FINE-SCALE SPATIAL POPULATION-PATTERNS AND MOBILITY OF WINTER-ANNUAL HERBS IN A DRY GRASSLAND

Winter annuals were mapped in a series of permanent plots located in g aps in an Austrian dry grassland over a period of 3 yr. Great differen ces in abundance were found among nine winter annuals - Arabis auricul ata, Arenaria leptoclados, Cerastium glutinosum, Erophila spathulata, Holosteum umbellatum, Hornungia petiaca, Saxifraga tridactylites, Thla spi perfoliatum and Veronica praecox - occurring in the gaps. The abso lute frequency of species varied considerably from year to year, while their relative proportions remained nearly constant in the plots over the study period. High spatial dissociation (low level of spatial coi ncidence) between populations was observed; this was ascribed to boleo chory, known to generate monospecific patches. No trend in self-replac ement of a species was found. This means that occupying a place in one year does not necessarily mean the same place will be occupied in fol lowing years. The probability of a species replacing another was found to be low. The space could be inhabited by any species or remain unoc cupied. We suggest that the distribution patterns of species are contr olled by dispersal and preference for microhabitats, at least at the s cale of 20 cm x 20 cm. It was shown by a permutation method based on c umulative frequencies, that at smaller scales the habitat differentiat ion vanishes. We suggest that, up to a typical dispersal range of the winter annuals, the Carousel model can be applied due to the lack of c oincidence (and presumably also interactions) of individuals. Neverthe less, time may eliminate the habitat differentiation at any scale. A d esign of an improved data-sampling and a handling procedure was develo ped.