Density and assemblage influences on the species richness-productivity relationship in Australian dry sclerophyll species

Ruth Mallett
University of Tasmania

Received the Australian Flora Foundation Young Scientist Award for her poster at EcoTas13, a joint conference between the Ecological Society of Australia and the New Zealand Ecological Society, held at The Aotea Centre, Auckland from 24-29 November 2013.

Ruth Mallett1 and Mark Hovenden1
1University of Tasmania

At any given site, a more species-rich community is thought to be more productive than a species-poor community, although this understanding comes largely from grasslands. We aimed to determine the nature of the species richness-productivity relationship in a southern-hemisphere sclerophyll forest system given its importance from a basic, theoretical perspective
as well as for applied ecology. Using three levels of sowing density and three different species assemblages, the impacts of these variables on productivity, plant density and plant biomass were investigated. In each assemblage a different dominant tree species from local forest was grown as a monoculture and included in every subsequent level of species richness. Communities were grown in a glasshouse pot experiment for four months, harvested and above-ground biomass measured. We found no general species richness-productivity relationship in the early-stage communities studied. There were no overall increases in productivity as species richness increased; in most cases the productivity of communities with 4 and 8 species was lower than monocultures of the dominants. 15 species mixtures were equal to or exceeded the biomass of monocultures, primarily due to the addition of another highly productive species. Density influenced the way richness affected productivity and this effect was dependent upon assemblage, indicating species identity is a key determinant of productivity. These results demonstrate important ecological principles in a novel system, regarding the impact a factor such as density has on the species richness-productivity relationship, suggesting the generally believed relationship between richness and productivity may not exist universally in terrestrial plant ecosystems.

Author: Ruth Mallett is in her first year as a research assistant in the school of Plant Science at the University of Tasmania. Research interests include community ecological processes and the importance of biodiversity in the context of changing climates.