Floodplain Forests Along the Lower Danube

Transylv. Rev. Syst. Ecol. Res. 8, (2009), "The Wetlands Diversity" 113 FLOODPLAIN FORESTS ALONG THE LOWER DANUBE Erika SCHNEIDER-BINDER * * Karlsruhe University, Institute for Waters and River Basin Management, Division World Wide Fund - Institute for Floodplain Ecology, Josef Street 1, Rastatt, Germany, D - 76437, [email protected] KEYWORDS: Danube, floodplain forests, black and white poplar gallery forests, poplar-elm forests, elm-oak forests relict habitat types. ABSTRACT The present paper presents the results of the studies conducted in the floodplain forests along the Lower Danube. Emphasis was prevalently put on near-natural black poplar and white poplar forests, poplar-elm forests as well as the few remaining oak-elm floodplain forests that have been studied on various sections along the Romanian-Bulgarian Danube. They are allocated to the Salici-Populetum, Fraxino-Ulmetum and Ulmo-Quercetum roboris associations. Floodplain forests are threatened all over Europe and are listed in Appendix I of the Directive on the Conservation of natural habitats and of wild fauna and flora under 91E0 *Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae), presented more on smaller water courses, 91F0 Riparian mixed forests of Quercus robur, Ulmus laevis and Ulmus minor, Fraxinus excelsior or Fraxinus angustifolia, 92A0 Salix alba and Populus alba galleries. Further studied communities are tamarisk bushes that are listed under 92D0 Southern riparian galleries and thickets (Nerio-Tamaricetea and Securinegion tinctoriae), occurring frequently together with the White poplar gallery forest. The curtains of wild wine (Vitis sylvestris) and on the eastern section of the Lower Danube also of the silkvine Periploca graeca and Cynanchum acutum give them a tropical touch. ZUSAMMENFASSUNG: Die Auwälder entlang der unteren Donau. In vorliegender Arbeit werden die Ergebnisse der Untersuchungen in Auenwäldern entlang der Unteren Donau vorgestellt. Dabei geht es vorwiegend um die naturnahen Schwarz- Pappel und Silberpappel-Wälder, um die Pappel-Ulmenwälder sowie um die Eichen-Ulmen- Auenwälder. Diese wurden in mehreren Abschnitten entlang der rumänisch-bulgarischen Donaustrecke untersucht. Sie sind den Assoziationen Salici-Populetum, Fraxino-Ulmetum und Ulmo-Quercetum roboris zugeordnet. Die europaweit gefährdeten Auenwälder sind in Anhang I der FFH Richtlinie unter 91 E0 *Auenwälder mit Alnus glutinosa und Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae), die mehr an kleineren Gewässerläufen vorkommen, 91 F0 Eichen-Ulmen-Eschen - Auenwälder (Quercus robur, Ulmus laevis, Ulmus minor, Fraxinus excelsior oder Fraxinus angustifolia), 92D0 Galeriewälder mit Salix alba und Populus alba eingegliedert. Hinzu kommen Tamariskenbüsche, die zu Lebensraumtyp 92D0 Südliche Galeriewälder und Tamariskengebüsche (Nerio-Tamaricetea und Securinegion tinctoriae) gehören. Die Schleier von Wilder Weinrebe (Vitis sylvestris) und im östlichen Abschnitt der Unteren Donau auch Griechischer Liane (Periploca graeca) sowie zum Teil Cynanchum acutum verleihen den Auenwäldern einen tropisch anmutenden Charakter. 114 E. Schneider-Binder – Floodplain forests along the Lower Danube (113 ~ 136) REZUMAT: Pădurile de luncă, de-a lungul Dunării inferioare. Lucrarea prezintă rezultatele cercetărilor efectuate în pădurile de luncă de-a lungul Dunării inferioare. Studiul se referă, în primul rând, la păduri cvasi naturale de plop negru şi plop alb, păduri de tranziţie de plop alb, plop negru şi ulm, precum şi la suprafeţele mici rămase din pădurile de stejar şi ulm, care au fost studiate în diferite locuri ale Dunării inferioare, în sectorul de frontieră între Bulgaria şi România. Fitocenozele, cercetate, au fost încadrate în asociaţiile Salici-Populetum, Fraxino-Ulmetum şi Ulmo-Quercetum roboris. Pădurile de luncă, periclitate la scară europeană, sunt listate în anexa I a Directivei FFH sub numerele 91E0* Păduri aluviale cu Alnus glutinosa şi Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae) prezente mai mult pe râurile interioare, 91F0 Păduri mixte ripariene cu Quercus robur, Ulmus laevis şi Ulmus minor, Fraxinus excelsior sau Fraxinus angustifolia de-a lungul râurilor şi fluviilor, 92A0 Galerii cu Salix alba şi Populus alba. Deseori în strânsă relaţie cu galeriile de plop alb, apar tufărişuri de cătină roşie Tamarix ramossisima cuprinse în tipul de habitat 92D0, galerii ripariene şi tufărişuri sudice (Nerio-Tamaricetea şi Segurinetea). Perdelele de viţă sălbatică în sectorul estic al Dunării inferioare şi de liană grecească (Periploca graeca) şi Cynanchum acutum oferă acestor păduri o nuanţă tropicală. INTRODUCTION Man’s intervention on European rivers, and thus on the Danube River as well, that took place in the nearer and