Impacts of Biodiversity Loss Escalate Through Time as Redundancy Fades

Experimental ecological studies in recent years have provided a great deal of insight into how species diversify and influence ecosystem properties, but in most cases the experiments have been relatively brief (up to ∼5 years). Reich et al. (p. 589; see the Perspective by Cardinale) performed two 13- and 15-year grassland experiments and found that the effects of plant species richness on community-level processes like biomass production tend to be saturating at early stages but that those impacts grow stronger and more linear as experiments run longer. Stronger influences through time were largely driven by increasing amounts of “complementarity” among species, and these trends were correlated with greater expression of functional diversity in multispecies assemblages. Thus, the effects of diversity grow stronger through time as species gain more and more opportunity to vary in their use of the limiting biological resources in their environment, which emphasizes the functional importance of maintaining diversity in ecosystems.

Plant diversity generally promotes biomass production, but how the shape of the response curve changes with time remains unclear. This is a critical knowledge gap because the shape of this relationship indicates the extent to which loss of the first few species will influence biomass production. Using two long-term (≥13 years) biodiversity experiments, we show that the effects of diversity on biomass productivity increased and became less saturating over time. Our analyses suggest that effects of diversity-dependent ecosystem feedbacks and interspecific complementarity accumulate over time, causing high-diversity species combinations that appeared functionally redundant during early years to become more functionally unique through time. Consequently, simplification of diverse ecosystems will likely have greater negative impacts on ecosystem functioning than has been suggested by short-term experiments.