Cycles biogéochimiques et bilan d´eau dans les forets caducifoliées de l´Ouest de l´Espagne (Sierra de Gata, Province de Salamanque)

Biogeochemical cycles of ten elements, water balance, and dynamics of the soil water content in four oak (Q. pyrenaica) forest, selected according to a rainfall transect in the "Sierra de Gata" mountains (Western Spain), have been studied. So, four permanent experimental plots are running on, and monitoring of bioclimatic parameters, and other data about production, growth, litter decomposition, etc, are registered. Results show that production and decomposition are independent from the annual pluviometry. Concerning the soil humidity, is observed the existence of two critical phases: autumn watering and summer dryness: during the transpiration values decrease from moderate to low, showing that in all the forest the summer dryness is a limitant factor, despite the annual total rainfall. Growth and production is higher in the forest with the lowest rainfall.