HIGH SPECIES MOBILITY IN SPECIES-RICH PLANT-COMMUNITIES - AN INTERCONTINENTAL COMPARISON

Using results from a long-term study of fine-scale dynamics in grassla nds in four widely separated study areas from two continents, we provi de further evidence to support the idea of the carousel model as an ai d to describe the high fine-scale temporal and spatial species mobilit y found in grassland communities. Cumulative species numbers on small subplots in plots situated in stable plant communities, determined as the sum of species appearing in these subplots in one or more years ov er a period of time, are very high. In floristically different species -rich grasslands, varying from moist pine savannas in North Carolina a nd Mississippi, to humid chalk grassland in the Netherlands and season ally dry limestone grassland in Sweden, average species numbers on sub plots of 0.01 m2 in plots of 2.5 m2 over the period 1985-1989 were sim ilar, most plots falling in the range 10.8 - 13.2. The total cumulativ e species numbers were similar as well, most plots falling in the rang e 17.4 and 20.9. Yearly average species numbers remained relatively co nstant. Considerable species turnover is occurring in all these commun ities; on average three species appear and three disappear each year i n each 0.01 m2 subplot. Total species accumulation on 0.01 m2 subplots over the period 1985-1989 varied considerably, from 4.1 to 11.6, and is correlated with the cumulative species total on the plot, the latte r figure being considered as correlated with the size of the species p ool.