Water use of young maritime pine and Eucalyptus stands in response to climatic drying in south-western France

Abstract

Background: There is increasing interest in developing eucalypt stands in France for biomass energy, but the water requirements of eucalypt coppice are largely unknown. Aims: We assessed the water use and growth of two 5-year-old managed forest stands: an indigenous maritime pine stand and an introduced eucalypt stand. Methods: We used a combination of meteorological, sap flow, soil and biomass measurements, between September 2009 and July 2011. Results: The stand structure was the main driver of both water use and its partitioning between water balance components in each site. The evapotranspiration was high in the eucalypt stand, with a significant contribution of tree transpiration due to high leaf area index of the tree canopy. Under well-watered conditions, both species exhibited a similar stomatal behaviour in relation to vapour pressure deficit and, with high biomass production, the two stands presented a maximal water use efficiency in respect to their local environments and constraints. However, they experienced significant sensitivity to successive early spring and summer droughts. The unexpected prolonged soil water deficit in the eucalypt stand, induced by high water consumption and insufficient water supply, directly impacted leaf shedding and stem secondary growth. In contrast, the pines appeared conservative with respect to soil water deficits and maintained secondary growth.