03E1

E. Herbaceous communities and communities of lichens and mosses

Sub-Mediterranean petrophytic steppes

Relationships with habitat classifications. EUNIS: E1.55 Eastern sub-Mediterranean dry grasslands; PAL. CLASS.: 34.75 Eastern sub-Mediterranean dry grasslands; HD 92/43: 62A0 Eastern sub-Mediterranean dry grasslands (Scorzoneratalia villosae); Bondev (1991): 129 Xerothermal grass communities with a prevalence of Dichantieta ischemi, Poaeta bulbosae, Poaeta cocinnae, Chrysopogoneta grylli and Ephemereta.

Conservation status. BDA, HD.

Category. Vulnerable [VU – A1, 2 B2 C1 D1 E2 F G H3 I L2].

General characteristics. Diverse petrophytic calcicole communities distributed mainly in areas with transitional Mediterranean climate: hills in the Thracian Lowland and Toundzha Hilly Country, East Rhodopi Mts, the valley of Mesta River and on the slopes of Pirin, Slavyanka and Stargach Mts; in isolated places in Strandzha Mts and South Black Sea coast, Central Rhodopi Mts and the southern slopes of the Balkan Range and Sredna Gora Mts.

Great floristic diversity is typical for the southern Bulgarian sub-Mediterranean petrophytic steppes. Various caespitose grass species, semi-shrubs, ephemeres and ephemeroids prevail and the representatives of the last two groups increase with the increasing influence of the Mediterranean climate. The phytocoenoses develop on areas with open rock outcrops with very thin or absent soil layer. The bed rocks are limestones, marls, and in some places marbles of different geological age, of different solidity and pore structure. The slope of the areas normally varies from 20 to 30–40º. On steep slopes, due to erosion, typical hasmophytic coenoses develop on the open bed rock. The total cover of the coenoses varies from 30 to about 60–70%. The species composition is a mixture of typical hasmophytes and species typical for the closed coenoses of perennial grasses that occupy the adjacent areas with well developed soil layer. Ephemeres and ephemeroids are mainly of Mediterranean origin. Among grasses the prevailing species are mostly caespitose plants that grow in places with a preserved soil layer. Agropyron cristatum,Bothriochloa ischaemum(= Dichanthium ischaemum), Briza humilis, Festuca valesiaca, Koeleria simonkaii, Melica transsilvanica, Stipa capillata are most frequently encountered. Due to the more humid climate Chrysopogon gryllus participates in the composition of the petrophytic steppes in Strandzha Mts. Perennials that are widely distributed in karst areas in the whole country (Achillea clypeolata, Convolvulus cantabrica, Dianthus gracilis, Fumana procumbens, Genista depressa, Inula aschersoniana, Onobrychis lasiostachya, Rhodax canus, Sanguisorba minor, Satureja coerulea, Teucrium polium) and species  that are rarer and mostly of Mediterranean origin (Alyssum tortuosum, Andrachne telephioides,Asyneuma anthericoides, Euphorbia myrsinites, Hypericum olympicum, H. rumeliacum, Medicago coronata, Paronychia kapela, Thymus longedentatus) occur. Some regional endemics such as Achillea ageratifolia, Alkanna stribrnyi, Galium rhodopeum, Medicago rhodopea, Minuartia rhodopaea, Polygala rhodopea, Ranunculus sprunerianus, Thymus thracicus, and Verbascum nobile occur in the Rhodopi foothills. Veronica turrilliana occurs in Strandzha Mts. In East Rhodopi Mts. and in some place in SW Bulgaria Satureja coerulea is replaced by its vicariant S. pilosa.

The number of species of pontic origins(Allium flavum, Cephalaria uralensis, Iris pumila, Linum tenuifolium, Potentilla astracanica, Ruta graveolens, Scabiosa argentea)is relatively small in contrast to the Western-Pontic and Western-Bulgarian mountain petrophytic steppes. In the Strandzha Mts, the relic species Sideritis syriaca participates in the coenoses of the Southern-Bulgarian sub-Mediterranean petrophytic steppes. The petrophytic steppes in Sakar Mt and Dervent hills are very specific because some species typical for the Western-Pontic steppes occur there: Koeleria brevis, Paeonia tenuifolia, etc. The participation of steppe elements increases in SE Bulgaria northwards of Bourgas, near the towns of Kameno and Balgarovo and on the southern slopes of Aitos mountain.

