The Little Karoo has patches of calcareous soil among the low hills where topsoil is largely washed away, exposing calcrete. In spite of the initial barren appearance of some calcrete patches, small plants of interest may be spotted in pockets of retained soil, often rare ones seeking the particular mix of soil nutrients and cohabiting effectively with a variety of other plant species.
Where calcrete based soils have the Karoo plant, Pteronia pallens, known as the Scholtzbos growing in it, however, few other plants are seen, as the Scholtzbos demolishes its competition.
The phenomenon is known as allelopathy, a form of species domination on a patch of ground, involving the production of certain biochemical substances that prevent the establishment, survival or reproduction of other species. The appearance of competitors can thus be suppressed, similar to the weeding that farmers do for maximising growth of their crop plants.
Allelopathy may also be positive insofar as some plants, fungi, algae, corals or bacteria exude chemicals that enhance the metabolism of certain other species, as in choosing your neighbours or creating a private garden for a better life (Vlok and Schutte-Vlok, 2010; Wikipedia).