ABSTRACT
The mass-ratio effect is used as a proxy of the selection effect and can be tested by determining whether variation in ecosystem functioning is related to the community-weighted mean of species traits. The majority of biodiversity and ecosystem functioning (BEF) studies of forest systems have reported positive relationships between species richness and forest productivity at regional and continental scales, although negative and non-significant BEF relationships have also been reported. The mass ratio hypothesis predicts that ecosystem properties should be largely determined by the characteristics of the dominant species within a community. Mass ratio effects are likely observed to dominate in fertile regions, and functional diversity may play a larger role in determining ecosystem functions in harsher environments. The strong positive effects of stand age on biomass were attributed to cumulative tree growth over time. Stand age may also directly affect biomass and productivity via changing stand structure and/or species diversity as forests develop.
