Patterns of species richness in a limestone grassland under different treatments in relation to spatial scale

. In an experiment in a limestone grassland on the Baltic island of Oland, SE Sweden, nutrient and water supply, light intensity and grazing regime were altered in 10 combinations during four years in 10 plots of 0.25 m2 with subplots of 0.01 m2 and 0.0004 m2. Only the combined application of fertilizer and shade led to a strong decrease in average species richness (S1) at all scales. When comparing species numbers summed up over all 10 replicates of each treatment (Sn) at the three quadrat sizes, differences in effect of these treatments were much smaller, and were so already at the finest scale. a-diversity, measured as (Sn - S1 was quite constant over different scales for most treatments, i.e. diversity did not increase with an increase in scale. The richness ratioSn/S1 decreased with increasing scale, indicating an increasing degree of homogeneity at larger scales. Treatments which only included fertilizer or shade, maintained high species richness; this high richness was also maintained in combination with grazing and could then be explained by the denser packing of vegetation. Patterns of species richness were correlated at the large scale, but not at the finer scales, indicating a high degree of spatial and temporal heterogeneity at the finer scales. With increasing quadrat size species persistence increased which explains the small effect of certain treatments. Clearly, a range of scales has to be sampled in this type of vegetation to be able to measure different patterns, which may occur under different experimental treatments. The finest scale in this study can become too small, when certain treatments result in a coarse-grained vegetation pattern. The quadrat size of 10 cm x 10 cm should be included in the range of scales. It combines accuracy in sampling with efficiency in time effort, a reasonably large number of species sampled, and a strong differentiation in the effects of the various treatments.