Climatic fluctuation causes large-scale synchronous variation in radial root increments of perennial forbs

Although there is clear evidence that climate change influences ecological patterns and processes, scientists do not agree on the importance of climate in causing ecological change. Part of the problem is finding large-scale ecological response patterns that are unbiased and unconfounded estimators of the effects of climate change. Here we present evidence that the 1997/1998 El Nino event, associated in 1998 with the highest global surface temperature since 1860, caused synchronous variation in radial increment growth of the main roots of perennial forb species in the United States and in Switzerland. Our a posteriori analysis of annual ring width fluctuations indicates that growth of herbaceous plants responds rapidly and sensitively to climatic fluctuation, while the direction and strength of the response depends on interactions with local conditions. We suggest that analysis of growth rings in the roots of forbs provides a widely applicable approach to detecting effects of both strong global climate variation and regionally limited extreme climatic events on herbaceous vegetation. This new technique of herb-chronology thus helps ecologists to evaluate how competitive balance between plant species in herbaceous vegetation might respond to climate change, with consequences for ecosystem function and diversity.