13G1

G. Forests

Thracian forests of White oak (Quercus pubescens)

Relationships with habitat classifications. EUNIS: G1.7371 Thracian White oak–Oriental hornbeam woods; PAL. CLASS.: 41.7371 Thracian White oak–oriental hornbeam woods; HD 92/43: 91AA *Eastern White oak woods; Bondev (1991): 106 Querceta pubescentis and Virgilian oak (Querceta virgiliane) forests, 107 Querceta pubescentis and Virgilian oak (Querceta virgiliane) forests with Mediterranean elements, 110 Mixed Quercus pubescens, Virgilian oak (Querceta virgiliana) and Flowering ash (Fraxinus ornus) forests, 111 Mixed Quercus pubescens, Virgilian oak (Querceta virgiliana) and Oriental hornbeam (Carpinus orientalis) forests partly of secondary origin, 112 Mixet Quercus pubescens, Virgilian oak (Querceta virgiliana) and Oriental hornbeam (Carpinus orientalis) forests with Mediterranean elements.

Conservation status. BDA, BC, HD.

Category. Endangered [EN – A1, 2 C2 D2 E2 F2 G2 H2 I L3].

General characteristics. This habitat type encompasses the xerothermic forests of White oak (Quercus pubescens) that occur in places with transitional Mediterranean, transitional continental and Euxinian climate. They are distributed in South Bulgaria – mainly in the Thracian Plain, Toundzha Hilly Country, East Rhodopi Mts., Black Sea Coast and the valleys of Struma and Mesta rivers. These forests are a part of the mixed oak forests that usually occupy the driest and warmest slopes with southern or western exposures. The soils are poor and eroded, most often different types of the shallow Leptosol - Lithic Leptosols, Rendzic Leptosols and Umbric Leptosols, and in some places, Chromic Luvisols. The bedrock varies, e.g. limestone and marble in Thracian Plain and Toundzha Hilly Country and different types of basic rocks in the southernmost parts of Bulgaria – East Rhodopi Mts (volcanic tufts, riolites, andesites, etc.) and the valley of Struma river (gneiss, amphibolites, etc.). Rock outcrops of different size often appear on the surface.

These forests are thin, light and are in a stage of anthropogenic degradation. The impact of human and domestic animals on their structure is heavy. Many tree, shrub and herbaceous species that participate in them enter from the neighbouring forests, meadows, scrub and open rocky areas. Among them are species that are widely distributed in the xerothermic communities in Bulgaria and species that are of more southern (Mediterranean) origin. The highest number of the second group is in the southern parts of the country, especially in East Rhodopi Mts. and along the valley of Struma river. The tree layer dominated by the White oak is a dominant or co-dominant reaches 5–6 m. The trees are branched, often with crooked trunks. Apart from Quercus pubescens,also Acer campestre, A. hyrcanum, A. monspessulanum, Fraxinus ornus, Pistacia terebinthus, Quercus cerris, Q. dalechampii, Q. frainetto, and Q. virgilliana occur in this layer. Carpinus orientalis plays a more important coenotic role in the continental forests of White oak. In most coenoses of this habitat type it is a codominant and on more eroded and poor soils the White oak is replaced by monodominant scrub communities of Carpinus orientalis. Colutea arborescens, Cornus sanguinea, Coronilla emerus subsp. emeroides, Cotinus coggygria, Crataegus monogyna, Juniperus oxycedrus, Paliurus spina-christi, Syringa vulgaris play an important role in the shrub layer of the white oak forests. Phillyrea latifolia occurs also in some places.Mainly species typical for the xerothermic oak forests, among which many Mediterranean species, occur mainly in the herbaceous layer. This rich species complex includes Althaea cannabina, Anacamptis pyramidalis, Aristella bromoides (= Stipa bromoides), Asparagus verticillatus, Aster amellus, Avenula compressa, Brachypodium pinnatum, B. sylvaticum, Buglossoides purpurocaerulea, Comandra elegans, Dactylis glomerata, Dictamnus albus, Festuca heterophylla, Filipendula vulgaris, Geranium sanguineum, Helleborus odorus, Himantoglossum hircinum, Hypericum degenii, H. olympicum, H. rumeliacum, Inula ensifolia, Orchis purpurea, Phleum phleoides, Potentilla micrantha, Primula veris, Saponaria glutinosa, Tanacetum corymbosum, Teucrium chamaedrys, Thalictrum minus, and Trifolium alpestre.Different perennial grass species as well as terrophytes and hasmophytes grow in the most open and stony places. They penetrate from the neighbouring herbaceous communities. Agrostis capillaris, Bothriochloa ischaemum (= Dichanthium ischaemum), Chrysopogon gryllus, Festuca rupicola. Achillea clypeolata, A. depressa, Crucianella graeca, Genista carinalis, G. rumelica, Petrorhagia illyrica, Thymus striatus, Verbascum humile belong to the second group. Paeonia peregrina occurs in some forests of White oak in in East Rhodopi Mts. for instance, and in the forest – groupings of Cistus incanus (See Sub-Mediterranean garrigues).

