5. Dr. Rakefet David-Schwartz

The planted forest in Israel is dominated by the native Pinus halepensis. Since the 1970’s, KKL-JNF has introduced the exotic Pinus brutia for afforestation because of its tolerance to the Israeli pine bast scale Matsucoccus josephi. When P. brutia and P. halepensis overlap geographically, natural hybridization occurs. These hybrids exhibit vigorous growth especially in semi-arid forests. We analyzed growth performance and physiological response to drought stress in P. brutia, P. halepensis, and their vigorous hybrids. We used rooted cuttings propagated from mature trees and utilized a high-throughput gravimetric system to measure their response to drought. A higher root-to-shoot ratio, needle length and leaf mass per area (LMA) appeared in the hybrids compared to the two parental species. P. halepensis demonstrated higher transpiration rates (E) and stomatal conductance (gsc) than P. brutia and showed an earlier reduction in E and gsc in response to drought stress. Similar to the water-saver P. brutia, the hybrids showed low E and gsc, and similarly to P. halepensis they demonstrated an early stomatal closure in response to drought. Our study suggests that the hybrids; exhibit a unique combination of traits that may contribute to forest resilience in semi-arid regions undergoing climate change.