GrassPlot is a collaborative vegetation-plot database organised by the Eurasian Dry Grassland Group (EDGG) and listed in the Global Index of Vegetation-Plot Databases (GIVD ID EU-00-003). GrassPlot collects plot records (releves) from grasslands and other open habitats of the Palaearctic biogeographic realm. It focuses on precisely delimited plots of eight standard grain sizes (0.0001; 0.001;... 1,000 m(2)) and on nested-plot series with at least four different grain sizes. The usage of GrassPlot is regulated through Bylaws that intend to balance the interests of data contributors and data users. The current version (v. 1.00) contains data for approximately 170,000 plots of different sizes and 2,800 nested-plot series. The key components are richness data and metadata. However, most included datasets also encompass compositional data. About 14,000 plots have near-complete records of terricolous bryophytes and lichens in addition to vascular plants. At present, GrassPlot contains data from 36 countries throughout the Palaearctic, spread across elevational gradients and major grassland types. GrassPlot with its multi-scale and multi-taxon focus complements the larger international vegetationplot databases, such as the European Vegetation Archive (EVA) and the global database " sPlot". Its main aim is to facilitate studies on the scale-and taxon-dependency of biodiversity patterns and drivers along macroecological gradients. GrassPlot is a dynamic database and will expand through new data collection coordinated by the elected Governing Board. We invite researchers with suitable data to join GrassPlot. Researchers with project ideas addressable with GrassPlot data are welcome to submit proposals to the Governing Board.

Temperate calcareous grasslands are characterized by high levels of species richness at small spatial scales. Nevertheless, many species from a habitat‐specific regional species pool may be absent from local communities and represent the ‘dark diversity’ of these sites. Here we investigate dry calcareous grasslands in northern Europe to determine what proportion of the habitat‐specific species pool is realized at small scales (i.e. how the community completeness varies) and which mechanisms may be contributing to the relative sizes of the observed and dark diversity. We test whether the absence of particular species in potentially suitable grassland sites is a consequence of dispersal limitation and/or a low ability to tolerate stress (e.g. drought and grazing).We analysed a total of 1223 vegetation plots (1 × 1 m) from dry calcareous grasslands in Sweden, Estonia and western Russia. The species co‐occurrence approach was used to estimate the dark diversity for each plot. We calculated the maximum dispersal distance for each of the 291 species in our dataset by using simple plant traits (dispersal syndrome, growth form and seed characteristics). Large seed size was used as proxy for small seed number; tall plant height and low S‐strategy type scores were used to characterise low stress‐tolerance.Levels of small‐scale community completeness were relatively low (more species were absent than present) and varied between the grasslands in different geographic areas. Species in the dark diversity were generally characterized by shorter dispersal distances and greater seed weight (fewer seeds) than species in the observed diversity. Species within the dark diversity were generally taller and had a lower tolerance of stressful conditions.We conclude that, even if temperate grasslands have high levels of small‐scale plant diversity, the majority of potentially suitable species in the regional species pool may be absent as a result of dispersal limitation and low stress‐tolerance.

We used an extensive dataset (1220 vegetation plots of 1 m(2)) to study vegetation gradients and fine-scale plant diversity in dry calcareous grasslands (including alvar grasslands) in the Baltic Sea region. The study area covers the entire European distributional range of alvar habitats: Sweden (Oland, Gotland, Gotaland), Estonia (Saaremaa, Hiiumaa, north Estonia, west Estonia), and western Russia (Izhora, lzborsk). Fine-scale plant diversity was characterized by species richness and standardized phylogenetic diversity (comparing the observed mean pairwise phylogenetic distance (MPD) with MPD values from random communities). Ordination techniques (DCA) were used to characterize the main vegetation gradient. Variables describing local environment, climate, the biogeographic composition of the plant communities, and geographic location were related to fine-scale species richness and phylogenetic diversity using variation partitioning techniques and linear mixed models. The main vegetation gradient in the dry calcareous grasslands in the Baltic Sea region had a strong geographic component, was associated with soil depth, species' stress- and disturbance-tolerance and the age of the grassland habitat. Fine-scale phylogenetic diversity and species richness were negatively associated suggesting that these two diversity components are influenced by different sets of environmental and historical parameters. Fine-scale species richness was unimodally associated with the main vegetation gradient, and the highest levels of species richness were found under intermediate environmental (disturbance, light conditions and temperature) conditions where there was a mixture of species from different biogeographic regions. In contrast to species richness, fine-scale phylogenetic diversity was negatively associated with the main vegetation gradient. The highest phylogenetic diversity was found in the extremely thin-soiled alvar grasslands in Gotaland and on the Baltic islands (especially on Oland) where the high phylogenetic diversity is likely to be a reflection of a long history of continuous openness that has allowed time for the "collection" of phylogenetically different species within these unique habitats. (C) 2012 Elsevier B.V. All rights reserved.

