in my post on potatoes, it’s possibly true that grain-based agricultures better suit the interests of state-building elites than tuber-based horticultures (though I very much doubt it’s really that simple), so in that respect perhaps there may be a small role for ‘arrogance’ in the development of annual cereal culture, but not nearly enough to explain its ubiquity.
So we’re back to square one with the puzzle of annual agriculture and perennial flora. In my earlier post, I mentioned Professor J. Philip Grime’s CSR theory as a way to explain the puzzle. Grime classifies plants as ‘competitors’ (selected for in high nutrient – low disturbance situations), ‘stress tolerators’ (low nutrient – low disturbance) and ‘ruderals’ (high nutrient – high disturbance). Most wild habitats are low nutrient, low disturbance and are characterised by stress tolerator perennials, with slow growth rates, cautious reproductive strategies and defences against herbivory, all of which tend to make them less appropriate for domestication in terms of yield and possibly palatability.
As Paul Hillman pointed out in a response to my original post, and as Angelo Eliades also points out, there are nevertheless quite a number of highly productive perennial crops such as sugar cane, cassava, plantains, potatoes etc. With my thinking clouded by the perennial vs annual distinction in the context of CSR theory, my initial response was to suggest that these crops were probably less productive than the annuals. Quite how productive they are in terms of yields per unit fertiliser input or per unit solar input in comparison to the major annual crops is something I need to work on some more, but I’ll now readily accept that they might well compare favourably. Because on reflection, the broader point about all of these perennial staples is, I suspect, that they fit naturally into the ‘competitor’ category of high nutrient/low disturbance crops – essentially pioneer plants that quickly occupy and crowd out fertile space (think of the way gardeners describe potatoes as a ‘cleaning crop’, for example) before giving way to stress tolerators in long-term succession. Many woody fruit and nut species also occupy the competitor or competitor-stress tolerator hybrid niches, as Grime has remarked. In this respect, perhaps we can place the three strategies on a continuum of agricultural usefulness (yield and perhaps palatability) from R to C to S. And if we map the annual-biennial-perennial distinction onto that continuum we’ll find most of the annuals and biennials and a few of the perennials at the R/C end of the spectrum, and most of the perennials at the S end.
That, at any rate, is my working hypothesis. It explains why agriculture and horticulture tend to favour R and C strategists and invariably try to prevent ecological succession (by ploughing, mulching or burning), and this in turn explains why our cultivated plants are mostly annual and biennial but with a number of important perennials.
All of this matters because C strategists – whether annual or perennial – are essentially short-lived, high nutrient demanders, so they don’t exempt us from the fundamental agricultural tasks of generating fertility and preventing succession. This shouldn’t be all that surprising, because in the spartan energetic economy of nature, nobody can expect a free lunch. The more we try to push productivity, the more we need to fertilise and curtail succession, and the more perennial agriculture starts to resemble annual agriculture (eg. with sugar cane replanted every second year in high output systems). And unfortunately we do need to push productivity, because there are 7 billion people on Earth. I think it’s worth being a little sceptical of anyone who claims to grow all their own food, and even more sceptical of anyone who claims to grow it all from perennials – which is not in any way intended to suggest that I think it’s a bad idea to try. There’s much to be said for abundant polyculture, but we do need to keep an eye on overall yield and energy balance. In that respect, every step towards a more perennial staple agriculture and horticulture is important, and initiatives such as the Land Institute need our unqualified support. But the ultimate goal of a productive perennial agriculture is not an easy one to achieve – to state otherwise on the basis of a simplistic reading of permaculture principles risks discrediting the movement. There’s already far too much snake oil on sale.
I have a lot more work to do to flesh out this basic thesis, but I think that’s enough for now. I’d be interested to hear anyone’s further thoughts on the topic.