Upstream of the lagoons, there used to stretch a vast forest of oak, hornbeam, elm and ash trees that took on the current range of flora about 1000 BC. Over the millennia, humans gradually reduced this great lowland forest, but in 1816 but there were still no less than 4965 hectares of forest, although at present there are less than 600 hectares. The largest woods are upstream of the lagoon of Marano in the municipalities of the Muzzana del Turgnano and Carlino. The ecological importance of these forests lies in their being the best preserved examples of the potential and relatively stable vegetation of the densely populated plains of the eastern Po basin.