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Dry grasslands of NW Bulgarian mountains : first insights into diversity, ecology and syntaxonomy
(2013)
We present the data of the 3rd research expedition of the European Dry Grasslands Group (EDGG), which was conducted in 2011 in two contrasting areas in NW Bulgarian mountains. The aim was to collect plot data for comparing Bulgarian dry grasslands with those of other parts of Europe in terms of syntaxonomy and biodiversity. We sampled 15 nested-plot series (0.0001–100 m²) and 68 normal plots (10 m²) covering the full variety of dry grassland types occurring in the Vratsa area (Balkan Mts.) and the Koprivshtitsa area (Sredna Gora Mt.). In the plots all vascular plants, terricolous non-vascular plants and a set of soil and other environmental parameters were determined. By applying modified TWIN-SPAN, we distinguished 10 floristically well characterised vegetation types at the association level. After comparison with the regional and European literature, we propose to place them within three classes and five orders: Festuco-Brometea with the orders Stipo pulcherrimae-Festucetalia pallentis (xerophilous dry grasslands of base-rich rocks; alliance Saturejion montanae), Brachypodietalia pinnati (meso-xeric, basiphilous grasslands; alliances Cirsio-Brachypodion pinnati and Chyrsopogono grylli-Danthonion calycinae), Calluno-Ulicetea with the order Nardetalia stricae (lowland to montane Nar-dus swards; alliance Violion caninae), and Koelerio-Corynephoretea with the orders Sedo-Scleranthetalia (open communities of skeleton-rich, acidic soils; alliance unclear) and Trifolio arvensis-Festucetalia ovinae (closed, meso-xeric, acidophilous grasslands; alliance Armerio rumelicae-Potentillion). The Violion caninae with the association Festuco rubrae-Genistelletum sagittalis is reported from Bulgaria for the first time, while the two occurring Koelerio-Corynephoretea communities are described as new associations (Cetrario aculeatae-Plantaginetum radicatae, Plantagini radicatae-Agrostietum capillaris). According to DCA the main floristic gradient was largely determined by soil conditions, differentiating the Festuco-Brometea communities on soils with high pH and high humus content from the Koelerio-Corynephoretea communities on acidic, humus-poor soils, while the Calluno-Ulicetea stands are the connecting link. At 10 m2 Festuco-Brometea and Calluno-Ulicetea stands were richer in species across all investigated taxa and in vascular plants than Koelerio-Corynephoretea stands; the latter were richest in lichen species, while bryophyte richness did not differ significantly among syntaxa. Among the Bulgarian classes, the species-area relationships tended to be steepest in the Festuco-Brometea (i.e. highest beta diversity), but both alpha and beta diversity clearly fell behind the Festuco-Brometea communities in the Transylvanian Plateau, Romania, located less than 500 km north of the study region. Overall, our study contributes to a more adequate placement of the Bulgarian dry grasslands in the European syntaxonomic system and provides valuable data for large-scale analyses of biodiversity patterns.
Dry calcareous grasslands in Europe are renowned for their high plant diversity. However, declining habitat areas and highly fragmented distribution threaten the long-term persistence of this valuable habitat type. In Estonia the decline of traditional grassland management and subsequent encroachment of shrubs has resulted in a substantial loss of alvar grasslands – a particularly rare and species-rich type of calcareous grassland. It is known that a shrub cover of more than 70% decreases the alvar grassland species richness. At the same time, a shrub cover of 30% is considered optimal for alvar grasslands and thus a target state for habitat restoration. However, very little is known about the effect of low shrub cover on environmental conditions and species composition of alvar grasslands. Our aim was to detect to what extent the small-scale plant diversity and species composition is influenced by low shrub cover (less than 30%). We hypothesized that even a low shrub cover can have an effect on the environmental conditions of alvar grasslands. We sampled small-scale plant species richness, shrub cover and abiotic environmental conditions such as light, soil moisture, soil pH and soil depth in 10 metre long transects (n = 33) subdivided into 10 cm × 10 cm plots in Estonian alvar grasslands. Structural equation modelling was used to quantify the direct and indirect effects of shrub cover on the richness of characteristic alvar species and on the richness of generalist species. We found that low shrub cover of up to 30% increased total and generalist species richness directly and indirectly by increasing the light heterogeneity. Alvar characteristic species richness was not relat-ed to low shrub cover values. This suggests that when estimating the effects of shrub cover on species richness and on conservation needs of grasslands, habitat specificity of species needs to be taken into account.