The central part of the Po has basically an artificial connotation, whose runoff regime is influenced by the hydrological, geomorphological, climatological conditions, but also and above all by the hydraulic and soil defense systems that have been operated along its course and its tributaries. The Po river belt is an area in which geomorphological phenomena (erosion, deposition) characteristic of river dynamism partially persist; this allows the existence of coenosis of relevant naturalistic interest and of a high environmental diversity, where the shore defense works are not very extensive. Such dynamism allows to maintain topographic situations and vegetal and animal coenosis characteristic of intermediate evolution states of the periphery wetlands. These processes are not preserved in a good state of integrity along the entire stretch concerned and, in general, there is a loss of naturalness proceeding from mountain to valley. The central stretch of the Po is still characterized by a considerable biodiversity unfortunately insufficiently protected.
The protected habitats are mostly riparian forest formations, mainly “alluvial forests of Alnus glutinosa and Fraxinus excelsior, mixed riparian forests of large rivers Quercus robur, Ulmus laevis and Ulmus minor, Fraxinus excelsior or Fraxinus angustifolia e gallery-forests of Salix alba e Populus alba, whose state of conservation is “inadequate” or “bad with a continuously worsening trend, as attested by the latest ISPRA Report. Same situation for other typical and more strictly aquatic habitats such as the “Natural eutrophic lakes with Magnopotamion or Hydrocharition type vegetation”, the “Oligotrophic to mestrophic stagnant waters with Littorelletea uniflorae and/or Isoeto-Nanojunctea vegetation” or the “Mediterranean temporary ponds”. The Lombardy Region has identified the entire stretch of the Po as a “priority area for biodiversity” for the importance of its natural heritage which, although in many respects is now residual, is an ecological corridor to be protected and above all restored.
Between Piedmont and Lombardy there is a concentration of the densest nesting populations of species of birds of conservation interest linked to well-preserved shores. Among these are the Common Tern (Sterna hirundo), the Little Tern (Sterna albifrons), the Little Courier (Charadrius dubius) and the Eyeball (Burhinus oedicnemus). These species are also present with lower densities in the remaining stretches of the river floodplain, along with other species of conservation interest, including the Nightjar (Caprimulgus europaeus) and the Montagu’s Harrier (Circus pygargus).
Unfortunately, several of these species, such as the Tern, which until a few decades ago were more widely distributed along the Po, are in continuous decline, threatened by the artificialization of the river that has reduced islands and sandstones and by an often wicked use of the few remaining. Among the few positive signs in recent years there is the recent construction of the fish passage at Isola Serafini, which was a very serious interruption of ecological continuity especially for many species of fish such as the Coby Sturgeon (Acipenser naccarii). However, the morphological variation in the meandering stretch between the confluence of the Adda and the Mincio is not yet overcome. Finally, among the growing threats to the river’s biocenosis there is the spread of many allochthonous species, such as the American shrimp Procambarus clarkii and Orconectes limosus, the bivalve mollusk Anodonta woodiana woodiana and especially many exotic fish species including the now known Silurus glanis.