Effects of ozone on calcareous grassland communities

A system of 16 open-top chambers was used to investigate the effects of a range of ozone concentrations typical of those found in southern Britain on the species composition of calcareous grassland communities. Two experimental approaches were adopted: the first involved the use of artificial communities of species typical of calcareous grasslands, whilst the second involved semi-natural chalk grassland swards transplanted from the field. Elevated ozone had little effect on total biomass of the artificial communities, but did significantly alter the species composition. The proportion of forbs decreased linearly with increased ozone exposure above 40ppb. Species composition was stable in the transplanted swards receiving filtered air, whilst there was a shift towards what appeared to be a more calcareous grassland community in the swards treated with higher ozone exposures. Thus, both experiments provide evidence that ambient levels of ozone in southern Britain can cause changes in species composition of semi-natural calcareous grassland communities.