Success in the demographic expansion of Fraxinus excelsior L.

This review examines the ecological traits and ecophysiological characteris tics of the common ash (Fraxinus excelsior L.) that help to explain the cur rent spread of ash communities in Europe. As a consequence of anthropogenic disturbance, the common ash has experienced new environmental conditions a nd the frequency of the species has fluctuated over space and time. Owing t o its ubiquity, over the last few decades the common ash has been greatly f avoured in areas abandoned by agriculture and also along impounded rivers. F: excelsior is a mesophilic species that usually thrives on alluvial soils and can also survive the strong water deficit on hillslopes. Drought toler ance in ash trees is related to stomatal regulation, a decrease in osmotic potential and also an increase in the elastic modulus epsilon. Malic acid p lays a central role in draught tolerance, first as one of the major solutes involved in osmotic adjustment, and second as an effector for stomatal reg ulation through a drought-induced increase in its xylem concentration.