|DRY STONE WALLS
Definition characters description and diffusion
They dry stone walls impound the moisture and help supply the soil with water. The different thermic inertia with the atmosphere creates colder surfaces which originate condensation. The walls intercept both the wind and the humidity. The interstices between the blocks and the porosities of the rock impound water. The shade protects from evaporation. The heaps of stones stop the demolishment of the soils and foster the production of humus. They preserve the hydromorphic qualities of the soil by acting as thermoregulators and controlling the humidity in both arid and deeply cold climate conditions. Thus, they help to supply the soil with liquid water that is used by the plants and prevent the water from freezing.
General characters description and diffusion
Most of the dry stone constructions spread throughout the Apulian barren lands, where mounds of porous stones absorbs the night frost and replenish the soil with moisture, can be considered as water producers (Cantelli, 1994). As a matter of fact, the roots of the ancient olive trees all stretch towards the dry stone walls which are typical of the agricultural landscapes. Still now, olive trees wholly bounded by dry stone walls exist. It is meaningful that in the most imposing structures, the parieti, the rows of stones that close the upper part of the two faces of the walls are arranged with slabs leaning towards the inner part in order to allow the frost to drop down the mound of stones filling the interior. The fact that this technique has spread over northern Europe, northern Scotland, Ireland, and the Orkney Islands, would make one think of a spread linked to cultural reasons, as a heritage of the prehistoric megalithic culture and of pastoral practices. However, it is necessary to consider that in cold climate conditions, the walls act as thermoregulators and provide the plants with an adequate water supply. In the region of the Burren, in Ireland, in spite of a humid and rainy climate, the pastoral needs and the karsification have caused the spread of pools and of the rainwater catchment systems. Some of them date back to the age of the dolmens, the cromlecks and the prehistoric fences present in the area. Certain devices that are still in use could help to explain how the heaps of limestone rock called specchie typical of the Apulian region, in the south of Italy, work. Heaps of oblong stones very similar to the specchie have their tops covered with palster for the harvesting of rainwater that pours down into side tanks. For want of rainfall the stone barrow itself attracts the moisture and provides the water supply. In Sardinia and in the Isle of Ibiza there are systems of fields surrounded by dry stone walls called tanka which is a term deriving from an ancient Mediterranean toponym. In Yemen, there are structures such as marbid which are low dry stone walls producing moisture which is harvested on the flat surface they surround.
Advantages and sustainability
Dry stone walls offer many benefits including the protection of the soils, the interception of wind and humidity, the supplying of the soil with water through condensation, and the supplying of shade from the sun, the fostering of the production of humus, and finally the regulation of humidity.