It is often considered a good practice to not led weedy species go to seed. This is suggested as a way of preventing the accumulation of viable unwanted seeds in the soil, reducing our requirements for weeding in the future. However, there seem to me several reasons why this is not a necessarily a wise practice. Couldn’t it simply encourage a different type of more vigorous weeds in the soil (such as those that propagate rhizomatically or through seeds that are blown in from a far distance)? And won’t this greatly reduce the diversity of the natural community and the biodiversity potential (and therefore, at the very least, the resiliency) of the land, and encourage the most pernicious weeds at the expense of those whose spreading requirements are more exacting? In particular, wouldn’t the number of leguminous species likely go down, and with it an important player in the self-sustaining potential of the land?
In my garden, there are no weedy species that I don’ let seed, though I don’t let all of every species propagate. But my goal is not extinction and my criteria not genocidal: I instead look at relative abundance, edibility, allotropy, medicinal value and lighting effects. A note on the latter: I believe the spread of Cyperus rotundus is due to a vigilant effort to destroy all weeds without considering how some are capable of blanketing this difficult species from the sun. I have personally experienced a crash in Cyperus stands solely through maintaining a Synderella nodiflora groundcover (whose glass slipper I’ve now found), which emerged naturally after I let it. I suspect that weeds themselves will be our most faithful, long-term weedkillers (as well as our ploughs and fertilizers) should we decide to eventually become a species for whom sustainability means something sustainable. Trees are often enlisted, and may be appropriate assistants against some species such as Imperata that are too tall to be smothered, but it seems to me that our first line of defense is often overlooked.
It is the machete and the sloping land that favour a continued relationship with our plant community by physically preventing the possibility of local botanical holocausts. The rate of destruction is slow enough and the possibility of complete success remote enough, that the resource-poor farmer is fated to having to live with weeds. This means that every possible use of each weed sharing land with our crops is of highest importance. It is no coincidence therefore that these farmers are those with the greatest botanical familiarity (and 2,4-D dispersers, the least) with these plants. But their knowledge is far from complete and should be looked on as a system co-evolving recursively with the evolution of the farmer’s context –in this case, the field. For example, the edibility of a weed is by no means conclusively established by indigenous folk in an area. There are even some weeds that are considered inedible in one part of Laos but sometimes consumed in another, such as Crassacephalum crepidioides, which I’ve yet to hear of eaten in the North. My favourite example though is the wild Celosia. This plant is collected and sometimes even grown as a vegetable food in many African countries, but in this part of Asia it is routinely cleared to make way for Brassicas and other familiar greens. It tastes benign, is easy to incorporate into many dishes and has beautiful flowers that are often visited by various species of predatory wasp. It also has a long non-woody taproot that probably provides quick channels for water inflow after its annual floral exuberance has weaned and it withers its way towards transformation. I can’t think of a better food candidate for a post-industrial dinner table. This year, I will collect the seeds of this species and broadcast them in a plot as a vegetable, alongside all the villagers growing their strips of picky mustard greens.
The idea that these weeds are invasive species not “supposed to be here” is both dangerous and false. It is dangerous because it pits purity against contamination in a Hitlerian judgment that leads us to think of some species as “bad” and requiring extermination in order to regain a now tarnished Eden. It is false because it is based on an incorrect conception of ecosystems - and idea that ecosystems were, before humans, in some sort of idyllic harmony. In fact, the dynamism brought through the migration of species, by wind, by floating, by piggybacking on others, has probably propelled the evolution of species and has made many beautiful and interesting species what they are today, as the pine beetle would surely help the pine if eventually allowed to fulfill its destiny undisturbed by human management. In the end, it is inevitable that these great swaths of forest, gradually depending on more and more human interventions, eventually become so separated from their environmental contexts that they become weak and wholly dependent creatures, and surely a much greater long term danger than their being attacked at present volumes. If villagers have discovered medicinal and other values for introduced weeds, it is just as probable that other species have also now found some use of them and have accepted them into the biological community stewarding the land. This does not mean that other potentially invasive species should be let loose without abandon. Novel species in established ecosystems do cause shifts in other members of the community and in some cases displacement and extinction. But, be the time we’ve noticed it, the transformation is already well underway. What it does mean is that we realize that we can’t go back in time without huge sums of money and energy in order to solve a problem that Mother Nature solved already, when she fixed it so that, as the permaculturalists realize, “the problem is the solution”.
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