Rio + 20 in Nature

In the run up to the Rio+20 conference, the June 6 issue of Nature put together a fascinating set of articles assessing the current state of knowledge on the two issues that dominated the original Rio agenda: biodiversity and climate change.



1) In "Biodiversity and its Impact on Humanity" Cardinale et.al. review current understanding about the role of biodiversity in relation to ecosystem functioning and the provision of ecosystem services. Key findings re: ecosystem functioning:

• There is now unequivocal evidence that biodiversity loss reduces the efficiency by which ecological communities capture biologically essential resources, produce biomass, decompose and recycle biologically essential nutrients.
• There is mounting evidence that biodiversity increases the stability of ecosystem functions through time.
• The impact of biodiversity on any single ecosystem process is nonlinear and saturating, such that change accelerates as biodiversity loss increases.
• Diverse communities are more productive because they contain key species that have a large influence on productivity, and differences in functional traits among organisms increase total resource capture.
• Loss of diversity across trophic levels has the potential to influence ecosystem functions even more strongly than diversity loss within trophic levels.
• Functional traits of organisms have large impacts on the magnitude of ecosystem functions, which give rise to a wide range of plausible impacts of extinction on ecosystem function.
• The impacts of diversity loss on ecological processes might be sufficiently large to rival the impacts of many other global drivers of environmental change.
• Diversity effects grow stronger with time, and may increase at larger spatial scales.
• Maintaining multiple ecosystem processes at multiple places and times requires higher levels of biodiversity than does a single process at a single place and time.
• The ecological consequences of biodiversity loss can be predicted from evolutionary history.

The findings re: ecosystem services were more tentative:

• There is now sufficient evidence that biodiversity per se either directly influences (experimental evidence) or is strongly correlated with (observational evidence) certain provisioning and regulating services.... For provisioning services, data show that (1) intraspecific genetic diversity increases the yield of commercial crops; (2) tree species diversity enhances production of wood in plantations;
  (3) plant species diversity in grasslands enhances the production of fodder; and (4) increasing diversity of fish is associated with greater stability of fisheries yields. For regulating processes and services, (1) increasing plant biodiversity increases resistance to invasion by exotic plants; (2) plant pathogens, such as fungal and viral infections, are less prevalent in more diverse plant communities; (3) plant species diversity increases above ground carbon sequestration through enhanced biomass
  production (but see statement 2 concerning long-term carbon storage); and (4) nutrient mineralization and soil organic matter increase with plant richness.
• For many of the ecosystem services reviewed, the evidence for effects of biodiversity is mixed, and the contribution of biodiversity per se to the service is less well defined.
• For many services, there are insufficient data to evaluate the relationship between biodiversity and the service.
• For a small number of ecosystem services, current evidence for the impact of biodiversity runs counter to expectations.

2) In "A global synthesis reveals biodiversity loss as a major driver of ecosystem change" Hooper, et. al. summarize evidence showing that extinctions are altering key processes important to the productivity and sustainability of Earth’s ecosystems

3) In "Approaching a state shift in Earth’s biosphere" Barnosky et. al. review the basics of state shift theory, review the evidence relating to past planetary-scale critical transitions and state shifts, and examine research related to a number of contemporary global-scale forcing mechanisms: human population growth with attendant resource consumption, habitat transformation and fragmentation, energy production and consumption, and climate change.

4) The political/policy pieces -- documenting how poorly nations have done in realizing their 1992 promises and describing developments that hold out the potential for a more optimistic future -- are worth checking out as well, but they are significantly less interesting than the articles summarizing current scientific knowledge.