Long-term Effects of CO2-increase and Climate Change on European Forests (LTEEF). Project final report

Water availability in Mediterranean regions is likely to be altered by the increase in atmospheric carbon dioxide and related climate changes. Predictions have been made that the water resource may become less available as the carbon resource becomes more available. A proper understanding of the response mechanisms of trees to water shortage is a prerequisite for making predictions on the impact of climate change on the Mediterranean forests. Water availability affects trees in several ways; for instance, combined low soil water content and high vapour pressure deficits can induce xylem embolism. The hypothesis has been tested that even under severe drought conditions no runaway xylem embolism and irreversible reduction of plant hydraulic conductance may occur in Mediterranean conifer trees, due to the control of transpiration by the adjustment of stomatal aperture or carbon allocation. Validation or falsification of this hypothesis is relevant to improve process-based LTEEF models.