Interplay among self-thinning, efficiency of space occupation and biodiversity in terrestrial plant communities

Abstract Biomass-density relations have been extensively studied for monospecific plant stands, leading to the self-thinning law, Interspecific Boundary Line and efficiency of space occupation. Later, came experiments with mixed-species stands testing the effects of biodiversity on productivity. Here, we test biomass-density relations in natural plant communities. The biodiverse stands were subject to a community self-thinning. Furthermore, biodiversity promoted efficient space occupations. However, as these biodiverse stands approached their maximum biomass packing, fierce competition for space eliminated the weaker individuals and species. In the background, water availability mediated the strength of this interaction. These results fit the unimodal biodiversity-productivity relationship, as well as the ‘intermediate disturbance hypothesis’ but with the environment varying over time instead of space, and can unify apparently contradictory past evidence. The efficiency of space occupation used as an ecological indicator further helped understand the interaction between an invasive weed and the autochthonous community, as well as the benefit brought-about to a specific species assembly developing from within a mat of dead lawn. The latter denies Savory’s holistic management theory stating that the desertification of grassland in Africa and elsewhere resulted from the accumulation of dead plant biomass occupying space otherwise available for the growth of new plants.