The land between Cles and Tuenno is an alternation of hummocks and valleys formed through modelling by rivers and glaciers dating back around 10 to 15 thousand years ago.
This process was interrupted in the 1980s, when the creation of a sports track caused the destruction of some more wetland areas, leading to the institution of the Palù di Tuenno “Biotope”, now a “Nature Reserve” protecting what was defined as the “Last residue of the wetlands on the fluvial-glacial terraces of the mountain plateau, containing interesting plant life”. The influence of man on the morphology of the area, on the vegetation, and on the wetland fractions nevertheless continued over time, with the result that the zone is completely devoid of trees older than the date of institution of the protected area. However, apart obviously from the water itself, the presence of pussy willow (Salix caprea) and other typical wetland trees and bushes, especially reed beds, attracts numerous animal species, especially birds, and the site hosts some particularly rare and protected species. One outstanding case is certainly the little bittern, a small heron with less than 10 breeding pairs in the Province of Trento overall. In spring the males make a call that resembles the distant barking of a dog. In autumn and winter the location is popular with thousands of passerine birds, in particular blackbirds, thrushes, fieldfares, and various species of finches, as an area for passing the night. The ecological term is a “roost”, a dormitory zone where flocks of birds, either resting during migration or overwintering, find protection at night perched among the dense bushes, where they are safe from ground predators like foxes and martens, and diurnal and nocturnal raptors.
