Vulnerability to xylem embolism as a major correlate of the environmental distribution of rain forest species on a tropical island

Increases in drought-induced tree mortality are being observedin tropical rain forests worldwide and are also likely to affectthe geographical distribution of tropical vegetation. However,the mechanisms underlying the drought vulnerability and environmental distribution of tropical species have been little studied. We measured vulnerability to xylem embolism (P50) of 13woody species endemic to New Caledonia and with differentxylem conduit morphologies. We examined the relation be-tween P50, along with other leaf and xylem functional traits,and a range of habitat variables. Selected species had P50values ranging between 4.03 and 2.00 MPa with most species falling in a narrow range of resistance to embolism above 2.7 MPa. Embolism vulnerability was significantly correlatedwith elevation, mean annual temperature and percentage ofspecies occurrences located in rain forest habitats. Xylem conduit type did not explain variation in P50. Commonly used functional traits such as wood density and leaf traits were notrelated to embolism vulnerability. Xylem embolism vulnerability stands out among other commonly used functional traits as amajor driver of species environmental distribution. Drought-induced xylem embolism vulnerability behaves as a physiological trait closely associated with the habitat occupation of rainforest woody species.