In the past, arable fields were established locally on the alvar on Oland. Several persisted until the present time, but some of them were abandoned shorter or longer ago. We found a series of arable fields forming a chronosequence: still cultivated, ca. 20 years abandoned, ca. 50 years abandoned, and never cultivated. Species of man-influenced habitats gradually disappeared from the former arable fields, but a few persisted after 50 years. A group of alvar species had re-established after 20 years, but others did not re-establish even after 50 years of abandonment, although they are present in the local species pool. We found no evidence of dispersal as a constraint for re-establishment.

Alvars are habitats characterised by thin soils on limestone bedrock. The largest alvar area in the world is the Stora Alvaret, Oland (25,500 hectares), which is characterised by the presence of several plant communities of high conservation value. Emigration at the end of the nineteenth century reduced land-use intensity resulting in scrub encroachment, mainly by Juniperus communis L. This later accelerated, leading to abandonment because grazing in the low-productivity pastures was uneconomic. Monitoring in permanent plots over a twenty-year period (1971-91) showed an increase in juniper cover over time and a clear correlation with a decline of other vascular plant species. This resulted in a gradual loss of both a valuable mosaic structure and a high level of bio-diversity in the landscape. An EU funded LIFE project (1996-99), which examined the effects of grazing and scrub clearance, is outlined. Various management techniques were tested and evaluated, providing valuable information for the present large-scale restoration and management programme supported by the European Union agri-environment schemes. In 1994 less than 60% of the Stora Alvaret was grazed. By 2005 this had increased to 98%. The reintroduction of grazing has resulted in a significant increase in the abundance of twelve out of 72 vascular species in permanent plots (1997-2001). Sheep and cattle numbers increased in Oland during the last decade, whereas they decreased in Sweden as a whole over the same period. Sixteen nature reserves have been established in Stora Alvaret, and a functioning alvar pasture landscape has been re-established. Almost all alvars in Oland have been designated as Natura 2000 areas. Ejvind Ros?n (e-mail: eje.rosen? ebc.uu.se), Uppsala University, Plant Ecology, Evolutionary Biology Centre, Villav?gen 14, SE-752 36 Uppsala, Sweden. INTRODUCTION This paper gives an overview of the vegetation and land-use history of limestone areas, called alvars, on the island of ?land. The word alvar refers to large areas with various thin deposits of soils, both calcareous and silicious, overlying the bedrock. With a few exceptions these areas are not suitable for cultivation but have been used as pasture for thousands of years. Alvars are mainly located on the Swedish islands of ?land (Rosen 1982; Bengtsson et al. 1988) and Gotland in the Baltic (Ekstam and Forshed 2002), but they also occur in Estonia and western Russia (Partei et al. 1999; Znamenskiy et al. 2006). Similar alvar landscapes occur in the Great Lakes region of Canada and the USA (Catling and Brownell 1995; Stark et al. 2003). *As an abbreviation in the text Stora Alvaret is referred to as Alvar, while alvar is used as a general term. Most attention will be given to the largest area, Stora Alvaret (The Great Alvar)*, covering 25,500ha, located in the southern part of the island. It occupies about half the area of the World Heritage Area known as 'The Agricultural Landscape of Southern Oland'. A total of c. 35,000ha are classified as alvars, however, including smaller areas in the eastern and northern parts of the island (Fig. 1). Alvars on the eastern side are usually part of the more productive grasslands in the coastal zone, while alvars in the north are mostly small and isolated. The latter are mainly located on the western side of the island, which is higher and drier than in the east, but with moist to wet areas occurring in depressions in the bedrock. Interspersed sand and gravel deposits often support small woodlands. Until the 1820s Stora Alvaret was a large commonage. After land reform, nearby villages received their own share of alvar land, which was then usually separated by stone walls. Since then almost all land has been privately owned. Recent land use changes, e.g. overgrazing, abandonment of Biology and Environment: Proceedings of the Royal Irish Academy, Vol. 106B, No. 2, 387-399 (2006). ? Royal Irish Academy 387 This content downloaded from 157.55.39.164 on Thu, 07 Jul 2016 04:43:22 UTC All use subject to http://about.jstor.org/terms Biology and Environment Fig. 1 ? The location of alvars on ?land, with Stora Alvaret in the southern part. Inset shows the location of ?land in the SW part of the Baltic. ?land is part of Kalmar county. grazing, scrub encroachment, etc. have resulted in major changes in landscape dynamics and loss of valuable habitats. The results of different restoration methods and their impact on conservation, as well as monitoring, are presented. BACKGROUND TO THE ECOLOGY OF OLAND

