Data from: When can we expect negative effects of plant diversity on community biomass?

Although experiments overwhelmingly show biodiversity increases ecosystem
functioning, relationships in natural communities are more variable. This
raises the question of whether and when theory would predict negative
diversity effects. We argue that plant communities containing
more stably coexisting core species should have higher biomass production.
However, variation in numbers of transient species, whose abundances
fluctuate strongly and which cannot stably coexist, may not consistently
affect biomass. Distinguishing changes in core and transient
species richness is critical. For instance, recent attempts to use novel
causal modelling approaches have implied negative effects of biodiversity
on biomass. However, we find these approaches also result in negative
relationships when applied to experiments, where we know there is a
causal, positive effect of diversity. We suggest that transient species
contribute disproportionately to the variation in diversity isolated in
these models. We highlight the need for improved approaches to
analysing data from naturally assembled communities and call for increased
attempts to compare results with experimental systems. Synthesis:
understanding the functional consequences of biodiversity loss is critical
but we need to be clear about what type of diversity change we are
measuring and to focus on the loss of stably coexisting, core species.