Summary 1.We investigated the vertical distribution of seeds in the soil, using data from nine studies in five European countries. We discovered significant correlations between seed shape and distribution in the soil. 2. The classification of the longevity of seeds of plant species has been improved by the introduction of a 'longevity index', expressing on a continuous scale the most recent information on seed longevity represented as the proportion of non-transient seed bank records in the database of Thompson et al. (1997). Remarkably, no difference in seed longevity was found if the index was based on direct observations only when compared with the index based on the complete data set where indirect, 'depthderived' observations were included. 3. Seed longevity was best estimated using a multiple regression model with an integrated measure of seed size and shape and depth distribution of seeds. 4. The shape of seeds, known to be a consistent character of species, was shown to be constant within species, whereas depth distribution of seeds was highly variable among sites. This is consistent with the variability of seed longevity found in published seed bank data.

We conducted a factorial field experiment in order to investigate the role of the soil seed bank in gap recolonization in a calcareous grassland, using 240 experimental gaps (10 ϫ 10 cm). Experimental manipulations included the elimination of the seed bank (by sterilizing the soil), the elimination of short-distance seed rain by removing all flowerheads in 2 ϫ 2 m plots, and the prevention of lateral clonal spread by surrounding gap soil with 41-m nylon mesh. The influence of competition on regeneration was also studied, by planting an adult individual of Filipendula vulgaris or Festuca rubra in the center of some gaps.There were 130 species of vascular plants in the established vegetation. Twenty-five species also occurred as seedlings; 51 species were recorded in the seed bank, of which only two were not present in the growing vegetation. There were on average 2362 seeds/ m 2 in a 10 cm deep soil layer. Species relative abundances in the established vegetation and in the seed bank were not significantly correlated.Eighty-four vascular plant species emerged from seeds in the experimental gaps. The seed bank contributed on average 5.4 seedlings per gap, short-distance seed rain (Ͻ0.5 m) 4.1 seedlings, and longer distance (Ͼ0.5 m) seed rain 2.7 seedlings. Thirty-one vascular plant species arrived in experimental gaps by lateral clonal spread. Of these, only one was not recorded as a seedling in the experimental gaps. There were on average 2.7 clonally spread shoots per gap. Species with smaller seeds were present in significantly greater numbers in the seed bank than in the vegetation and were also more common colonizers of experimental gaps. There was no evidence of competition or facilitation between seedlings, or between seedlings and adults.It was concluded that the soil seed bank has an important functional role in a perennial grassland community as a means for population maintenance for many species. Thirty-six percent of the regeneration in small gaps was due to the seed bank, and one may expect that this proportion will increase in larger gaps.

Abstract. In order to understand the variation of Estonian calcareous thin‐soil grasslands on Ordovician or Silurian limestone (alvars), 58 stands, distributed over the whole alvar region of Estonia, were described and clustered numerically using TABORD. Alvars are characterized by a high species richness. These mainly semi‐natural communities have mostly developed after clear‐cutting of forests. Grazing by domestic animals and removal of woody plants is needed for their maintenance. Primary (natural) alvar grasslands are found in a few places in coastal regions or in areas with thin‐soil on monolithic bedrock. In data processing a whole stand, described by several small relevés, was used in the classification as one description, including species frequencies as a quantitative measure. Seven clusters were separated and their configuration checked in a PCA‐ordination. The resulting classification agreed with the previous ‘rough’ classification. Both geographical and ecological factors were related with the clustering and the ordination. The broad classification units, suggested for Estonian alvar grasslands, were quite similar to the ones described earlier for alvar vegetation on Öland, Sweden. Clusters differed in their species richness, environmental conditions and life‐form spectra. Differences in species richness were defined by regional species pools. Compared to earlier surveys, only a small fraction of alvars still remains in Estonia. Active conservation, i.e. suitable management is needed to protect the still surviving valuable plant communities. The present study can provide guidelines on how to protect and manage different types of alvars in Estonia.

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Island biogeography theory is one of the most influential paradigms in ecology. That island characteristics, including remoteness, can profoundly modulate biological diversity has been borne out by studies of animals and plants. By contrast, the processes influencing microbial diversity in island systems remain largely undetermined. We sequenced arbuscular mycorrhizal (AM) fungal DNA from plant roots collected on 13 islands worldwide and compared AM fungal diversity on islands with existing data from mainland sites. AM fungal communities on islands (even those >6000 km from the closest mainland) comprised few endemic taxa and were as diverse as mainland communities. Thus, in contrast to patterns recorded among macro-organisms, efficient dispersal appears to outweigh the effects of taxogenesis and extinction in regulating AM fungal diversity on islands. Nonetheless, AM fungal communities on more distant islands comprised a higher proportion of previously cultured and large-spored taxa, indicating that dispersal may be human-mediated or require tolerance of significant environmental stress, such as exposure to sunlight or high salinity. The processes driving large-scale patterns of microbial diversity are a key consideration for attempts to conserve and restore functioning ecosystems in this era of rapid global change.