Old British grasslands might die hard in the face of climate change

Abstract

Community stability has long attracted the attention of ecologists, who normally consider two components. One is resistance, the ability of a community to maintain its composition and biomass in response to environmental change. The other is resilience, or the rate of recovery. Until recently, this remained largely a theoretical issue. However, the projected global changes in climate and land use have brought resistance and resilience into the limelight of empirical ecology. Several characteristics of plant communities have been proposed as key determinants of their resistance and resilience in the face of global change. Four of these characteristics feature prominently in the literature: the previous exposure of the community to the changing environmental factor in question, the species richness of the community, its successional status and the traits of the component species.J.P. Grime et al.1xThe response of two contrasting limestone grasslands to simulated climate change. Grime, J.P. et al. Science. 2000; 29: 762–765Crossref | Scopus (197)See all References1 add a solid contribution to the debate, comparing the resistance of different herbaceous communities in the face of climate change. They summarize the effects of five years of climatic manipulations on limestone grasslands. The treatments consisted of simulating increased winter temperature, summer drought and increased rainfall. They were applied to two calcareous grasslands with similar diversity, but differing strongly in terms of history of climate, successional age and traits of the dominant species. The impacts of climatic manipulations on both whole-community biomass and species composition were stronger in the fertile old-field community of Southern England, despite its flora showing similar diversity and being more accustomed to dry and warm conditions than the old pasture of Northern England. According to the authors, the explanation lies in the traits of the dominant species and the successional status of the grasslands. The Northern grassland is an infertile late-successional community, dominated by slow-growing perennial graminoids, whereas the Southern grassland is a fertile early-successional community dominated by fast-growing, short-lived plants. The theoretical implications are relevant to current discussions in ecology. Past climatic experience and species richness might not be enough to predict resistance, and the traits of the members of the community seem to play a determinant role. The practical implications are also important: traditionally managed old pastures are expected to respond more slowly than more ‘modern’ landscapes, and therefore to be at less risk in the face of climatic change. Those involved in conservation should not jump to conclusions too quickly, the authors warn, because there is another side to the coin. Previous work suggests that resistance is negatively correlated with resilience. These grasslands might die hard, but when pushed beyond their resistance threshold they might recover very slowly or not at all. Also, current land-use practices are quickly transforming old-traditional landscapes into weedy, faster-changing systems, which, in turn, are more vulnerable to climate change.This is a fine example of how much theoretical and practical insight can be gained from a broad perspective combined with strong empirical results. Time-consuming, old-fashioned, long-term field experiments might be difficult to fund but once again they have proved extremely valuable.