Studies on the Characteristic of Element Contents in the Dominant Plant Species of the Threegorges Region in China A vertical gradient analysis of the flora of Dalaoling Mountain in the Three Gorges region, China PLANT SPECIES DIVERSITY OF THE DEGRADED ECOSY STEMS IN THE THREE GORGES REGION Effect of the Previous Crops on the Initial Stage of Establishment of a Mixed-Sowing Grassland Studies on the Biomass of Typical Scrubland and Their Regeneration Capacity After Cutting