All viable seeds present on or in the soil or associated litter constitute the soil seed bank. Seed bank input is determined by the seed rain. Seed rain comes from seed dispersion from mother plants and also from secondary dispersion. Seed losses result from germination, animal predation, deep burial, redispersal, natural senescence and death caused by pathogens and some animals. Seeds in the soil display horizontal and vertical dispersion, reflecting initial dispersal onto the soil and subsequent movement. Investigation of die seed and spore bank has become a recognized and indispensable part of plant ecology now and has been an active research area. The soil seed bank is one of the life history stages of plant populations, which is called subpop-ulation stage. Some soil seed bank classification methods had been provided by scientists, but simply the soil seed bank can be classified into the transient soil seed bank, with seeds that germinate within a year of initial dispersal, and the permanent soil seed bank, with seeds that remain in the soil more than one year. Even given ideal germination conditions such as season, temperature and moisture, some seeds in the soil still remain dormant; these comprise the persistent soil seed bank. Temporal and spatial heterogeneity is the basic characteristic of the soil seed bank. Not only are the floristic composition, size and diversity of the soil seed bank different in different plant communities, but microsites or microhabitats greatly affect the distribution patterns of the soil seed bank.
The number of reproductive individuals existing in a dormant state is significantly greater than that of aboveground individuals in most habitats dominated by higher plants. Because of reasons such as germination, predation and decay, soil seed banks have seasonal dynamics. The soil seed bank, seedling bank and adult vegetation can interconnect and interact with each other. The relationship between soil seed banks and their aboveground vegetation is similar or dissimilar because of different plant community types, different succession stages and different sampling time. Germination in the greenhouse and physical separation methods were used to research the soil seed bank. The soil seed bank can partly reflect the history of communities, and plays an important role in the restoration of degraded ecosystems. The main hot topics about soil seed bank research are summed up as following: 1) the research methods about soil seed banks; 2) the classification of soil seed banks; 3) the temporal and spatial distribution patterns of soil seed banks; 4) the relationships between aboveground vegetation and soil seed bank; 5) the dynamics of soil seed banks.