04E1

E. Herbaceous communities and communities of lichens and mosses

Sub-continental petrophytic steppes

Relationships with habitat classifications. EUNIS: E1.222 Moesio-Carpathian steppes; PAL. CLASS.: 34.3161 Moesio-Carpathian steppes; HD 92/43: 6240 *Sub-Pannonic steppes; Bondev (1991): 129 Xerothermal grass communities with a prevalence of Dichantieta ischemi, Poaeta bulbosae, Poaeta cocinnae, Chrysopogoneta grylli and Ephemereta.

Conservation status. BDA, BC, HD

Category. Vulnerable [VU - A1, 2 B1 C2 D1 E2 F1 G1 H3 I].

General characteristics. Various petrophytic calcicole communities, syntaxonomically belonging to alliances Festucion valesiacae and Satureio-Thymion,order Festucetalia valesiaceae and class Festuco-Brometea. They occur in the continental regions to the North of the Balkan Range, most frequently on the open karst heights of the Forebalkan: the regions of Belogradchik, Montana, Vratza, Lovech and Veliko Tarnovo towns. The sub-continental petrophytic steppes in the loess areas of the Danubian Plain have their local peculiarities. They occur on the steep, right slopes of Osam, Yantra and Roussenski Lom rivers, where the basic karst rocks lay open. In Ludogorie area (NE Bulgaria), the sub-continental petrophytic steppes occur in the karst dry valleys, as well as on the slopes of the limestone plateaus near Shoumen, Provadia, etc. A gradual transition to the West-Pontic petrophytic steppes from the alliance Pimpinello-Thymion zigoidii is observed northeastwards.

High species diversity is typical for the sub-continental petrophytic steppes. The vegetation cover is uneven and various caespitose grasses, semi-shrubs, ephemers and ephemeroids prevail. Typically they develop on shallow, calcareous, very thin, sometimes absent, soil layer. Usually these areas are strongly eroded and cover steep slopes, with different, but mainly southern or western, exposure. The stability of the bed rock preconditions the specificities of the phytocoenoses.

The sub-continental petrophytic steppes occur on the rock “wreaths” of the canyon-like river valleys in N Bulgaria (Ogosta, Vit, Iskar, Yantra, Roussenski Lom rivers). The bed rock consists mainly of Cretaceous limestone and marls of different solidity and pore structure. Thin soil layer is formed in the fissures of the rocks where open herbaceous communities develop. Typically, in early spring the water coming from the adjacent areas is retained on the rock “wreaths” and hence spring aspects rich in mosses and lichen develop (Cladonia spp., Collema flaccidium, Grimmia pulvinata, Syntrichia ruralis). Consequently in hot and dry summers they pass through anabiosis. The calcareous screes are much drier than the “wreaths” and hence no such aspects develop. The sloping generally varies from 10 to 30–40º, and in steeper places the bed rock lays bare and typical hasmophytic communities are established. The total projective cover of the coenoses varies from 30 to ca. 60–70%. The species composition is a mixture of typical hasmophytes and species charactersitic for the closed coenoses of perennial grasses developing in the adjacent areas with better quality soil. Great species diversity and its geographical vicariation at short distances are typical for these coenoses. The floristic composition depends on the geographic situation, and on the bed rock - mobile screes, marl rocks and stones varying in size, or eroded, rocky slopes with poor soils. There are three types of habitats depending on these features:

These are the most widely distributed petrophytic steppes in Bulgaria. They occur mostly in the karst regions of Forebalkan on eroded Mesozoic (mostly Cretaceous) limestone. They are typical for Vedernik, Shiroka Planina, Verenishko Bardo, Milin Kamak, Pastrina, Vesletz mountains, Karlukovo karst area, Markova Mogila, Tuchenishko and Devetashko plateaus, Lovech, Sevlievo and Tarnovo heights, Polomie area, Preslav-Dragoevo mountain and some dry valleys in Ludogorie area. These habitats occur mostly on relatively stable rocky slopes, with shallow and eroded soil, above rocky canyons, gorges, etc. in the river valleys.

