Abstract
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 attenuated 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, areas 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.
Highlights
The objective of this paper is to show the thermal dynamics of Borna Maggiore, an alpine cave considered an excellent example of high biodiversity (S.C.I., i.e. Site of Community Importance)
The losing stream is the part of Cenere River above 880 m a.s.l., which flows parallel at the major set of joints of Fountain Branch
The temperature oscillations of the outside air cannot be the only reason of the variations of the inner climate
Summary
The interdisciplinary project CaveLab “From microclimate to climate change: Caves as laboratories for the study of the effects of temperature on ecosystems and biodiversity” was born in 2013 at the University of Turin, with a team composed of several members of the departments of Life Sciences and Biology of the Systems, Earth Sciences, General Physics, Plant Biology and Analytical Chemistry [10]. The Pugnetto area represents an important spot of hypogean biodiversity in the Western Italian Alps It hosts several natural caves classified by law (European Habitat Directive 43/92, S.C.I. IT 1110048) as “Caves not open to the public” (H 8310), because these caves are exploited as a winter shelter by several species of bats, such as Myotis emarginatus, M. myotis, Rhinolophus ferrumequinum, R. hipposideros [24]. It is worth to mention Dellabeffaella roccai (Insecta, Coleoptera, Cholevidae, Leptodirinae), which is described as the most specialized Leptodirinae in Piedmont [1,13,26], Sphodropsis ghilianii ghilianii (Insecta, Coleoptera, Carabidae, Sphodrini), Alpioniscus feneriensis caprae (Crustacea, Isopoda, Trichonischidae), Dolichopoda ligustica septentrionalis (Insecta, Orthoptera, Rhaphidophoridae) and Troglohyphantes bornensis (Arachnida, Linyphiidae), a cryophilic steno-endemic spider [8,9] Such biodiversity likely reflects the glacial history of the site. For this reason the site should act as a glacial refuge for several cryophilic species [4]
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