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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.
We studied the dry grasslands of shallow, skeletal soils (Sedo-Scleranthenea, Koelerio-Corynephoretea) in northern Europe, based on a combination of new relevés from southern Oland (Sweden, n = 182) and Saaremaa (Estonia, n = 73) as well as a comprehensive evaluation of literature data, of which 65 suitable relevés were directly included in our analyses. Apart from a few vague indications of acidophytic Sedo-Scleranthenea communities (order Sedo-Scleranthetalia), all data refer to basiphytic communities (Alysso-Sedetalia); our analyses are thus focussed on the latter. The Nordic Alysso-Sedetalia communities proved to be quite different from their temperate counterparts and thus are included in a separate alliance, Tortello tortuosae-Sedion albi, which forms the northern counterpart to the central European Alysso-Sedion. Within the northern alliance, we distinguish two suballiances. The more widespread central suballiance Tortello tortuosae-Sedenion albi inhabits different types of base-rich substrata in both natural and anthropogenic sites, and is comprised of the Cladonio symphicarpiae-Sedetum albi and the Ditricho flexicaulis-Sedetum acris. The second suballiance Tortello rigentis-Helianthemenion oelandici is restricted to the alvar sites (= treeless limestone plateaus) in Oland, Gotland, Västergötland and Estonia. It is characterised by several endemic taxa and a large number of cryptogams typical of alvar. It is comprised of four associations, Crepido pumilae-Allietum alvarensis, Fulgensio bracteatae-Poetum alpinae, Helianthemo oelandici-Galietum oelandici and Gypsophilo fastigiatae-Globularietum vulgaris. All six Nordic associations are described in detail with respect to their floristic composition, ecology, distribution and lower-ranked units, and each is represented by a vegetation table. The floristic differences within the Nordic communities are worked out in a synoptic table. Whereas several vegetation scientists have pointed out that vegetation types occurring at the limits of their distribution ranges in northern Europe are generally difficult to classify, our application of the Braun-Blanquet approach, which is based on a priori separated structural types and the general application of the central syntaxon concept, has enabled us to characterise and adequately define all Nordic communities. The Tortello-Sedion associations are two to three times as species-rich as those of the Alysso-Sedion and are among the most diverse small-scale plant communities ever described. We discuss the reasons for this exceptionally high plant diversity and the peculiar species mixture in the Tortello-Sedion and compare the relationship between Alysso-Sedion and Tortello-Sedion to the situation of other Nordic syntaxa of predominantly temperate vegetation types. Our results further underline the uniqueness of Baltic alvars and their paramount importance for conservation at the European level.