Many chamephytes (semi-shrubs and caespitose grasses) and terrophytes are typical for this habitat type. Satureja montana subsp. kitaibelii is the major dominant species. Alyssum saxatile, Astragalus onobrychis subsp. chlorocarpus, Dianthus petraeus subsp.noaeanus, Paronychia cephalotes, Potentilla pilosa, Seseli rigidum, Teucrium montanum, T. polium occur frequently. The participation of the regional endemic Seseli degenii is typical for Karlukovo karst area. Of the grasses, Bothriochloa ischaemum(= Dichanthium ischaemum, for which the eroded limestone places can be regarded as its primary habitat), Koeleria macrantha, Melica ciliata, Stipa pennata agg. and S. capillata are the most frequent grass species. Poa bulbosa and many other ephemeres and ephemeroids make the early-spring and spring aspects of the habitat. Very often Orlaya grandiflora forms a typical, late-spring – early-summer white aspect in many places. Also typical are Allium flavum, A. moschatum, A. sphaerocephalon,Alyssum parviflorum (= Alyssum minus), Arabis recta, Crupina vulgaris, Hyacinthella leucophaea, Muscari neglectum, Ornithogalum refractum, Saxifraga tridactylites. Various succulent species from Crassulaceae: Jovibarba heuffelii, Sedum hispanicum, S. maximum, S. urvillei are also typical. Due to the local temperature conditions (limestone reduces the microclimatic fluctuations of the area), many sub-Mediterranean species occur. They are mostly terrophytes like Coronilla scorpioides, Ononis pusilla, Salvia sclarea, Trifolium subterraneum, Trigonella gladiata.Such sub-Mediterranean “oases” on limestone are found in Devetashko Plateau, Lovech and Tarnovo heights where Artemisia alba, Euphorbia myrsinites and other species  typical for S Bulgaria and the Black Sea coast occur frequently in the composition of the petrophytic steppes. Almost always the petrophytic steppes with Achillea clypeolata, form complexes with different closed herbaceous and shrub coenoses. The shrub species – Amygdalus nana (very rarely), Carpinus orientalis, Cotoneaster integerrimus, Fraxinus ornus, Paliurus spina-christi, Rhamnus saxatilis, Syringa vulgaris occur in this steppes. The wide participation of the coenoses of Jerusalem thorn (Paliurus spina-christi) is typical for Forebalkan.

This habitat subtype is distributed on restricted areas in the central part of the Danubian Plain, lower part of the valley of Osam River (Nikopol plateau), Yantra river (to the North of the town of Byala) and in some places in the Polomie area (Ostritza village and others), where, local openings of cretaceous limestone and marls exist on the right banks of the rivers. Most frequently, this habitat subtype occurs on the most eroded places and white screes of Cretaceous limestone of Shoumen and Provadia-Royak plateaus and Suha River, where also a transition to the West-Pontic petrophytic steppes can be observed. Typical for their floristic composition is the combination of southern sub-Mediterranean elements with relic steppe species related to the West-Pontic petrophytic steppes. The late-spring, yellow aspect  of the yellow-flowering Linum tauricum is typical. Along Osam and Yantra rivers it is composed by the endemic subspecies Linum tauricum subsp. linearifolium. Characteristic species are Allium saxatile, Alyssum corymbosoides, Aster oleifolius, Cephalaria uralensis, Dianthus nardiformis, D.pseudarmeria, Ephedra distachya, Genista sessilifolia subsp. trifoliata, Goniolimon tataricum, Gypsophila glomerata, Iris pumila,Matthiola fruticulosa, Scutellaria orientalis subsp. pinnatifida. Common with the transitional type are Achillea clypeolata, are Achillea clypeolata, Allium moschatum, Euphorbia seguerana, Melica ciliata, Rhodax canus, Satureja montana subsp. kitaibelii (Nikopol region), Teucrium montanum. Some species are closely related with the habitat subtype under consideration, e.g. Salvia scabiosifolia, which dominates a small area on the right bank of Yantra river near Polsko Kossovo village. From Polomie area and eastwards, in the dry valleys of Dobudzha area, some vicariant changes occur in the species composition of the coenoses, e.g. Satureja montana is replaced by Satureja coerulea and the endemics Chamaecytisus jankae, Potentilla emilii-popii, Salvia ringens,etc. occur. Particularly specific are the white mobile screes of Shoumen and Provadia-Royak Plateaus. These screes are from clayey and glaconite limestons and calcareous marls (Upper Cretaceous age), that are on very steep and highly eroded ground. The coenoses that develop do not include grasses but only creeping, small, semi-shrubs and perennial herbs. Species from Pimpinello-Thymion zigoidii - Pimpinella tragium subsp.lithophila, Satureja coerulea, Thymus zygioides as well as from the West Pontic steppes (poorer species composition and lack of grasses) participate in their composition. Achillea clypeolata, Hedysarum tauricum, Lembotropis nigricans, Onosma visianii, Potentilla bornmuelleri also occur.