The group of annuals (ephemeres) is large and consists mainly of species of southern origin, including some very rare species for which Bulgaria is the northernmost area of distribution in Europe. These are Asterolinon linum-stellatum, Clypeola jonthlaspi, Crucianella graeca, Euphorbia taurinensis, Hippocrepis ciliata, Lathyrus saxatilis, Lens nigricans, Queria hispanica, Scandix australis, Trigonella gladiata, T. monspeliaca, and Velezia rigida. The group of annual grasses is very specific and illustrates the relationship with the pseudosteppes from class Thero-Brachypodietea, with which the petrophytic steppes form complex plant communities. More typical ephemeres are Avena clauda,Desmazeria rigida, Echinaria capitata, Poa bulbosa, Psilurus incurvus, Trachynia distachya(= Brachypodium distachyon). More frequent among ephemeroids are Crocus spp., Hyacinthella leucophaea, Iris pumila, I. suaveolens, Muscari spp., Ornithogalum spp. In some places (Bessapara hills) Asphodeline lutea forms the late spring yellow aspect.

The petrophytic steppes participate in many complex communities and their representativeness depends on the slope slant, degree of soil erosion and the participation of perennial and annual grasses. These complexes encompass together with the petrophytic steppes small in size coenoses dominated by succulents and grass terrophytes (Thero-Brachypodietea); close coenoses dominated by perennial grasses (Bothriochloa ischaemum(= Dichanthium ischaemum), Chrysopogon gryllus), and various shrub and tree communities rich in Mediterranean, including evergreen, species (Jasminum fruticans, Juniperus oxycedrus, Paliurus spina-christi,Phillyrea latifolia, Pistacia terebinthus).

In many places, the Southern Bulgarian sub-Mediterranean petrophytic steppes are maintained by grazing, although intensive grazing may cause erosion and impoverishment of their species composition.

The Southern Bulgarian sub-Mediterranean petrophytic steppes are an edafic phenomenon. In most places with steep and rocky areas and natural erosion they are of primary origin. In many places with destroyed wood vegetation, intensive grazing has caused secondary erosion that has caused the expansion of the petrophytic steppes. Often the two types of steppes (according to their origin) can be observed together. The species composition of the secondary petrophytic steppes is poorer, with lower number of ephemeroid species thus representing a poorer derrivative of the closed steppe coenoses.

Characteristic taxa.

Distribution in Bulgaria. The southern Bulgarian sub-Mediterranean petrophytic steppes occur mainly in Thracian Lowland (Bessapara hills, Chirpan heights), Toundzha Hilly Country (incl. Dervent hills), lower, calcareous, eastern parts of Central Rhodopi Mts., Sakar and Strandzha Mts, South Black Sea coast, southern slopes of the Balkan Range, and Sredna Gora Mts, valley of Struma River and valley of Mesta River (on the slopes of Pirin, Slavyanka and Stargach Mts.) up to ca. 1000 m alt.

Conservation importance. Vulnerable habitat in Bulgaria, very important for the conservation of many rare and endemic xerophytic species of southern origin such as Aethionema arabicum, Andrachne telephioides, Asterolinon linum-stellatum, Crocus olivieri, Fibigia clypeata, Lathyrus saxatilis, Linum thracicum, Merendera attica, Moehringia grisebachii, Polygala rhodopea, Romulea linaresii, Ruta graveolens, Scandix australis, Verbascum humile, V. nobile, Veronica turrilliana, etc..

Threats. Most important threats are overgrazing (increases erosion and changes in the species composition), terracing and forest planting. The exploitation of limestones and marls has a very strong negative impact.

Conservation measures taken. The habitat is included in Annex № 1 of the national Biodiversity Act. Some of the localities are within the borders of protected areas: Strandzha Nature Park, Ognyanovsko-Sinitevski Rid Protected Site, etc. Most of the steppe coenoses are within the borders of the European Ecological Network NATURA 2000 in Bulgaria: Bessapara hills, Strandzha, Sakar, Dervent hills, East Rhodopi zones, etc.

Conservation measures needed. Regulation of the exploitation of limestone, clay, marls. Expansion of existing (Bessapara hills) and proclamation of new protected areas in some of the most representative localities of these steppes.

References. Stanev 1977a, b.

Authors: Rossen Tzonev, Marius Dimitrov, Chavdar Gussev


Sub-Mediterranean petrophytic steppes (distribution map)