Self-thinning of biodiverse plant communities follows the Intermediate Disturbance Hypothesis

Biomass-density relations have been extensively studied for monospecific plant stands in forestry systems, 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 plant communities to better understand their dynamics and application as an ecological indicator. The biodiverse stands were subject to self-thinning and a local boundary line. A feedback loop was observed where biodiversity promoted efficient space occupations but, as these approached their maximum, fierce competition for space eliminated the weaker species. In the background, water availability mediated the strength of this interaction. Our results fit the ‘intermediate disturbance hypothesis’ and can unify seemingly contradicting past evidence and theories. 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 grasslands in Africa and elsewhere resulted from the accumulation of dead plant biomass occupying space otherwise available for the growth of new plants.