The petrophytic steppes dominated by Stipa tirsa are of limited distribution in Bulgaria. They occur in Central Danubian Plain, along Vit River (Riben village), Osam River (Nikopol plateau) and on the right bank of Studena River, to the north from Gorna Studena village. The so called “coilista” occurred also in the 1940s in NW Bulgaria but were destroyed. Stipa tirsa participates in the composition of open petrophytic coenoses in the limestone areas in the Forebalkan, but its coenoses dominated by this species coenoses are very rare. One of the main reasons for that is that Stipa tirsa cannot survive the competition of tuft grasses, especially Chrysopogon gryllus, that cover the places with well-developed soils. The Stipa coenoses are relic, and are preserved only in strongly eroded places, with limestone outcrops and poor or missing soil layer. Many Steppe and less sub-Mediterranean species together with species that occur also in the petrophytic steppes with Achillea clypeolata Participate in the floristic composition of this habitat subtype. To the group of the steppe species belong Adonis volgensis, Aster oleifolius, Astragalus austriacus, A. corniculatus, A. glaucus, A. pubiflorus, Centaurea stereophylla, Phlomis herba-venti subsp. pungens, Salvia nutans. To the other group belong Convolvulus cantabrica, Satureja montana. Some local endemics with steppe origin are also typical: Hedysarum grandiflorum subsp. bulgaricum, Serratula bulgarica. Petrophytic steppes with Stipa spp. are an edafic and relic phenomenon. This is proved by the fact that many steppe xerophytes participates in their floristic composition. Undoubtedly, in most steep and rocky places these coenoses are of primary origin. Possibly, after intensive grazing and secondary erosion they have increased their distribution in some places replacing forests or closed communities of caespitose grasses. Secondary petrophytic steppes have poorer species composition and their role in the vegetation cover of the country is insignificant.

Characteristic taxa.

Distribution in Bulgaria. Forebalkan, Ludogorie area (NE Bulgaria) and in isolated places in the central part of the Danubian Plain (Nikopol, Svistov and Rousse regions); up to ca. 1000 m alt.

Conservation importance. Vulnerable habitat of restricted distribution in Bulgaria that is subjected to various long-term threats. It is very important for the protection of numerous rare, endangered and protected steppe species. Most rare are: Adonis volgensis, Astragalus corniculatus, A. haarbachii,Ephedra distachya, Goniolimon tataricum,Hedysarum grandiflorums subsp. bulgaricum, H. tauricum,Nepeta parviflora,Polygala sibirica, Potentilla emilii-popii, Salvia scabiosifolia, Serratula bulgarica, S. radiata, Seseli degenii.The following fungi species of conservation concern Amanita vittadinii, Pisolithus arhizos also occur.

Threats. Major threats are intensive grazing that stimulates erosion processes and hence change in the species composition; terracing and forest planting; natural landslides. The exploitation of limestone and marl, mainly in Forebalkan region, has a very negative impact.

Conservation measures taken. The habitat is included in Annex № 1 of the national Biodiversity Act. Parts of these habitat type are within the borders of protected areas: Roussenski Lom Nature Park, Chernelka Nature Monument and others. Most of the steppe coenoses are within the borders of protected zones of the European Ecological Network NATURA 2000 in Bulgaria.

Conservation measures needed. Monitoring of the state of the habitat and regulation of the exploitation of limestone, clays and marls.

References. Jordanoff 1936; Tzonev 2002.

Author: Rossen Tzonev


Sub-Continental petrophytic steppes (distribution map)