Boundaries

This ecoregion encompasses the river drainages of northern Italy, including tributaries of the Po that extend into France and southern Switzerland, the Isonzo River that extends into western Slovenia, and other Western Adriatic coastal rivers as far south as the San Benedetto del Tronto. These rivers all drain into the Adriatic Sea from the Western Alps to the Julian Alps in the north, as well as the northern and central Apennines. Bordering ecoregions include the Cantabric Coast-Languedoc [403] to the west, Central and Western Europe [404] and Upper Danube [417] to the north, Dniester-Lower Danube [418] and Dalmatia [419] to the northeast, and Italian Peninsula and its islands [416] to the south-southwest.

Topography

This ecoregion has an extremely varied topography represented by alluvial plains and tall mountains. The Po Valley (or Padanian Plain) separates the Apennines in the south from the high, rugged peaks and deep, scoured valleys of the Alps. The highest peak is Mont Blanc, rising 4810 m asl on the French-Italian border (Hijmans et al. 2004). Not only is it the highest mountain in the ecoregion, but it is the highest mountain in the Alps and in Western Europe. Other high peaks in the ecoregion above 4000 m asl include Mont Blanc de Courmayeur (4748 m), also on the Mont Blanc massif, and Monta Rosa (4634 m), Nordend (4609 m),  Dufourspitze (4634 m), and Ostspitze (4632 m) on the Monta Rosa massif. The Alps were formed during the Alpine orogeny, and include outcrops of crystalline basement as well as sedimentary rocks. Forming the backbone along the length of the Italian Peninsula are the Apennine Mountains, which are younger and shallower than the Alps, but still steep with rugged relief. They are composed of mainly sedimentary Mesozoic-Tertiary rocks, including limestone, dolomite, marl, schist-marl, and sandstone (Daglioni & Flores 1997; WWF 2001).

Freshwater habitats

The Gulf of Venice Drainages ecoregion is notable in that it contains a majority of Italy’s freshwater. Most of the rivers in northern Italy are fed by glacial streams with relatively high discharge due to high rainfall and runoff from Alpine glaciers and snowfields. Covering nearly a quarter of the Italian mainland, the Po River basin is the largest at roughly 74,000 km². Originating from Mount Monviso at 2022 m asl, this river flows east more than 650 km to the Adriatic Sea with a mean annual flow of roughly 80 km³. It contains three sections: namely an Alpine region with crystalline basement, and Apennine region with sedimentary origins and high clay content, and a central alluvial region with thick sedimentation. It has a mountain character in its upper reaches; transitioning to meanders and islands in its middle reaches; and then is characterized by oxbows, side channels, meanders, islands, and braided sections in its lower reaches. It receives tributaries from both the Alps and Apennines. Alpine tributaries have a more regular flow regime, whereas Apennine tributaries flood in spring and autumn, resulting in flooding along the Po (Gumiero et al. 2009). The largest lakes in the ecoregion – Garda, Maggiore, Como, and Iseo – are alpine glacial lakes and moraine systems within the Po basin. Its delta represents the largest wetland area in Italy and comprises an extensive complex of lagoons, such as the Valli di Comacchio and Po Delta (Wetlands International 2005).

The second longest river in Italy is the Adige. Originating in the West-Central Alps, it flows 410 km to the Adriatic Sea through valleys, gorges, canyons, and plains. Much of its length flows through the Alps where its headwaters are fed by snowmelt, rain, and glaciers. Once reaching the Po Valley it runs nearly parallel to the Po River. Mean annual discharge historically (prior to the construction of reservoirs in the 1950s) was 252 and 205 m³/s (Gumiero et al. 2009).

Compared to most Italian rivers, the Tagliamento is relatively pristine. Most of this basin lies in the Alps with a mean elevation of nearly 1000 m asl. Its steep slopes, along with torrential rains and snowmelt, contribute to flooding and large sediment loads. Its mean annual discharge in the upper basin is 90 m³/s with peaks in autumn and spring. Downstream of Pinzano the river flows through an alluvial aquifer and decreases its surface flow substantially (Gumiero et al. 2009).

