Studies on Biomass and Energy Characteristics of Short Rotation Energy Plantations of Eucalyptus urophylla × E. grandis Effect of High Temperature and Drought Stress on the Physiological Characteristics of Eucalyptus urophylla×E. grandis Seedling Effect of High Temperature and Drought Stress on the Physiological Characteristics of Eucalyptus urophylla×E. grandis Seedling