Drought-induced mortality and hydraulic architecture in pine populations of the NE Iberian Peninsula

Abstract

The summers of 1994 and, to a lesser extent, 1998 were particularly dry in eastern Spain. As a result, several plant species were severely affected. We estimated drought-induced mortality in several populations of three pine species that co-exist in the study area ( Pinus nigra, P. pinaster and P. sylvestris). Hydraulic conductivity, vulnerability to xylem embolism, and tree-ring width were also measured for each population. Results showed that mortality only affected P. sylvestris, and that there were significant differences between two populations of this species. Although maximum hydraulic conductivity and vulnerability to embolism were almost identical among species and populations, they differed in other aspects of their hydraulic architecture. In particular, (1) hydraulic conductivity per unit of leaf area was lower in the most acutely affected P. sylvestris population. Lower leaf specific conductivity causes higher water potential gradients and, hence, higher levels of embolism (if vulnerabilities are alike). We suggest that this difference was the main cause of the observed mortality pattern. (2) P. pinaster showed higher water-use efficiency (WUE) (inferred from δ 13C data) than the other two species. Regarding the response to drought at the population level, the most affected P. sylvestris population slightly increased growth after the 1994 drought, which we relate to a relaxation of competition among surviving individuals. The important drought-induced mortality observed in the study area suggests that drier climate (as predicted by climate change simulations) may endanger several P. sylvestris populations in the Mediterranean basin.