The forests on the heights of Thracian Lowland, Toundzha Hilly Country and the southern slopes of Sredna Gora Mts. (near Stara Zagora) develop in the conditions of a transitional continental climate. They exhibit a mixture of characteristics of the continental and Mediterranean coenoses of this habitat type. Species typical for the xerothermic oak forests prevail in their composition together with some Mediterranean species that are absent in similar phytocoenoses in North Bulgaria. Such are Arum orientale, Clematis viticella, Jasminum fruticans. Paliurus spina-christi has more important role in the shrub layer compared to the white oak forests in North Bulgaria. White oak forests constitute always a complexes with other types of xerothermic oak forests mainly the forests with Quercus frainetto, Carpinus orientalis and in Kresna gorge – with Juniperus excelsa. Usually, in eroded, sunny places where these forests occur, they alternate with scrub of Juniperus oxycedrus, Paliurus spina-christi, Syringa vulgaris,with open herbaceous coenoses of Bothriochloa ischaemum(= Dichanthium ischaemum), Chrysopogon gryllys, Festuca rupicola, with open, rocky (silicate or limestone) areas and coenoses of terrophytes and succulents. As a result of degradation processes the White oak forests are usually replaced by secondary coenoses of Oriental hornbeam, Smoke tree, Prickly Juniper and very often of Jerusalem Thorn. Herbaceous coenoses with Chrysopogon gryllus, Festuca rupicola, and F. valesiaca also enter these forests. All these degradation processes are the consequence of anthropogenic activities – grazing, logging, fires.

Characteristic taxa.

Distribution in Bulgaria. South Bulgaria – mainly the heights in the Thracian Plain and Toundzha Hilly Country, East Rhodopi Mts, the valleys of Struma and Mesta rivers, and in the South Black Sea coast; up to approx. 800 m alt.

Conservation importance.  Forests of White oak are a habitat that occurs more and more rarely in Bulgaria as a result of logging, grazing, fires and natural degradation processes and erosion. In the White oak forests in Thracian Plain some endangered and protected species occur such as Achillea thracica, Andrachne telephioides, Aristolochia rotunda, Astracantha thracica (= Astragalus thracicus), Carduus thracicus, Fritillaria pontica, Heptatptera triquetra, Himantoglossum hircinum, Limodorum abortivum, Ononis adenotricha, Ophrys spp., Smyrnium rotundifolium, Stefanoffia daucoides, Vicia laeta. Fungi of conservation importance also occur – Amanita caesarea, A. franchetii, A. ovoidea, A. strobiliformis, Boletus dupainii, B. regius, B. rhodopurpureus, B. rhodoxanthus, B. satanas, Geastrum triplex, Hygrophorus russula, Leucopaxillus compactus, Pulveroboletus gentilis, Sarcosphaera coronaria, Tricholoma acerbum.

Threats. Clear cuttings and selection cuttings by the local people; replacement by forest plantations of species not typical for the area (Black pine and Scots pine), intensive grazing (mainly goats), fires, general aridisation of the climate, building of communication and transport networks (roads, rail ways, etc), quarries and open mines (especially in East Rhodopi Mts.), erosion.

Conservation measures taken. The habitat is included in Annex №1 of the Biodiversity Act. Parts of the White oak forests are within protected areas – e.g. in the area of Madzharovo and Studen Kladenets dam, Strandzha Nature Park, Meandrite na Byala Reka Protected Site, Tissata and Ropotamo Strict Nature Reserves. Some of the most representative white oak forests are in sites of the European Ecological Network NATURA 2000 in Bulgaria.

Conservation measures needed. Restriction of the factors that have negative impact on the ecosystems – grazing, clear cuttings, fires; involvement of the local people in the restoration of these forests through their sustainable use; management of the forests aiming at their transformation into seed forests and improvement of their health state through the implementation of suitable forest engineering practices; termination of forest reconstruction and planting of unsuitable species; restoration, mapping and monitoring of all preserved coenoses; proclamation of some of the representative coenoses of White oak as protected areas.

References. Ganchev 1965; Radkov & Minkov 1963; Stanev 1986.

Authors: Rossen Tzonev, Georgi Gugushev, Petar Zhelev


Thracian forests of White oak (Quercus pubescens) (distribution map)