farer past resulted in a dramatic reduction of floodplain forests. On the one hand the surfaces became smaller, on the other hand the remaining floodplain forests have been dramatically altered as for their structure and species composition as a result of interventions for sylvicultural purposes. From an ecological point of view the remainders of near-natural floodplain forests are thus of very great importance. There are on the one hand the softwood floodplain forests, on the other hand there are those of the hardwood floodplain and those showing transition characteristics. Depending on their ecological significance they attract special attention as from a point of view of nature conservation. Accordant to their importance the floodplain forests have been classified as habitats of pan-European importance and as such recorded in Appendix I of the Directive on the Conservation of natural habitats and of wild fauna and flora 92/43/CEE. Climatic and phytogeographic aspects of floodplain vegetation along the Danube River. The Danube River and its floodplains shows a considerable West-Southeast extension and thus its life communities and vegetation composition is not only defined by the ecologically determining factors such as the hydrological and morphological dynamics, but also by the continentally gradients of the climate. This becomes obvious from the comparison of the floodplain vegetation occurring along the varying sections of the Danube River. Whereas the influence of the sub continental-central European climate prevails on the Upper Danube (abundant summer precipitations and moderately cold winters), the pannonian lowlands already show a continental influence (moderately poor winter precipitations and relatively frequent years with dry late summers). In the southern regions the central European- submediterranean climate affects the vegetation of this area. In the easternmost Danube region, the large floodplain on the Lower Danube, as well as in the Danube Delta, the impact of a typically continental climate becomes apparent (summer aridity, frequent frosty winters with little snow) (see also Walter and Lieth, 1964; Horvat, Glavac and Ellenberg, 1974; Schneider, 2003). Transylv. Rev. Syst. Ecol. Res. 8, (2009), "The Wetlands Diversity" 115 The influence of these above mentioned factors on the azonal floodplain vegetation results in a very concise classification of the Danube floodplains. This classification differentiates, with a growing continentally in the eastward direction, by the occurrence of section-specific species. These influences reflect increasingly in the species composition of hardwood floodplain forests and may be anticipated from the occurrence of geographic differential species. The sometimes still gallery-like softwood floodplain stands, however, are more azonal. The alpine-prealpine Upper Danube (in Bade-Wurttemberg/Germany) is characterized by the occurrence of alpine species in the river-attending vegetation that is frequently reduced to a small fringe. The central European moderately continental upper Danube area is mainly characterized by European respectively central European species of the colline level. Very characteristic of the whole Upper Danube’s pre-alpine area are also numerous alpine plants that have been washed ashore in the lowlands by the Danube’s tributaries. These are partly species of dynamic pioneer stands with large grain sized sediments, among others Salix elaeagnos, German Tamarisk (Myricaria germanica) and grey alder (Alnus incana). Moreover, the hardwood floodplain forests comprise a number of alpine calcareous beech forests species (Schneider, 2003). The pannonian section is much more continental and is characterized by the occurrence of pontic-pannonian and continental but also submediterranean, thermophilic species. These do already occur partly in the Danube floodplains east of Vienna (Margl, 1971; Schneider, 2003b). In the Southern area of the pannonian lowlands thermophilic species such as Black bryonia (Tamus communis), Butcher’s broom (Ruscus aculeatus) and Carpesium abrotanoides point out a submediterranean-illyric influence (Pócs, 1991). This influence also proceeds in the breach valley area of the Iron Gate („Clisura Dunării”), where a submediterranean-illyric characterized rock vegetation of Orno-Cotinetalia dominates. This thermophilic, submediterranean but also Balkan-Moesian characterized rock vegetation occurs over long stretches along the right bank of the Lower Danube, where the hills of the Bulgarian chalkstone table are steeply sloping down to the river. Downstream the Iron Gate up to around the mouth of the Olt River in the Danube ensues a submediterranean and increasingly Balkan-Moesian section (Borza

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