1. Ecological and Environmental Characteristics in the Hilly Region of Middle and Lower Yangtze River

The Yangtze River is one of the most important rivers in the world. Its middle and lower reaches lie in the subtropical monsoon area of east Asia, which has a warm and moist climate with clear distinction between the four seasons. The vegetation in the middle and lower reaches of Yangtze River takes on conspicuous vertical zoning characteristics. From low to high elevation, the vegetation makes a transition from evergreen broadleaf forest to mixed evergreen broadleaf and deciduous forest. The species diversity of forest plantations in the middle and lower reaches of the Yangtze River has very important status in China. The present problems of soil erosion are based mainly on the following factors: (1) plentiful precipitation provides strong force for water erosion; (2) the inhomogeneities in the temporal and spatial distributions of precipitation result in both frequent flood and drought calamities; (3) simple forest structure and monocultures of trees cause fragility of the forest ecosystem; (4) the sharp increase of population has made the forest destruction more serious and has caused flooding. Because water and soil loss has constrained the development of eastern China, the control of soil loss has been deemed as of primary importance in reforestation.