The simulation study of the rehabilitation of ecological environments and the sustainable developments of agriculture, forestry, animal husbandry in the loess hilly regions in Shanxi Province, Shaanxi Province and Ningxia Automous Region Community characteristics of natural Pinus tabulaeformis forest in Hilly Loess Regions Structures and Diversity of Insect Communities under Different Types of Vegetation Rehabilitations of the Hilly and Gully Loess Regions Spatial Growth Differences of Planted Populus simonii and Their Ecological Effects on Soil Moisture in Hilly Loess Regions