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Pioneer plants and their ecological role

Mon 24 Aug 2020

One of the tell-tale signs of historic overgrazing is bush encroachment by certain species of plants, like sickle-bush (Dichrostachys cinerea), blackthorn (Senegalia mellifera) and slender three-hook thorn (Senegalia Senegal). It is a lament of many a conservator, as it takes up habitat, shortens viewing distance of wildlife, and generally makes life difficult. But, very few people understand the role of these plants in our natural ecology. Nature has an amazing way of healing itself. An overgrazed patch of earth is like a wound—it is open, with little to keep the topsoil together, and sterilised by the sun. Of course, this loosens the soil, changes its pH composition, and makes it easier for the wind to blow it away, or for rainwater to wash it away, causing soil erosion. Pioneer plants are like a scab that forms over an open wound.

Pioneer plants thrive in poor soil conditions. They love soils with unbalanced pH. Seeds of these plants readily grow where nothing else wants to grow. Soon, stands of these plants form thickets, making it very difficult for animals to penetrate these areas. These thickets also provide shade, protecting the soil under them. The wind will blow other plant seeds, as well as fertile dust into these thickets where it collects and breaks down, thereby rejuvenating the soil and adding nutrients. The plant’s own leaves and twigs collect in the dense brush as well, adding to the detritus, and will eventually also compost, to add to the nitrification process. The root system also aids the soil by keeping it together, making erosion less likely. In time, the acidity of the soil becomes more balanced, aided by the nutrients and minerals released by the decaying plant matter, and the pioneer forms more woody growth, up to a point where the plant dies, usually because the pH has changed to such an extent that it is no longer suitable for the pioneer to survive in. The plant itself is then consumed, either by termites, wood borers or fire, releasing all the nutrients that it accumulated through its lifetime, back into the now rejuvenated soil.