Functional diversity indices reveal the impacts of land use intensification on plant community assembly

1. Functional diversity has been suggested as an important descriptor of an assemblage and as an indicator of ecosystem function. However, there has been little testing of recent functional diversity measures on field data and across environmental gradients of disturbance and productivity. This study tested how three recently developed measures of functional diversity behave in practice and what could be deduced about assembly rules operating in the systems studied. 2. Data from 30 plant communities in a small area, comprising arable fields, mown and grazed grasslands, moorland and woodland, were analysed in terms of these diversity indices. Functional Divergence, Evenness and Richness were independent of each other, but Richness correlated to species diversity through the sampling effect. 3. As evidenced by reduced Functional Richness, habitat filtering operated at a significant proportion of the sites sampled. Functional Richness was also reduced against expectations at high levels of both productivity and disturbance. Functional Divergence showed no clear patterns, but Functional Evenness showed a clear promotion by disturbance and a reduction at high standing biomass. 4. Synthesis. Knowledge of how functional diversity is related to the environment provides indications of the processes governing community assembly, and the possibility of developing them as measures of ecosystem function.