The effect of grazing intensity and season on the soil seed bank and its relation with above-ground vegetation on the alpine steppe

The soil seed bank is a key factor in understanding the dynamics between below- and above-ground vegetation in rangelands. However, although the alpine steppe has been used to raise livestock for thousands of years, only little data are available on the impact of grazing intensity on the soil seed bank. The aim of this study was to examine whether grazing intensity on the alpine steppe of the Qinghai - Tibetan Plateau alters the size and species composition of the soil seed bank. An increase in grazing intensity decreased vegetation coverage, but did not affect species richness, the Shannon-Wiener Index and the Peilou evenness index. In addition, in general, an increase in grazing intensity increased the seed density in the persistent part of soil seed bank, but not in the transient part and, also, affected species richness. In the transient part of the soil seed bank, species richness was affected significantly by grazing intensity in May but not in November. With an increase in grazing intensity, the perennial herbaceous species increased, as did the similarity index (Cs) between the soil seed bank and above-ground vegetation. We concluded that: 1) grazing affected the seed bank and above-ground vegetation but that some responses were not in a consistent continuum with grazing intensity, that is, some increased, peaked and then decreased (“hump”-shaped) and some increased, decreased and then increased again (“N”-shaped); and 2) species with longer longevity tended to dominate under heavy grazing pressure in the alpine steppe. This study provides valuable information for the sustainable management of the alpine steppe in grazed rangelands.