Small‐scale turnover in a calcareous grassland, its pattern and components

Abstract

Abstract. We studied small‐scale turnover in a calcareous grassland community in 2 cm × 2 cm subplots within 46 10 cm × 10 cm plots from 1996 to 1999. In different years, 73–84% of the subplots were occupied by rooted plant individuals, but the location of empty subplots varied considerably between years. Seedlings were the most mobile components in subplots – during one year (from July to July), seedlings either appeared or disappeared in on average 85% of all subplots where seedlings had occurred during that year. Within a one‐year period, vegetative ramets appeared or disappeared in an average of 30% of all subplots that had rooted plants at either the beginning or the end of that year. When only previously empty subplots were taken into account, 80% of appearances were due to clonal growth and 20% due to seedling establishment. Ca. 75% of the seedlings, however, established in subplots that already contained a rooted plant individual. There were significantly less generative appearances when a moist summer was followed by a dry one, and significantly more vegetative appearances when a dry summer was followed by a moist one. 24–33% of the established seedlings survived the first year; from the second year onwards the annual survival was greater than 50%. Seedling survival was higher among shortlived species. Generative turnover varied between species, but we found no correlation with life history characteristics or frequency. Vegetative turnover of species was dependent on the year and on species traits. Sedges had a significantly higher turnover than grasses. Species potentially able to move clonally > 10 cm per year had a higher turnover than slower species. Turnover was not dependent on species frequency in the community. Forbs with more seedlings also had a higher vegetative turnover. There were no evident links between spatial mobility and species coexistence; predominating species exhibited contrasting turnover rates, subordinate species had contrasting turnover rates as well. Turnover is important in more general terms as a process resulting in free gaps – arenas for recruitment of whatever species.