Hidden diversity and productivity patterns in mixed Mediterranean grasslands

Abstract

A detailed study of the variation in productivity across a diversity gradient in an experimental Mediterranean grassland examines the effects of a dominant perennial grass species upon the overall diversity–productivity relationship. The experiment took place at the Greek site of the European‐wide BIODEPTH programme. The experimental design is characterized by the use of a number of communities containing annuals and perennials within the total set of manipulated plots. The main results are: 1) a log‐linear relationship between diversity and productivity exists in Mediterranean grasslands synthesized by annuals only, 2) in mixed communities where multiple growth forms coexist, the performance of a dominant or keystone species may reverse or hide the diversity–productivity pattern of a functional or growth form group of species taken separately, and 3) the introduction of the dominant grass in the low‐diversity mixtures creates an ‘inverted’ sampling effect which can produce as an artefact a constant productivity response across the diversity gradient.