Rein Kalamees

THE ROLE OF THE SEED BANK IN GAP REGENERATION IN A CALCAREOUS GRASSLAND COMMUNITY

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 X 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 flow- erheads in 2 X 2 m plots, and the prevention of lateral clonal spread by surrounding gap soil with 41-pum 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/ m2 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 ( 0.5 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 seed- lings, 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.

Restoration of species-rich limestone grassland communities from overgrown land: the importance of propagule availability

A field experiment was established in the eastern coast of the Baltic Sea to test the relative roles of the availability of propagules and light competition in the restoration dynamics of a former calcareous grassland overgrown by pine (Pinus sylvestris L.). The treatments were: clear-cutting of trees with additional grazing and transplantation of sods from an open grassland with all possible sources of propagules. Species richness and composition were studied on a small-scale during 7 years in the transplanted patches of 20×20 cm and in their surroundings of 50×50 cm. In the cut and grazed site the species richness increased. Transplantation of sods from an open species-rich grassland did not result in higher richness even in their closest surroundings. In the forest, transplanted patches lost their high species richness by the second year. In the cut and grazed site, transplanted patches remained species-rich, but after 3 years, control patches reached the same level of species richness. In landscapes where former species-rich limestone grasslands are overgrown, but the local species pool has not yet changed, restoration of semi-natural grassland communities does not require the additional input of diaspores of grassland species. Transplantation of sods is potentially important method of community restoration in case of impoverished local species pools.

Alvar grasslands in Estonia: variation in species composition and community structure

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 releves, 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 Oland, 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.

Soil seed bank composition in different successional stages of a species rich wooded meadow in Laelatu, western Estonia

Abstract We studied the seed bank of a calcareous grassland in four sites with different management history: original old grassland, which has been described as one of the richest plant communities in Europe, long-term restored grassland, which has been overgrown in the seventies, recently overgrown (ca. 20 years ago) and long-term overgrown grasslands. The seed banks in grassland sites at Laelatu were small both in size and number of species. The number of species and seeds in the seed bank declined significantly from managed grasslands to closed overgrown community. The highest species richness of the soil seed bank (number of species per soil volume) was found in the managed grassland sites, the seed density in the bank was the highest in the long-term restored grassland site. About one third of all the grassland species were found in the seed bank. The proportion of species in the established vegetation — represented also in the bank — was higher in overgrown sites. However, ordination (Correspondence Analysis), which also took into account species frequencies, showed that the similarity between established vegetation on plots and seed bank samples decreased from original grassland to closed overgrown grassland. The persistence of the seeds of only 8–10 typical grassland species in the seed bank of overgrown grassland sites makes the significance of the seed bank for community restoration quite small.

The seed bank in an estonian calcareous grassland: Comparison of different successional stages

Seed bank species-composition and seed-density were determined in a successional calcareous (alvar) grassland in western Estonia. Three similar study areas were chosen to compare two different successional stages: open alvar grassland and overgrown areas with young pine forest 30 to 40 years old. In both successional stages, the centre and the edge of a relatively uniform stand were examined. Fifteen soil samples (7 cm in diameter, 5 cm deep) were taken from each of twelve sampling sites. The seedling emergence method was used to estimate seeds in the soil samples.A total of 69 species were detected in the seed bank, of which 18 did not occur in the vegetation. Eighty-nine taxa were recorded in the vegetation and of these 38 were not detected in the seed bank. Fifty-one species occurred both in the seed bank and in the vegetation. The three most abundant taxa in the seed bank wereCarex tomentosa, Linum catharticum andPlantago media, which together made up 49% of the seedlings recorded.Differences in the species compositions of seed bank samples from grassland and forest sites were negligible, although the species richness per area of the above-ground vegetation was significantly higher in the open grassland. The only species tending to be lost from forest site vegetation but still occurring in the forest soil seed bank wereArenaria serpylifolia, Cerastium fontanum andLinum catharticum. About half of all the emerged species from all samples belonged to the transient or short-term persistent seed bank. In the grassland sites there were more species which belonged to the transient seed bank than in the forest sites, where the seed bank contained more short-term persistent type seeds. The seed density was significantly higher in forest sites and lower in grassland sites, which may be explained by the better germination conditions in well-illuminated communities. On the basis of the current study it might be assumed that the soil seed banks of overgrown alvar grasslands which include young pine forests can play a certain role in grassland restoration management.

Diversity and dispersal - can the link be approached experimentally?

