Environmental Heterogeneity and Population Variability of Sclerophyllous Oaks (Quercus Sec. suber) in East Himalayan Region

This paper studied the morphological variations and genetic distances among sclerophyllous oak (Quercus Sec. suber) species in Tibet and Yunnan of East Himalayan region (26~33 °N; 90~101°E) and in Sichuan of Southwest China. It showed that these oaks varied from big trees to small shrubs with the altitude increase and precipitation decrease in the natural conditions. The variable climates and intensive topographies of the region provided many possibilities for the oak population changes in morphology, growth -form and genetics.Inter -and intra -population genetic distances varied drastically with local habitats, mountain topographies, and dominant currents rather than horizontal distances. Tibet site is charac-terised by the precipitous topography and diverse climates, while Yunnan site by high mountains and deep valleys. Their mean inter -population genetic distances of the sclerophyllous oaks are 0.396 and 0.365, respectively, but the former is significantly higher than the later (P < 5%). Both of them are extremely higher than that (0.222) of Sichuan site (P < 0.1%). It suggested the more heterogeneous the environments the more variable the sclerophyllous oaks.Population variability and species evolution associated with the environmental heterogeneity such as climate, local dominant current, habitat, topography and soil. The morphological responses in leaves, shoots and roots of the East Himalayan sclerophyllous oaks to the environmental heterogeneity are the same as that the Mediterranean-climate plants even they distributed under a monsoon continental climate. Regional environmental heterogeneity must have brought about the species evolution and population variations.The high similarities in these sclerophyllous plants be-tween the two climate regions indicated that they might origin from a common ancestor and have the same adaptive strategies to the environmental stress.