Not all disturbances are created equal: a 200-yr flooding event challenges common biodiversity–stability hypotheses

Background/Question/Methods

Within the next 100 years, rising global temperatures will likely increase the frequency and magnitude of both droughts and extreme precipitation events.  In Europe alone, the economic impact of extreme flooding events could be as high as €23.5 billion annually by 2050.  Simultaneously, human activities are reducing global biodiversity, with current extinction rates at ~1000x what they were before human domination of earth’s ecosystems.  The co-occurrence of these global trends may be of particular concern, as higher biodiversity systems could buffer ecosystems against large perturbations, although support for the so-called biodiversity-stability hypothesis has been varied.  Here we present a comprehensive framework for assessing biodiversity-stability relationships and report on the first demonstration of how biodiversity may buffer against negative impacts of flooding.  We use data from a 200-yr flood event that occurred in June 2013 in a grassland biodiversity experiment (Jena, Germany) to show that the fundamental role of biodiversity during environmental disturbance depends on both stress level and resource availability.  

Results/Conclusions

We found that flooding can have overwhelmingly positive effects on productivity due to increased resource availability and rapid cycling of nutrients following the flood.  Though when flooding is severe, plant growth may slow regardless of diversity, as most species likely stop growing completely.  In all cases, the stability of the system is reduced, but for reasons that reflect opposite trends in overall ecosystem function. Furthermore, when flooding is most severe, sensitive species may be lost, and this may prime the system for reduced ecosystem function in the future.  While summer flooding events may have largely positive or neutral effects on productivity, plant diversity must be maintained at high levels to take advantage of positive flooding effects, and to buffer against future loss.