It has been hypothesized that the relative role of species dispersal in determining plant community composition and species richness changes along primary productivity and disturbance intensity gradients. Manipulative experiments with either diaspore addition or prevention are needed to validate this hypothesis. Due to methodological constraints, diaspore prevention experiments are rarely used. In the case of diaspore addition experiments, there are some potential sources of error. (1) Experiments may be confounded since patchiness of microbial communities is not considered and techniques equalizing microbial communities over study plots are not used. (2) The length of the period of observation may not be sufficient to understand whether the establishment of sown individuals was really successful. (3) The effect of the sowing treatment and the theoretical context of the whole experiment depends on the number and identity of species sown. When addressing the role of long-distance dispersal, it is almost impossible to say what the appropriate number and composition of species to be used for the experiment should be. (4) Until now, most of the attention has been on dispersal in space, while the role of “dispersal in time” (seed bank) has rarely been addressed. We conclude that stepwise accumulation of experimental studies, addressing the role of dispersal in shaping plant communities, will sooner or later reveal general patterns, given the experiments are well planned and aim to avoid the sources of errors described above.

Past and present effectiveness of protected areas for conservation of naturally and anthropogenically rare plant species.

The Global Strategy of Plant Conservation states that at least 60% of threatened plant species should be within protected areas. This goal has been met in some regions with long traditions of plant protection. We used gap analysis to explore how particular groups of species of conservation interest, representing different types of natural or anthropogenic rarity, have been covered by protected areas on a national scale in Estonia during the last 100 years. Species-accumulation curves indicated that plant species that are naturally rare (restricted global or local distribution, always small populations, or very rare habitat requirements) needed almost twice as many protected areas to reach the 60% target as plant species that are rare owing to lack of suitable management (species depending on grassland management, moderate forest disturbances, extensive traditional agriculture, or species potentially threatened by collecting). Temporal analysis of the establishment of protected areas suggested that grouping plant species according to the predominant cause of rarity accurately reflected the history of conservation decision making. Species found in very rare habitats have previously received special conservation attention; species dependent on traditional extensive agriculture have been largely ignored until recently. Legislative initiative and new nature-protection schemes (e.g., Natura 2000, network of protected areas in the European Union) have had a positive influence on all species groups. Consequently, the species groups needing similar action for their conservation are sensitive indicators of the effectiveness of protected-area networks. Different species groups, however, may not be uniformly conserved within protected areas, and all species groups should fulfill the target of 60% coverage within protected areas.

Threatened herbaceous species dependent on moderate forest disturbances: A neglected target for ecosystem-based silviculture

Abstract Biodiversity conservation should be considered in forest management. Most forests have a long history of moderate human disturbances. In the temperate region this coevolution has resulted in high species diversity since many threatened herbaceous species depend on moderate forest disturbances. This study considered these species in Estonia. One-third of Estonian threatened herbaceous species were estimated to be dependent on moderate forest disturbances. All of these species are favoured by small-scale gaps through partial cutting or allowing natural uprooting of trees to occur. Several species are favoured by moderate soil disturbances (paths, horseriding, etc.) and clearing of undergrowth. A smaller number of species are favoured by grazing or by prescribed fires. Disturbance-dependent species ranked high in the national Red Data Book and they were particularly characteristic in dry forests. Disturbance-dependent herbaceous species should be considered as a target group for ecosystem-based forest management. Moderate disturbances are required in both managed and protected forests to conserve forest biodiversity.

Intra-individual ITS polymorphism and hybridization in Pulmonaria obscura Dumort. and Pulmonaria angustifolia L. (Boraginaceae)

Internal transcribed spacer (ITS) is used as a molecular marker in most phylogenetical analyses in Boraginaceae, an unplaced group in the current angiosperm phylogeny. However, there is no knowledge on intra-individual polymorphism of ITS in Boraginaceae. Difficulties in PCR and sequencing of ITS in Pulmonaria species mentioned in the literature may be seen as indirect evidence of intra-individual polymorphism. This study aims to detect intra-individual polymorphism of ITS1–5.8S–ITS2 in rare species Pulmonariaangustifolia L. and common species Pulmonariaobscura Dumort. Cloning of ITS sequences of P. angustifolia, P. obscura and putative hybrid specimens from mixed population showed intra-individual polymorphism of ITS1–5.8S–ITS2 in all specimens, whereas most of them also contained pseudogenic sequences. Intra-individual sequence divergence of ITS1 and ITS2 spacers was similar in the P. angustifolia and mixed population and significantly higher than in P. obscura. P. angustifolia specimens had nucleotide polymorphisms characteristic to both P. angustifolia and P. obscura and part of P. angustifolia sequences clustered into mostly P. obscura clade on the neighbour-joining trees based on ITS1 sequence and ITS2 sequence and structure data. These results suggest a hybrid origin of all P. angustifolia populations studied. Thus, outbreeding depression is a likely explanation for the decline in populations near the northern border of distribution area of rare species P. angustifolia. Hybrid origin of the whole P. angustifolia is also probable; the central population from Poland showed a similar pattern of polymorphism as distribution edge populations.

Microbial island biogeography: isolation shapes the life history characteristics but not diversity of root-symbiotic fungal communities

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.