After posting about nettles and docks, I got to thinking about brambles (Rubus fruticosus) and bracken (Pteridium aquilinum) as well. Also mint (Mentha arvensis) which we have in abundance and which spreads in a similar fashion, and mimosa (Acacia dealbata) which we don’t have on the quinta but which is another “problem” plant in Portugal. All these plants are vigorous, resilient and quickly outcompete most other herbaceous species. The primary means of their rapid spread and apparent monocultural tendency are their extensive creeping rhizomatous root systems.
Nettles, brambles, bracken and mimosa
What I was thinking about was what do all these plants have in common besides these characteristics? What’s their role in nature? Is there an analogous process we can easily relate to that’s more useful and true to the state of things than this notion of “noxious weeds”?
The first thing that’s apparent is that invasive species are responses to disturbance: to the soil itself, or to its chemical/mineral balance (nettles grow in response to nitrate pollution as much as to ground disturbance; bracken, brambles and mimosa grow on impoverished and exposed soils). These species very quickly form a dense network of fibrous roots over a disturbed area like nothing so much as the strands of fibrin in a blood clot forming across an open wound. Their vegetative growth above the surface becomes equally thick and impenetrable, deterring further disturbance by sheer physical presence, thorns, stinging hairs, or toxicological agents (like bracken’s cyanogenic glucosides which precipitate rapid respiratory failure in grazing animals).
While doing their utmost to prevent further disturbance, these species work hard below the surface to heal and condition the soil. Rhizome growth rapidly breaks up compacted ground (bracken, brambles, mimosa) or forms a particle-accumulating mat in waterlogged areas (mint). Depleted soils have their fertility restored by nitrogen fixation (mimosa, gorse, broom and other members of the Fabaceae/Leguminosae), mineral accumulation and copious amounts of rich humus (nettles, bracken, mint). Their leaf litter also helps restore soil structure and provide a protective mulch preventing excessive moisture and mineral loss, and allowing the recolonisation of the soil by all the various invertebrate species that help break down the litter, creating and maintaining a healthy soil ecology.
Mint, brambles and nettles coexisting on our middle terrace
As time passes and soil vitality and health is restored, species diversity increases. Deep-rooted herbaceous species which can penetrate the thick rhizomatous layer take hold, trees grow, and these ‘clotting’ species become less dominant, to be succeeded eventually by the natural climax vegetation of the area.
There’s a widespread tendency to see these plants as “invasive”, “destructive”, even “evil”, “monstrous”, something to be waged war on, battled, exterminated. That’s a nonsense — rampant (Jungian) projection on the part of humankind. It’s not the plants that have these qualities so much as the human assault on nature which creates the conditions requiring their intervention. And as for “taking over”, as David Theodoropoulos writes, “the fossil record is clear – invasion increases biodiversity (Cornell & Lawton 1992), and the experimental record indicates that the greater the rate of invasion, the higher the diversity of the resulting assemblages (Robinson & Edgemon 1988). As Turner (1996) stated, “life evolves at the edge of chaos, the area of maximum vitality and change.””
How to work with them rather than against them when their very nature is all about keeping the likes of us well away? Well there’s the challenge. Don’t wound the soil in the first place would be the obvious conclusion.
Back to Masanobu Fukuoka: “If we throw mother nature out the window, she comes back in the door with a pitchfork.” His no-till methods are something I’m becoming more and more convinced about and intending to follow.