Regenerative potential and functional composition of soil seed banks in remnant evergreen broad-leaved forests under urbanization in South China

Soil seed banks can act as an important source in forest regeneration, and the information on the seed bank composition is vital for determining the resilience of plant communities under severe environments such as urban settings. In this study, we examined the seed bank density and functional composition, and their relationships with aboveground vegetation in three remnant evergreen broad-leaved forests, i.e., PuGang (PG), LuoGang (LG), and DaLingShan (DLS) under urbanization in Guangzhou, South China. In both years of our study (2010-2011), seed density and species richness for overall soil seed banks and each classified life forms (tree, shrub, herb and grass) significantly differed among the forests and were much higher in the PG forest. The prevailing life forms in the seed banks were herbs and grasses, and the proportion of tree species Importance Value index (IV) of the seed banks was low. We did not detect significant difference in the percentage of exotic species seeds in the seed banks among the forests. The proportion of species with animal dispersal mode was much higher in the DLS forest than in the PG and LG forests. The similarity in species composition between standing vegetation and seed banks was low with the lower value in the DLS forest than in PG and LG forest. Our findings suggest that the regeneration potential of the soil seed banks is limited for the remnant forests in urban areas. Therefore, greater proactive and enhanced conservation efforts are thus needed. Nomenclature: Wu and Raven (1994). Abberviations: IV–Importance Value, DLS– DaLingShan, LG– LuoGang, LSD–Least Significant Difference, PG– PuGang. Regeneration of seed banks in broadleaved forests 87 the knowledge of the soil seed banks is vital for determining the resilience of a plant community, because the seeds stored in the soil may recruit new seedlings when disturbance creates suitable environmental conditions (Dölle and Schmidt 2009). Seed bank composition depends on the seed storing conditions in the soil affected by biotic and abiotic factors such as predation, soil temperature, and litter mass on the floor (Maron and Simms 1997, Hill and French 2003, Wang et al. 2009). Urbanization related disturbances may influence these factors and thereby affect the seed bank composition (Kostel-Hughes et al. 1998). Furthermore, the aboveground vegetation in the community also directly influences the composition of soil seed banks. Therefore, knowing the relationship between seed banks and aboveground vegetation can be helpful in planning community in responses to disturbances (Bossuyt and Honnay 2008), Currently, many studies have focused on structure and diversity of aboveground community in the forest under urbanization, but soil seed banks have been overlooked (Pellissier et al. 2008, Huang et al. 2012). In this study, we investigated the density and species composition of the soil seed banks in three evergreen broadleaved forests under urbanization in South China. Our main objectives were to determine the seed bank density, functional composition and its relationship with aboveground vegetation in the remnant natural forests, and also to evaluate the regenerative potential of the soil seed banks. Specifically, we sought to answer the following questions: (1) How do the size, species richness, diversity, and functional composition of soil seed banks differ among the three remnant forests under urbanization? (2) What are the similarities in species composition between the seed bank and aboveground vegetation? And (3) What are the roles of the soil seed banks in the regeneration of these remnant forests under urban settings? Materials and methods