The soil seed bank is important for vegetation regeneration and natural succession, and it may change as a result of management, for example in response to varying grazing pressure. However, almost nothing is known about the on the soil seed banks in the restored steppe, and steppe degraded by grazing in Inner Mongolia. Here, we aimed to: (1) investigate the composition and soil seed density in three vertical layers in restored steppe after long-term exclusion (10 and 23 years) of grazing, and compare this with steppe degraded by grazing; (2) examine and compare the total and persistent soil seed bank in restored steppe versus degraded grazing steppe; (3) relate the similarity of seed bank composition with that of the standing vegetation.
In August 2004, we investigated the community of three sites in Xilingole: (1) two areas of previously degraded steppe where grazing had been excluded for either 10 or 23 years, and (2) a degraded steppe where grazing had been continued. The species present in the vegetation was assessed using five 1m 1m quadrats distributed randomly in each area. In spring 2005, in the same sites, fifteen soil cores (15 cm×15 cm×3 cm) were collected from three depth layers (0-3 cm, 3-6 cm and 6-9 cm) for each three treatments. The composition and density of the soil seed bank was evaluated by monitoring seedling emergence. The similarity of soil seed bank and the standing vegetation was assessed using the Sorensen index.
Heavy grazing can cause the lack of soil seed reserves, and long term-grazing exclusion can restore the composition and density of soil seed banks steppe. In April 2005, the total soil seed banks (0-9 cm depth) after 10 and 23 years enclosure had 4756 and 4433 seeds•m-2 respectively but only 856 seeds•m-2 for the degraded steppe. In June results were lower but showed the same pattern (i.e. 2255, 2333 and 778 s seeds•m-2). The difference in results between April and June can be considered as the spring germinable seeds. The persistent soil seed banks of the 10, 23 years enclosed steppe, and degraded steppe were 53%、47% and 91% of the total soil seed bank. Most soil seeds were found in the top 0-6 cm, and there was a decrease with depth. Annuals constituted a major component of the steppe soil seed bank, and most seeds were classified as transient members of the transient soil seed bank, such as annual Chenopodium album and perennial Allium tenuissimum. The Sorensen similarity index of seed bank composition and standing vegetation was 0.49-0.54.