Posts Tagged ‘soil fertility’

Fertility – Less or More?

June 22, 2012

A few of us have been discussing, among other things, soil fertility, pastoralism, deforestation, reforestation, agriculture (of course) and permaculture-type solutions for restoring the ecologies impoverished by this culture over on this Leaving Babylon thread. Here’s my most recent contribution on the topic of soil fertility vs. conservation:

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I’ve been thinking lots lately about this issue of soil fertility. On the one hand we’re living through a period of extraordinary fertility thanks to the nitrates and phosphates in petroleum-based fertilisers – ‘more atmospheric nitrogen is fixed by man (as fertilizer) than by all natural sources combined’ (Ken Thompson, No Nettles Required, p.160) – and all gardening and farming is geared towards maintaining or increasing this. And on the other hand we have a legacy of plant and animal species uniquely adapted to the impoverished soils resulting from hundreds/thousands of years of intensive, organic farming, grazing and forestry; a biodiversity that dies out when the soils get too fertile or specific management practices are discontinued. Here’s Michael Allaby writing in the Woodland Trust’s Book of British Woodlands:

The trees that are coppiced regenerate and go on regenerating for a very long time: far from injuring them, coppicing seems to extend their lifespans, so they become an almost perpetual source of wood. Chemically, the wood is composed of substances obtained from the air and soil, like any part of any plant, and cropping removes those substances. Livestock grazing among the trees returned some plant nutrient, but they, too, were removing vegetation by their grazing. The overall effect is a slow but steady export of plant nutrient and a decline in the fertility of the soil. This makes it sound as though the coppicing system is harmful, but harmful to what, or whom? Some plants are better than others at exploiting rich supplies of nutrient. Feed them well and they grow vigorously and, in relation to the plants around them, aggressively. On a fertile soil, therefore, the natural succession by which plants colonise an area will proceed fairly quickly to a situation in which a small number of aggressive species dominate the vegetation.

On a less fertile soil this cannot happen, because the aggressive species are denied the nutrients they need for more vigorous growth. This allows the less vigorous species, with more modest requirements, to thrive. The final result is a great diversity of plant species. The ecological rule-of-thumb is that the greater the fertility of the soil, the fewer plant species will establish themselves on it; and if you prefer a great diversity of species you need a poor soil. Over the years coppicing produces poor soils, and so coppiced woodlands tend to have a rich diversity of plant species. The greater the diversity of plant species, the greater will be the diversity of animals feeding on them, and since the arrival of herbivorous animals is followed by the arrival of predators and parasites of those animals, the entire ecosystem is enriched. (p.106)

So what direction do we pull in? Obviously the petro-fertiliser era is a blip which is going to end in short order, yet I’m less-than-convinced about the longterm viability of the systems that preceded it. Intentionally working to impoverish the soil? Surely sooner or later that will starve the ecosystem to death (although I’m not aware of any coppice rotations that have been stressed to breaking point in this way, even when supplying charcoal for industrial purposes). I think I agree that we have a responsibility to do right by the species we’ve in effect provided the selection pressure for over all these centuries of domesticating the landscape, whether that’s helping them adjust to the changing circumstances or, if that’s not possible, allowing them to die out with dignity. But I think the conservationists are wrong about greater fertility equating to lesser diversity. Maybe this would be the case in the short term, but after a while I expect it will simply be a different kind of selection pressure leading to an explosion of diversity in the more nutrient-hungry plants. How many different hybrid forms of Bramble, Nettle & Dandelion are there already in existence?

Fire-setting is another case in point. From what I’ve read it sounds like N American Indians burned grasses and forest understory purposefully to release the nutrients locked up in the standing dead plants, changing them into a form that was bio-available to the herbs, shrubs and annuals that would be growing on that spot by the next season. This was also an active selection for plants that provided edible, medicinal and other uses for the Indians (and, I assume, for the wildlife they shared the habitat with). It would be interesting to know the mix of woodland plants in Paleo/Mesolithic NW Europe – whether fire management caused this to differ in a similar way. A local conservationist has told me to look for Nettles and Brambles growing in places where our group had previously set fires in old coppice woodland, due to the nutrients released in the wood ash.

Over all it seems to be the case that humans are associated with enriched fertility in soils. That’s one line of archeological evidence for habitation by prehistoric man – at least in Europe you find seeds or pollen grains of Nettle, Plantain, Goosefoot and other associated ‘weeds’. We pitch camp somewhere for the season, eat, shit, do some burning and maybe a bit of gardening before moving on. My best nettle crops have come from places disturbed by people (the very best being where those people fenced off special areas in parkland for their dogs to come and do their business in the times before the ubiquitous small black plastic bags – mmm, dog poo nettles…) Anyway, the main problem with coppicing and other woodland management seems to be the same old civilisational problem of exporting resources far away from their point of origin. If people lived in the woods, building homes, cutting fuel, crafting necessary artifacts from the trees around them, and letting it all rot down on site, I think that could lead to a thriving & enriched ecosystem, supportive of a wide variety of plants and animals.


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