Increases in plant phenotypic diversity in response to aridity and grazing

Led by Yoann Le Bagousse-Pinguet of Avignon University, an international team of researchers undertook global field surveys of drylands, gathering data on plant morphology, traits and the chemical composition of the 301 plant species encountered. A compilation of more than 130,000 trait measurements revealed that once an aridity threshold has been passed, plant trait diversity in fact doubles.

This threshold represents the transition from semi-arid to arid conditions, and previous studies have shown that once this threshold has been passed, abrupt changes occur, including declines in soil fertility, plant productivity, cover and species richness. The surprising increase in plant functional diversity uncovered in this study was found to be coupled with declines in plant cover, leading the authors of this study to hypothesize that the increase in plant trait diversity was driven by a breakdown in plant–plant interactions that allows unique species to escape competition. This idea was supported by the finding that increases in grazing pressure, a major driver of decreasing plant cover, expand the plant trait space and modulate the aridity threshold at which trait diversity increased.