05G1
Riparian and lowland mixed woodlands and longozes
Relationships with habitat classifications. EUNIS: G1.2232 Helleno-Balkan ash-oak-alder forests; PAL. CLASS.: 44.4322 Coastal Bulgarian longos forests, 44.4323 Central Balkan ash-oak-alder forests; HD 92/43: 91F0 Riparian mixed forests of Quercus robur, Ulmus laevis and Ulmus minor, Fraxinus excelsior or Fraxinus angustifolia, along the great rivers (Ulmenion minoris); Bondev (1991): 140 Querceta pedunculiflorae and Querceta roboris forests, partly mixed with field maple (Acer campestre), 142 Field elm (Ulmeta minoris) and field ash-tree (Fraxineta oxycarpae) forests.
Conservation status. BDA, HD, BC.
Category. Critically endangered [CR – A1, 2 B1 C2 D3 E3 F3 G3 H2 I J L2].
General characteristics. The mixed lowland and riparian forests and longoses are a part of the intrazonal vegetation distributed in the valleys of a number of Bulgarian rivers. Typical is the periodical flooding and in some cases high air humidity. The soil may be dry or wet between the floods. The dominant tree species depend on the water regime but most often are from the genera Fraxinus, Ulmus or Quercus. The herbaceous layer is well developed, with diverse species composition, and has been formed under the impact of the zonal vegetation. The mixed lowland riparian forests and longoses belong to class Populetea albae orders Fraxinetalia and Populetalia, and alliances Alno-Quercion roboris and Alnion incanae. Three subtypes can be distinguished.
Subtypes:
- Longos forests (association Smilaco excelsae-Fraxinetum oxycarpae)
The presence of many species with winding stems (lianas) is the reason why these forests are called longos. Their origin is related to specific climatic, hydrological, historical and phyto-geographical conditions. The longos forests are young and have been formed on Quaternery sediments and rich, humid and deep Fluvisols and Gleysols. These forests have originated at the end of the Quaternary period (beginning of the Holocene), when a rapid increase of the temperature and humidity began. They are typical for the transitional continental and Mediterranean climate with mild and humid winters. Therefore some evergreen and thermophilic species also occur in them and distinguish them from the remaining riverside forests in Bulgaria. This is the reason why these forests occur mainly in places close to the Black Sea, in the valleys of Veleka, Ropotamo, Kamchia, Batova rivers where the sea makes the climate milder. Locally these forests occur also in the valley of Toundzha River and in the Thracian Lowland. Water layers of different depth develop as a result of the spring floods. After 1-1,5 months the water flows to the rivers and in summers the humidity is provided by the high underground waters. The tree layer includes Acer campestre, Alnus glutinosa, Fraxinus oxycarpa, F. pallisiae, Populus alba, P. nigra, Quercus robur, Salix alba, Ulmus laevis, U. minor. The shrub layer includes Acer tataricum, Cornus sanguinea, Crataegus monogyna, Euonymus europaeus, Ligustrum vulgare and Prunus padus. The presence of climbing plants with woody and herbaceous stems is typical for these forests: Calystegia sepium, Clematis vitalba, Hedera helix, Humulus lupulus, Periploca graeca, Smilax excelsa, Tamus communis and Vitis sylvestris. The lianas make the forests impenetrable and they look like wet tropical forests. The herbaceous cover is of inconstant composition depending on the local peculiarities and dynamic processes. The preservation of high soil humidity and the dense shadow limit the development of a herbaceous cover in which also some ruderals participate. Most often dominants are Brachypodium sylvaticum, Galium aparine, Geum urbanum, Poa sylvicola, etc. Specific species for the spring ephemeroid synusium are Dactylis glomerata subsp. lobata, Fritillaria pontica, Leucojum aestivum,Primula vulgaris subsp. sibthorpii, Scilla bithynica. Ruderals and hydrophytes occur in the places with prolonged floods. The most frequent ruderals are: Galium aparine, Parietaria erecta (= Parietaria officinalis), Rumex sanguineus, Stellaria media, Urtica dioica. In places where the water is preserved for a longer time plant groupings of hygrophytes and hygromesophytes develop: Elymus repens, Iris pseudacorus, Lythrum salicaria, Mentha spp., Physalis alkekengi, Poa sylvicola, Potentilla reptans, Ranunculus repens, Symphytum officinale, etc.
