The bioclimatic originality of Rouvrou's rocky escarpment ('Suisse Normande', France)

摘要

In spite of a cool and moist climate, some rocky escarpments of Suisse Normande present animals and plants which have thermophilous (juniper) and even sub-mediterranean affinities (green lizard, locust of barbary). These bio-indicators materialize very peculiar biotopes. The originality of these florisfic and faunic suite is explained by local factors (topography, exposition, soil, vegetation) which make up for regional climatic conditions and which offer an unexpected biogeographic refuge to thesethermophilous and sub-mediterranean species. This area has the advantage of a continentalization of the atmospheric conditions because of a double shelter effect: sub-regional scale (under the wind of Normandy's hills) and local (valley). These facts induce less moisture and also more sunniness ana warmth. But these better conditions are not enough for thermous and xerous demands, otherwise we would observe a wider distribution of these species which remain very localized and divided. The indispensable"southernalization" of the biotope for the life of these species outside their main distribution area occurs at stational scale, on certain escarpments, thanks to the particularity of the pedo-topographic system: southern exposition, slope, thin and dark soils amplify diurnal dryness and overheating at the soil-air interface. These factors offer thus compatible living conditions for these species outside their main distribution area.