JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology. Abstract.To evaluate the relative roles of seed availability and competitive interactions in creating within-community patterns of species richness in unproductive grassland, we conducted a sowing experiment in a dry calcareous (alvar) grassland, where both the number of arriving seeds and the number of arriving species were approximately doubled compared to the natural seed rain. Also, in half of the plots, 36% of the vegetation and bryophyte cover was removed to simulate disturbance. Sowing significantly increased species richness and the number of seedlings in plots. Disturbance increased the number of seedlings but had no significant effect on species richness. In the first year, the highest number of seedlings was found in disturbed and sown plots. The dynamics of seedling numbers differed among species. Of the 15 sown species, seedlings of nine species were found in some plots. The number of seedlings of two species were not dependent on treatments, those of three species depended only on sowing, and for four species there was a significant positive interaction between sowing and disturbance. The establishment of sown species was not dependent on initial species richness or number of adult ramets in experimental plots. It was concluded that, though the behavior of individual species may differ, the local deficiency of seeds may be an important force generating small-scale community patterns of calcareous grasslands.

To evaluate the relative roles of seed availability and competitive interactions in creating within-community patterns of species richness in unproductive grassland, we conducted a sowing experiment in a dry calcareous (alvar) grassland, where both the number of arriving seeds and the number of arriving species were approximately doubled compared to the natural seed rain. Also, in half of the plots, 36% of the vegetation and bryophyte cover was removed to simulate disturbance. Sowing significantly increased species richness and the number of seedlings in plots. Disturbance increased the number of seedlings but had no significant effect on species richness. In the first year, the highest number of seedlings was found in disturbed and sown plots. The dynamics of seedling numbers differed among species. Of the 15 sown species, seedlings of nine species were found in some plots. The number of seedlings of two species were not dependent on treatments, those of three species depended only on sowing, and for four species there was a significant positive interaction between sowing and disturbance. The establishment of sown species was not dependent on initial species richness or number of adult ramets in experimental plots. It was concluded that, though the behavior of individual species may differ, the local deficiency of seeds may be an important force generating small-scale community patterns of calcareous grasslands.

No abstract

Large-scale changes in regional floras provide direct information about changes in biodiversity through time and enable the evaluation of conservation targets. We compared the distribution ranges in 2004 of Estonian native terrestrial flora with the distribution ranges before 1970, using the Atlas of Estonian Flora. Relative persistence was related to species endemism, commonness, occurrence at its border of the global distribution range, main habitat type, sensitivity to human impact, life-form, conservation category, and Red List category. A literature-based database of the flora of Estonian habitat types was used to evaluate relative persistence of the flora of different habitats. Changes in the flora are largely dependent on human activities. The decrease in mire and grassland habitats and the increase in forests are reflected in the persistences of related species. Flora of mire habitats decreased the most. The fact that an almost ten-fold decrease of grasslands has not resulted in as large a decrease in the ranges of grassland species could serve as evidence of the extinction debt of these habitats. We also found a greater decrease among habitat specialists than habitat generalists and lower average persistence of the species of species-rich habitats. Our data show that current prioritization of species for conservation is in concordance with needs, as reflected in the changes in the range of species. However, conservation has not been entirely successful: the decrease of protected species continues. Our simple method for summarizing large databases was effective for the evaluation of large scale effects of conservation actions.

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.