Changes in soil seed bank composition during early succession of rehabilitated quarries

To evaluate the contribution of seed bank to natural revegetation, a soil seed bank study was carried out at different phases on three quarries in Hong Kong. A total of 2188 seedlings from 57 species were found, among which 36 species were herbaceous and graminoid plants while 21 were woody species. The soil seed banks were dominated by a few annual species, i.e. Ageratum conyzoides, A. houstonianum, Cynodon dactylon, Digitaria longiflora and Kyllinga brevifolia, which accounted for more than 35% of the total abundance. With ecological development, greater species number as well as seed density and diversity were recorded at older rehabilitated sites, which indicated that the process favors the increase in species richness. However, non-woody species predominated in all phases including those that were even more than 10 years after rehabilitation. The result of DCA showed that only 21 woody species which included 15 native species were better represented on the older quarry sites, which may still be insufficient to initiate natural succession at the later successional stage. As most native species in the soil seed banks were dispersed by birds, management strategies should take into account the possibility of enrichment planting with native species in the early stage and sowing some late successional species in the later stage for quarry rehabilitation.