Abstract

Mediterranean forests including Tunisian pine species are threatened by the rising of temperature and decreasing of precipitation. The impact of the increase of aridity differs across species depending on their stomatal and hydraulic responses. In this paper, three pine species: P. halepensis, P. brutia and P. canariensis growing in three different climatic zones: humid, sub-humid and semi-arid, were studied to detect their different responses to drought and guide their selection for reforestation program. Measurements carried out are hydraulic conductivity at point P₅₀, specific conductivity (Ks), midday stem water potential and hydraulic safety margins. Results showed that during summer, vulnerability to embolism, estimated by water potential inducing 50% loss of xylem hydraulic conductivity (P₅₀), is strongly associated with the capacity for drought resistance. Pinus halepensis (P₅₀ = -4.19 MPa) was found to be more resistant to drought than P. brutia and P. canariensis in the semi-arid climate, whereas P. brutia tolerated the humid climate (P₅₀ = -3.7 MPa) and P. canariensis seems more adapted to the sub-humid climate (P₅₀ = -4.08 MPa). Hydraulic safety margins confirmed the conservative behavior of pine species to avoid drought and for maintaining relatively high water potential in dry conditions. These findings help to assess the impact of mid-summer water deficit on pine species in the context of climate change and to select among these species the most resistant for future reforestation programs.

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