- Humid lowland oak forests (association Scutellario altissimae-Quercetum roboris)
Multi-layered forests dominated by Quercus robur or Quercus pedunculiflora. Lianas also participate but they are less than in the longos forests. The species diversity in the herbaceous layer is relatively low. The spring, ephemeroid synusium is well developed. In the recent past these forests were widely distributed everywhere in suitable places in the Danubian plain and NE Bulgaria (Ludogorie region). The local inhabitants used to call them “ormani” or “elii”. They have been widely destroyed and turned into arable land in the last 50 years. Today, only groups of trees or solitary centurial trees occur in the places where these forests were distributed in the past. The altitude varies from 40 up to 70 m, the area is flat. The soils are Fluvisols, with good humidity, of gravel or sandy type, shallow, but with well-developed humus horizon. In the past, before the dikes were built, these places were flooded by the spring high waters (April – May). The break of the connection with the river has resulted in the disturbance of the hydrological regime, reduction in the forest canopy and the distribution of many alien species. The first tree layer consists of Fraxinus oxycarpa, Pyrus pyraster and Quercus robur. The trees of Quercus robur are far from each other but they dominate in height over the remaining trees. Ulmus minor, Acer tataricum and Acer campestre form the second, lower tree layer. The shrub layer includes Crataegus monogyna, Cornus mas, Corylus avellana, Ligustrum vulgare. Anemone ranunculoides, Arum maculatum, Brachypodium sylvaticum, Buglossoides purpurocaerulea, Corydalis bulbosa, Dactylis glomerata, Gagea minima, Galium aparine, Geum urbanum, Isopyrum thalictroides, Physalis alkekengi, Polygonatum latifolium, Pulmonaria officinalis, Rubus caesius, Scilla bifolia, Scutellaria altissima and Viola odorata occur frequently with differen abundance in the ground layer. Some shadow-resistant anthropophytes such as Aristolochia clematitis, Calystegia sylvatica, Heracleum sibiricum, Physalis alkekengi, Smyrnium perfoliatum, Urtica dioica also occur. Most often these forests have common borders with the riverside willow and poplar forests, but occupy drier places.
- Thracian forests of Quercus pedunculiflora. The Thracian forests of Quercus pedunculiflora are the driest subtype of the habitat of lowland riparian forests. In most cases they are old forests that occur on relatively small areas and are surrounded by agricultural land. In the past they occurred along Maritsa and Toundzha rivers and their feeders, and in the lowlands of S Bulgaria. Like the humid lowland oak forests they were called “ormani”, “elii”, etc. Nowadays, only single forest localities have survived. Most of them are the so called “zashtiteni korii.” They comprise solitary trees or groups of centurial trees in Thracian Lowland – Aitoska Korya, Yulevska Korya (Kazanlak region) and in Toundzha Hilly Country – Sliven and Nova Zagora regions, Chekeritsa forest near Plovdiv, near Navasen village, etc. The Thracian forests of Quercus pedunculiflora occur on humid and fresh soils, mainly Fluvisols, and more rarely on Vertisols and Chernozems. The areas are flat with shallow underground water. The primary structure of these forests included two tree layers, one shrub and one herbaceous layer, but in most places this structure is destroyed. The tree layer is dominated by Quercus pedunculiflora and Q. robur. Acer campestre, Pyrus pyraster, Ulmus minor also occur. In more humid places Fraxinus oxycarpa occurs, and in drier places solitary trees of Quercus cerris, Tilia spp. and even Carpinus orientalis occur. Sometimes there is a second tree layer formed by Acer tataricum. Crataegus monogyna, Cornus mas, Corylus avellana, Euonymus europaeus, Ligustrum vulgare, Rosaspp., Sambucus nigra prevail in the shrub layer. In more humid places Rubus spp. also occurs. Some lianas also occur, such as Clematis vitalba, Humulus lupulus, Vitis sylvestris, but they are considerably less frequent than in the longos forests. The herbaceous layer includes many spring-flowering species, Anemone ranunculoides, Ficaria verna (= Ranunculus ficaria), Polygonatum spp., Ranunculus constantinopolitanus, Scilla bifolia, and Viola odorata. Later in the year Arum elongatum, Buglossoides purpurocaerulea, Galium aparine, Geum urbanum, Scutellaria altissima, Smyrnium perfoliatum, Urtica dioica, etc. also occur.
Characteristic taxa.
- Vascular plants: 1. Alnus glutinosa, Arum orientale, Brachypodium sylvaticum, Cucubalus baccifer, Fraxinus oxycarpa, F. pallisiae, Fritillaria pontica, Galium aparine, Geum urbanum, Hedera helix, Humulus lupulus, Leucojum aestivum, Lysimachia nummularia, L. punctata, Nectaroscordum siculum (= Allium siculum), Parietaria erecta, Periploca graeca, Poa sylvicola, Populus alba, P. nigra, Prunus padus, Quercus robur, Rumex sanguineus, Scilla bithynica, Smilax excelsa, Solanum dulcamara, Stellaria media, Tamus communis, Ulmus laevis, U. minor, Urtica dioica, Vitis sylvestris; 2. Acer tataricum, Anemone ranunculoides, Buglossoides purpurocaerulea, Ficaria verna (= Ranunculus ficaria), Fraxinus oxycarpa, Geum urbanum, Polygonatum spp., Quercus cerris, Q. pedunculiflora, Q. robur, Ranunculus constantinopolitanus, Scilla bifolia, Scutellaria altissima, Smyrnium perfoliatum, Tilia spp., Ulmus minor, Urtica dioica, Viola odorata; 3. Acer campestre, A. tataricum, Alliaria petiolata, Arum elongatum, Buglossoides purpurocaerulea, Cornus sanguinea, Dactylis glomerata, Galium aparine, Geum urbanum, Ligustrum vulgare, Quercus cerris, Q. pedunculiflora, Ulmus minor.
