The Climate of the Borna Maggiore di Pugnetto Cave (Lanzo Valley, Western Italian Alps)

We have studied the internal climate of the Borna Maggiore di Pugnetto (Western Alps), starting from the survey of geological structure, of geomorphology and of vertical distance between cave floor and topographic surface. Then we studied the variations in temperature in the soil and in the air; the distribution of temperature and humidity in soil and air on four days that representing the four seasons. According the geomorphic data, the Borna is a through cave (hydro-geological tunnel). Three major heat sources regulate the thermal dynamics of the cave. In a branch enters water relatively warm, which is the main responsible for the distribution of temperature in this part of the cave. The entrance (at the opposite side of the cave) puts in communication the cave with the outer atmosphere, causing temperature changes, more and more attenuat ed inwards. Thermal imbalance between cave's ends probably causes the air circulation, which tends to homogenize the temperature of the air and soil, especially in the innermost part of the cave. The drip water is the third heat source: after the rains, causes sudden changes in temperature since October until June, after the starting of period of water surplus. The thermal dynamic of the cave makes almost constant temperatures, and divides the inner atmosphere in thermic zones, such as cold depressions, are as with constantly mild temperature, and traps to the warm air. This, combined with the constant temperature difference between air, walls and floor of the cave, creates many adjacent microhabitats. This factor, together at the proximity to glaciers in past, explains the great biodiversity of the cave.