Terrestrial habitats

The Gulf of Venice Drainages encompasses four terrestrial ecoregions, including (from north to south): Alps conifer and mixed forests [PA0501], Po Basin mixed forests [PA0432], Italian sclerophyllous and semideciduous forests [PA1211] and Apennine deciduous montane forests [PA0401] (ECB/NTB 2002; WWF 2001).

Common species of the Alps conifer and mixed forests include pedunculate oak (Quercus robur), sessile oak (Q. petraea), downy oak (Q. pubescens), and Scots pine (Pinus sylvestris) at elevations between 700-900 m asl; beech (Fagus sylvatica), silver fir (Abies alba), and sycamore (Acer pseudoplatanus) in the montane zone between 1300-1600 asl; Norway spruce (Picea abies), dwarf mountain pine (Pinus mugo), and ericaceous shrubs in the sub-alpine zone; and dwarf ericaceous shrubs, juniper scrub (Juniperus communis), and relict species in the alpine zone (WWF & IUCN 1994).  The southern alpine slopes contain a diversity of species common to Central Europe as well as the Mediterranean montane zone (Gumiero et al. 2009).

Although little remains, the Po Basin was once covered with mixed deciduous oaks forests with species such as pedunculate oak, turkey oak (Q. cerris), common hornbeam (Carpinus betulus), and field elm (Ulmus minor). Extensive areas of riparian forests were also once present with characteristic species such as Raywood ash (Fraxinus oxycarpa), white willow (Salix alba), and black alder (Alnus glutinosa).

Montane areas of the northern Apennines share a number of species with the southern slopes of the Alps (Gumiero et al. 2009). Common species include holm oak (Q. ilex), cork oak (Q. suber), downy oak, manna ash (F. ornus), hop hornbeam (Ostrya carpinifolia), and European nettle (Celtis australis) at low elevations; turkey oak, downy oak, Italian oak (Q. frainetto), and European chestnut (Castanea sativa) at medium elevations; and mixed deciduous forests dominated by beech, dwarf mountain pine, and endemics such as Androsace mathildae, Ranunculus magellensis, Aquilegia magellensis, and Soldanella minima samnitica at higher elevations (WWF 2001).

Description of endemic fishes

The ecoregion contains high endemism, with around a third of the species being strictly endemic to the Po and other drainages. Cyprinids represent around half of the endemics with species such as the Insubrian barbel (Barbus caninus), savetta (Chondrostoma soetta), Italian gudgeon (Gobio benacensis), and triotto (Rutilus aula). There are also endemic salmonids, including the carpione (Salmo carpio) and Northern Italian brook trout (S. cenerinus) (Kottelat & Freyhof 2007). Many of these endemics are threatened, such as the endangered Insubrian barbel, savetta, and Italian gudgeon; and the critically endangered carpione (Smith & Darwall 2006).

Other noteworthy fishes

The ecoregion notably contains both landlocked and anadromous shads. The agone (Alosa agone), is restricted to lakes Maggiore, Lugano, Como, Iseo, and Garda in northern Italy, whereas the anadromous Twaite shad (Alosa fallax) is widespread throughout the Adriatic and Mediterranean seas. There is also the anadromous North African shad (A. algeriensis), which is found in Western Sardinia. Questions regarding their systematics are still ongoing, but for now are considered to be separate species (Kottelat & Freyhof 2007).

Ecological phenomena

The Po drainage represents the westernmost extent of the anadromous Adriatic sturgeon (Acipenser naccarii). Critically endangered, this species is now rare in the wild, with only one naturally spawning population occurring at the confluence of the Po and Ticino rivers (Kottelat & Freyhof 2007).

Justification for delineation

Southern European ecoregions were delineated based on a bottom-up approach employing both published and unpublished field data and expert assessment (Abell et al. 2008). This includes information based on Bianco’s (1986; 1995) divisions of Italy.

Level of taxonomic exploration

Good