. Alvars in the Baltic region, particularly on the Swedish islands of Oland and Gotland and in western Estonia, are well-known for their plant species richness and extensive populations of rare species. Grasslands make up most of alvar vegetation. The extent of these grasslands decreases because of bush enchroachment which takes place in most alvars when traditional land use practice changes, notably when grazing is ceased. The main threat for the alvar grassland is formed by the rapid expansion of Juniperus communis and Potentilla fruticosa in dry and wet sites, respectively. Applied research has been carried out during several years in order to develop plans for the restoration of alvar grassland. Thus it was shown that species richness in areas with a mixture of grassland and shrubland decreases in relation to the increased cover by shrubs. In the case of Juniperus there is a distinct drop in species number as soon as the cover exceeds 75-80%, while the decrease is more gradual with increased cover of Potentilla. The seed banks under dense stands of these shrubs only contain ca. 20% of the species found in dry and wet alvar meadows. This was confirmed by clearing experiments. Long-term recordings have shown that establishment of juniper seedlings takes place mainly in half-open areas between already existing junipers. Intermediate-sized junipers expanded faster than old and big shrubs. Potentilla shrubs recover fast from cutting or burning. After 2-4 yr they have almost attained their former size. This recovery can be prevented when cattle grazing is introduced. In the framework of a local alvar restoration project on Oland, covering 7000 ha, grazing regimes are re-established, fences erected and large-scale clearings carried out. Recently established juniper shrubs are being cleared, intermediate sized junipers (30-50 yr old) are selectively removed while creating a mosaic landscape with high biological diversity. Older dense juniper stands are left alone or are only partly cleared. Potentilla stands in moist areas are cut to create moist meadows which are breeding grounds for waders, and to establish corridors between remaining open areas. Three items are discussed (1) the importance of the Stora Alvar area; (2) re-introduction of grazing and (3) re-introduction of species. The outstanding importance of the area regarding species richness and endemism should be recognized through a golden list to be used along with red and blue lists.

Changes in allozyme frequencies in populations of Festuca ovina after a ten-year fertilization experiment.

Dynamics of vegetation was studied on Stora Alvaret in Öland, Sweden, in comparison with precipitation in the May–July part of the growing period. Three data sets representing three main life forms (shrub, dwarf-shrub, and herbs) were collected. species composition eight grassland permanent plots (1969–1993, ass.Veronica spicata-Avenula pratensis), survival and health status ofJuniperus communis (1975–1993), andCalluna vulgaris cover at two permanent plots for the same period. Mortality ofJuniperus andCalluna and proportion of annual species were synchronized and correlated with severe droughts. *** DIRECT SUPPORT *** A02DO006 00003

Most theories of plant species coexistence assume the presence of diversity maintenance mechanisms, i.e. mechanisms enhancing species richness in a community. We wished to determine whether such a mechanism was operating by establishing a field experiment in the species-rich wooded meadow of Laelatu, western Estonia. Ten to seventeen subordinate species were removed periodically (for 4 years) from 10 permanent plots of 1×1 m (each plot had its specific list of excluded species; 10 plots served as control). Since the removed species were all subordinate ones, very little biomass was removed, but at the same time richness was reduced by 25–33%. If some diversity maintenance mechanism was operating, we would expect that immigration of other subordinate species would restore the original species richness.

In herbaceous plant communities of Stora Alvaret (the Great Alvar), Oland, Sweden, we studied the dependence of species-area relationships on the canopy cover of the colonizing shrubs Juniperus communis and Potentilla fruticosa. A series of plots 0.25 - 256 m2 in area were sampled in communities with varying canopy cover of Juniperus or Potentilla. Species number - log (area) regressions always fitted data better than log (species number) - log (area) regressions. The number of species declines more dramatically with increasing Potentilla cover than with increasing Juniperus cover. The total species number in large Juniperus plots follows a unimodal curve with a peak at about 75 % shrub cover. The alvar (limestone grassland) species number in plots of all sizes declines monotonically with Juniperus cover following the regression equation S = 31.09 + 10.75 log A - 0.0025 P2, where A is area and P is percentage Juniperus cover. There is a monotonic decline of species number with increasing shrub cover in Potentilla plots of all sizes. The species richness in plots with Potentilla was fitted by the regression equation S= 16.48 + 14.91 logA - 0.131 P - 0.00104 P2 log A, where P is % Potentilla cover. A faster initial decline of species number with Potentilla colonization is apparently caused by its preferential establisment in species-rich, elevated microsites.

The dry alvar grasslands of Oland: ecological amplitudes of plant species in relation to vegetation composistion.

Four plant community types are described for Öland's Stora Alvar, the limestone plateau of South Öland and preliminary classified syntaxonomically: (1) Crepis pumila – Allium alvarense ass. (2) Helianthemum oelandicum – Galium oelandicum ass. (3) Gypsophila fastigiata – Globularia vulgaris ass. and (4) Veronica spicata – Avenula pratensis ass. (with two subassociations, the Sedum reflexum and Galium boreale subass.). The ecology of these types is discussed with emphasis on soil depth, frost perturbation and the combined effects of summer drought and grazing intensity. Various endemic taxa appear to be good character species for the community types described. The typical local ecology of some common species is discussed with the suggestion that they might have formed endemic ecotypes which should be further investigated. The communities described are very rich in cryptogams. The floristic variation as expressed by the cryptogamic species composition shows largely the same pattern as that shown by the phanerogams.