Unwinding the indirect effects of climate change on ecological communities

Background/Question/Methods

Interactions between species can generate unforeseen complexities in the ways that communities respond to a change in climate. These “indirect effects” of climate change challenge efforts at predicting and managing ecological futures.  It is possible that if we can identify key indirect effects that most strongly govern system dynamics, we may be able to simplify interactions into tractable terms that can improve predictive understanding.  In this study, we assess whether the indirect responses observed in a California grassland community subject to ten years of alternative precipitation regimes can be resolved to the level of a single major driver: nitrogen fixation.  We then implement a nested experiment selectively removing the nitrogen-fixer response from communities and ask whether this reduces the role of indirect relative to direct effects in community responses through five subsequent years of rainfall addition.

Results/Conclusions

We report on the first three years of results, confirming that nitrogen fixation plays a crucial role in driving the indirect responses to rainfall addition observed in this community. We further demonstrate a weakening of major indirect effects in this system and at least a partial reversal of long-term changes in production and diversity as a result of removal of the nitrogen-fixer response.  Our results indicate that the complexities generated by indirect effects may become tractable by the identification and management of their most proximal drivers.