Will global change improve grazing quality of grasslands? A call for a deeper understanding of the effects of shifts from C 4 to C 3 grasses for large herbivores

The current dramatic increase in atmospheric CO 2 concentration favours C 3 versus C 4 photosynthesis, and although other aspects of environmental conditions come into play, it implies an uncertain future for C 4 grasses. If it has been suggested that the poor quality of C 4 grasses contributed to large mammalian herbivores declines as C 4 grasslands spread from the late Miocene, these investigations of the past have not been matched by a similar attention focused on the future implications of C 4 to C 3 shifts. Here we discuss how these may affect grazing systems, also considering other aspects of C 3 /C 4 differences (productivity, phenology) which might affect herbivore performance. Current knowledge suggests that important changes in herbivore performance could be observed, but is too fragmentary to allow general quantitative conclusions. We urge plant and herbivore ecologists to collectively address these limitations, as the future of grazing systems has important implications for biodiversity and human livelihoods.