Density and assemblage influence the nature of the species richness–productivity relationship in Australian dry sclerophyll forest species
Mallett, RK and Hovenden, MJ, Density and assemblage influence the nature of the species richness-productivity relationship in Australian dry sclerophyll forest species, Austral Ecology, 40, (2) pp. 109-116. ISSN 1442-9985 (2015) [Refereed Article]
The relationship between species richness and productivity is important from both a basic, theoretical perspective and also because it has important ramifications for applied ecology including ecosystem restoration and the design of carbon offset plantings. While a more species-rich community is often believed to be more productive than a species-poor community, findings from observational and experimental studies differ and our understanding of the relationship comes largely from grasslands. Consequently, we aimed to determine for the first time the nature of the species richness–productivity relationship in a southern-hemisphere dry sclerophyll ecosystem. We investigated the impact of species richness on productivity, plant density and mean plant biomass at three sowing densities in three species assemblages. Eucalyptus globulus, Acacia mearnsii and Allocasuarina verticillata were each grown as monocultures and included in every subsequent level of species richness, forming three distinct species assemblages. Communities were grown in a glasshouse pot experiment for four months, then harvested and above-ground biomass measured. We found no general species richness–productivity relationship in the communities studied. There were no overall increases in productivity as species richness increased and in fact in most cases the productivity of communities with 4 and 8 species was lower than monocultures of the dominants. Importantly, density influenced the way richness affected productivity and this effect was dependent upon assemblage, indicating that species identity is a key determinant of productivity. These results demonstrate important ecological principles in a previously untested system. A key outcome of this experiment is that density alters the relationship between species richness and initial productivity in assemblages of Australian dry sclerophyll species.
species richness, productivity, community assembly, community ecology, sclerophyll forest, ecosystem function, diversity-productivity relationship