A test of the humped-back theory of species richness in New Zealand native forest

The Humped-back theory of plant species richness, a theory related to Grime's C-S-R 'triangular' model, has been widely discussed, and some evidence has been claimed in support of it. The theory suggests that species richness is maximal at intermediate levels of productivity, i.e., at intermediate positions on a stress/favourability gradient. We sought evidence for the theory from 90 stands of native podocarp/broadleaved and beech forest in the Coastal Otago region, with an adjustment made for the effect of stand area on species richness. There was no relation between adjusted species richness and an index of site stress/favourability, i.e., no support for the Humped-back theory. The theory may be inapplicable to woody vegetation, or it may be applicable only when the 'favourable' end of the spectrum comprises agricultural communities, or support for the theory might be inflated in the literature by a wish to find ecological generalisations.