The Paulis

The paulis are shallow depressions that are able to collect and store rainwater throughout the year. There are about thirty main ones, covering an area of 120 hectares, which is more or less 2 percent of the entire territory of the Giara. They are spread throughout the plateau, especially near the reliefs of Monte Zepparedda (609 meters) and Zeppara Manna (580 meters). The largest paulis, located in Tuili e Genoni, are both called Pauli Maiori. Local tradition has assigned names to only twenty of the thirty paulis on the plateau. Among these, Pauli Tramatzu, Pauli Cerrobica, Pauli Perdosu, and Pauli s'Ala de Mengianu deserve special mention.

The water temperature in the different ponds varies seasonally from zero to more than thirty degrees Celcius. The salinity, however, remains constant due to evaporation. The bottom has different characteristics, as it can be stony or slimy.

These environments are critically important to the lives of many plant and animal species. Together they are considered to be oligotrophic bodies of water, despite the lack of depth and the presence of organic substances due to grazing. Because of their characteristics and the significance of the species that live there, they can be considered natural environments of great importance. In fact, they are listed as priority habitat 3170 * - "Mediterranean temporary ponds" in the Natura 2000 network.

 

Horses and Riders

In spring, the extraordinary common water-crowfoot covers these bodies of water, coloring everything white. The famous Giara horses (Equus caballus giarae) are assiduous eaters of these plants, so it is very common to see them crossing the wetlands of the plateau in the tranquility of the pasture. The fauna of the paulis, besides the horses, includes several species of resident and migratory birds, some of which carry out regular trips to the southern regions of the island. There are some rare and protected species, such as the black-winged stilt (Himantopus himantopus), and some species of the genus Anas, such as the northern shoveler (Anas clypeata), the mallard (Anas platyrhynchos), the garganey (Anas querquedula), the little grebe (Tachybaptus ruficollis) and the common moorhen (Gallinula chloropus). Some species are occasional, whereas others have been observed only a couple of times in the waters of Pauli Maiore of Tuili, including the pink flamingo (Phoenicopterus roseus) and the white stork (Ciconia ciconia). It is worth mentioning the presence of the western marsh harrier (Circus aeruginosus) in the whole area. It is well-suited for wetlands of reduced extension that are rich in marsh vegetation.

Among amphibians, next to the European green toad (Bufo viridis) and Sardinian tree frog (Hyla sarda) is the Tyrrhenian painted frog (Discoglossus sardus), included in Annex II of the Habitats Directive. Among reptiles, it is important to remember the European pond turtle (Emys orbicularis). The microfauna is diverse and well-differentiated, as it characterized by the presence of several organisms, including a very large collection of insects in the larval stage (water beetles, Lepidoptera, Odonata, Trichoptera, Diptera, and Ephemeroptera) as well as Hirudinea and nematodes.

 

"Living fossils"

The environmental characteristics of the wetlands of the plateau vary during the year, reaching complete dryness during the summer, when the ponds almost disappear. Besides the animal species previously mentioned, which are able to move away from paulis in the hottest period, there are some sedentary species that are able to adapt to the dryness in different ways, such as those capable of developing small cysts and produce eggs that tolerate the summer heat.

Among the crustaceans that inhabit the muddy bottoms of the paulis, it is worth mentioning the presence of two archaic notostracans, two small "living fossils" that have remained unchanged for 200 million years, whose eggs survive for decades: Triops cancriformis and Lepidurus apus lubbocki. This latter is no larger than two centimeters and is currently extinct in Continental Europe and is rare in the Mediterranean. It has an archaic appearance that is characterized by a shield-shaped shell and a forked tail. It feeds on organic waste and transforms into a skilled predator that is capable of capturing even a few tadpoles when it is necessary.              

The numerous copepods and ostracods that live in this environment usually feed on plant debris and decomposing animals. Other organisms survive during the warmer months, taking advantage of small spaces under rocks or in soil cracks (these are small molluscs and turbellarians). Finally Hirudo medicinalis, being a parasite species, can be easily observed when horses, cattle and other wildlife frequent the ponds.

 

The Paulis Throughout the Year

The appearance of paulis varies greatly with the seasons. On the bottom of the various basaltic ponds, covered with pebbles, clay, silt, and organic debris, different plants are rooted and larvae and eggs from many species find shelter.

In the spring, the paulis appear almost totally covered by the white flowers of the common water-crowfoot (Ranunculus aquatilis), which is spotted with loose-flowered orchids (Orchis laxiflora). Eryngium corniculatum is very rare, and it shows its long leaves that emerge from the water during this period.

As the ponds dry up due to the heat, the white buttercups give way to the pink Baldellia ranuncoloides, whose sweet smell fills up the entire plateau. The intense summer heat gives the delicate tinge of the Elatine hydropiper to the few areas that still retain a layer of water. Soon after, most of the ponds dry up, revealing the characteristics of the depths. Paulis Perdosu and Oromëo show a stony surface of lunar aspect; Pauli Maiori, characterized by a silty bottom, shows large tracts full of cracks  punctuated by Eryngium corniculatum that, with its leaves and thorny bracts, produces small inflorescences. With the arrival of the drought, the wildlife increases in number by adding the countless insects that have now abandoned the larval stage.

In the surface of the watering holes that have survived, you can see some Heteroptera, such as Notonecta glauca, Hydrometra stagnorum, and Gerris lacustris. Also, some voracious predators, such as Dytiscus circumflexus, which hunts insects and Hydrous sp., which feeds on decomposing material. In the dry parts of the paulis, which are seemingly lifeless, there are spores, plant seeds, and insect larvae and eggs from crustaceans, including those of Lepidurus apus lubboki.

The autumn rains bring the water back to the ponds. The dark red of the tamarisk, covered by small inflorescences, frame the reflections of Pauli Tramatzu. Even with the rigidity of winter and the thin layer of ice that covers the surface of the water, you will see these environments protect the most diverse species that find the suitable temperatures for the germination of their seeds and the beginning of a new cycle of life in these still waters.