The growth of plants, or the development of vegetation, is controlled by ecological factors (natural conditions). Ecological factors are mainly sunlight, temperature, moisture, minerals (soil), oxygen, carbon dioxide and so on. Among them, the first four factors, namely sunshine, temperature, moisture and minerals, have great regional changes and certain distribution laws. In other words, the distribution of vegetation is mainly related to climate and soil. The transformation and utilization of vegetation by human beings can not be separated from certain climate and soil conditions. Natural vegetation is the product of the long-term historical development of plants that appear in a region. The unit of vegetation is plant community, and the vegetation in a certain area can be composed of a single community or several communities. For example, the vegetation in Changbai Mountain is mainly composed of forest communities, while the vegetation in North China is composed of forest, shrub and meadow communities. Vegetation is a gene bank, which preserves a variety of plants, animals and microorganisms and provides various important and renewable natural resources for human beings.