Location and General Description
The 115,000 km2 Po Basin slices an arc between 43-46° north latitude and 7-15° east longitude. It includes northern Italy’s Lombardy, Po River, and Veneto plains, as well as the northern Adriatic coastland. The Po Basin is surrounded by the foothills of the Southern Alps to the west and north, and by the Northern Apennine Mountains to the south. The Po Basin experiences a Mediterranean climate in the south, and a continental climate in the north (Alpine climate). This region is cooler than the Italian Peninsula lowlands in winter, and it can be quite warm during summer, with extremely high air humidity and persistant dense fog. Total annual rainfall ranges from 500 to 1,000 mm.
A few remaining small pockets of natural vegetation help us understand what the Po Basin vegetation would have looked like before very intensive human intervention. Mixed deciduous oak forests of Quercus robur, Q. cerris, Carpinus betulus, Ulmus minor, and Fraxinus ornus once occurred throughout the ecoregion. Riparian forests occupied the periodically flooded valleys of less than 100 m of elevation, and were composed of Fraxinus oxycarpa, Salix alba, Alnus glutinosa, Ulmus minor, Populus alba, P. nigra, and Quercus robur. Peat bogs and swamps appear frequently within this vegetation type. Conifer and broadleaf mixed forests, located on the moraine hills, are characterized by Pinus sylvestris, Castanea sativa, Betula pendula, and Quercus robur. Invasive Robinia pseudoacacia woodlands are widely spread. Heather (Calluna vulgaris) communities are found on outcrops and rocky slopes. Relict Mediterranean sclerophyllous (Quercus ilex) and dry conifer (Pinus pinea) woodlands appear in the coastal sand dunes and flatland in the Po delta, near Ravenna. Brackish lagoons are found in the coastal regions.
The greatest biodiversity value of the Po Basin lies in and around its freshwater ecosystems. These systems have a high level of biodiversity, and support many plant species threatened in Italy, including Leucojum aestivum, Nymphaea alba, several Orchidaceae spp., Thelypteris palustris, Salvinia natans, Sagittaria sagittifolia, Utricularia australis, Bassia hirsuta, Halocnemum strobilaceum, Limonium bellidifolium, and Plantago cornuti.
The ecoregion’s wetlands are very important breeding, resting and feeding areas for many bird species. They serve as the most important heron breeding area in Italy for squacco heron (Ardeola ralloides), black-crowned night-heron (Nycticorax nycticorax), and little egret (Egretta garzetta) (700 – 1,000 pairs). The Po Basin contains the only nesting site in Italy of pygmy cormorant (Phalacrocorax pygmaeus). The globally threatened ferruginous duck (Aythya nyroca) is also a resident of the basin. There are regularly more than 20,000 waterbirds present, including populations of Ciconiiformes, Anatidae, Accipitriformes, Charadriidae, and Sternidae. Several endemic species of fish are present, and the valleys function as nurseries for many species, including some that are rare and/or threatened.
Since Medieval times, the natural vegetation of the Po Basin has been intensively transformed into agricultural land. Currently, 90% of its surface is planted with rice, cereals, grass, fruit trees, and poplar plantations. The region is also one of the most industrialised in Europe, and includes many large towns, industries, and a very dense road network.
Types and Severity of Threats
The few remaining wilderness areas are scattered small riparian woodlands and wetlands. Natural forests are highly disturbed by the invasion of the exotic black locust (Robinia pseudoacia). Primary threats to the ecoregion are related to a number of issues. Water, soil, and air pollution is a problem, as is water shortage and the drying up of wetlands due to intense irrigation and urbanisation nearby. Invasive species threaten native flora and fauna. Introduced animal species including nutria (Myocastor coypus), stone moroko fish (Pseudorasbora parva), and wels catfish (Siluris glanis) are having negative impacts. This problem is compounded by the increasing biomass of the lotus, Nelumbo nucifera, a fast-growing, aggressive exotic plant, which, in addition to hampering the flow of water through river channels, is also suffocating the original native flora. The effort to halt the spread of Nelumbo nucifera is now showing excellent results. The Robinia invasion of forested land is also creating great problems in the remaining natural forests. Poaching and hunting pose a serious threat for Anatidae (waterfowl) species. Another problem is the nearly complete suspension of the traditional cutting and collecting of reeds.
Justification of Ecoregion Delineation
This ecoregion is equivalent to the DMEER unit of the same name. It consists of the mixed oak-hornbeam forests as well as flood-plain vegetation of the Po Basin in Italy (Bohn et al. 2000).
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Prepared by: Pedro Regato
Reviewed by: Leann Trowbridge