- Fungi: Macromycetes – Agrocybe cylindracea, Auricularia mesenterica, Calycina alniella, Clathrus ruber, Coprinus disseminatus, Coriolopsis trogii, Cyathus striatus, Exida glandulosa, Flammulina velutipes, Ganoderma lipsiense, Hebeloma pumilum, Helvella elastica, Hypsizygus ulmarius, Inonotus dryadeus, Lachnum virgineum, Lacrymaria lacrymabunda, Lactarius controversus, Laetiporus sulphureus, Lenzites warnieri, Morchella esculenta, Omphalina discorosea, Oxyporus populinus, Phellinus igniarius, Pholiota aurivella, P. populnea, Pleurotus cornucopiae, P. ostreatus, Polyporus squamosus, Psathyrella candolleana, Tricholoma populinum, Volvariella bombycina; Micromycetes – Erysiphe urticae (on Urtica dioica), Gnomonia ditopa, Phyllactinia guttata, Plagiostoma alneum, Septoria alni (on Alnus glutinosa), Melampsora allii-populina, Septoria populi (on Populus nigra), M. populnea (on P. alba and P. nigra), Microsphaera alphitoides (on Quercus robur), Plasmopara viticola (on Vitis sylvestris), Podosphaera aphanis (on Geum urbanum), Pseudoperonospora humili, Sphaerotheca macularis (on Humulus lupulus), Uncinula clandestina (on Ulmus minor), Uromyces rumicis (on Rumex sanguineus), Ustilago vaillantii (on Scilla bithynica).
- Animals: Vertebrates – Picus canus, Ciconia nigra, Milvus migrans, Buteo buteo, Pernis apivorus, Ficedula semitorquata.
Distribution in Bulgaria. Danubian Plain, and Ludogorie region, along the lower parts of the valleys of larger rivers in East Bulgaria – Kamchia, Batova, Ropotamo, Dyavolska, Veleka, and Rezovska rivers. Their distribution is more limited in the middle parts of the valleys of Toundzha and Maritsa rivers.
Conservation importance. The mixed lowland and riparian forests and longoses have fragmented distributions and cover about 5000 ha in total. More than 20 species of conservation value occur in them, among which most frequent are Fritillaria pontica, F. stribrnyi, Galium bulgaricum, Pastinaca umbrosa, Primula vulgaris subsp. sibthorpii,Scilla bithynica, Sison amomum. Fungi of conservation importance also occur: Agaricus bohusii, Clathrus ruber, Hymenogaster verrucosus, Lenzites warnieri, Phellinus pilatii, and Ptychoverpa bochemica.
Threats. Replacement of the natural habitat by intensive plantations of hybrid poplars and by agricultural land; unregulated logging and felling; clearing of the tree vegetation in the river valleys; invasive species. Hydro-ameliorative activities: construction of dikes, draining, redirection of river beds, have caused changes in the water regime and deterioration of the conditions in the alluvial forests. Natural threat is the erosion along the Danube, constant changes in the bank and destruction of islands and originating of new ones. The climatic changes cause floods and consequent droughts that are also a threat for the willow-poplar forests. The natural resources of the medicinal plant Leucojum aestivum are a subject to over-exploitation and have been significantly reduced. Construction activities, building of communication facilities and frequent visits for different purposes also are among the threats for this habitat.
Conservation measures taken. The habitat is included in Annex №1 of the national Biodiversity Act. Being of high conservation value these forests have been included in different protected areas: Kamchia, Ropotamo, Gorna Topchiya Strict Nature Reserves; Dolna Topchiya, Baltata, Balabana Managed Nature Reserves; Strandzha, Zlatni Pyasatsi Nature Parks; Ustieto na reka Veleka, Silistar, Ormana, Kalinata Protected Sites, as well as in sites of the European Ecological Network NATURA 2000 in Bulgaria.
Conservation measures needed. Prohibition of: felling and logging, “clearing” of the river valleys from the natural riverside forests and grazing. Restoration of destroyed riparian woodlands; mapping and monitoring of the best preserved and most vulnerable habitats and improvement of the forest protection.
References. Ganchev 1965; Kochev 1976; Pavlov & Dimitrov 2002; Penev et al. 1969; Penev 1981; Radkov & Minkov 1963; Rousakova & Tzonev 2003; Soo 1957; Stefanov 1924; Stoyanov 1928; Tsanov 1992.
Authors: Marius Dimitrov, Rossen Tzonev
