Abstract
The present study was conducted to determine the densities and soil seed bank composition of a riparian forest and its adjacent upland vegetation for a better understanding the potentials of the soil seed banks in facilitating succession towards a more natural forest of native tree species. Three contiguous 20 m x 20 m plots were systematically established on both riparian forest and upland vegetation. Species enumeration, identification and distribution into families of the standing vegetation were carried out. Furthermore, five replicates soil samples were collected at two different depths (0-15 cm, 15-30 .The seedling emergence test was carried out for six months in the greenhouse to determine the species composition and the density of the seed in both vegetation types. The results of the seedling emergence revealed that more seeds were deposited at the upper depth (0-15 cm) than the lower depth 15-30 cm in the two vegetation types in both dry and rainy season. There was low similarity in species composition between the standing vegetation and soil seed bank in each of the two vegetation types. Herbaceous species recorded the highest number of seedlings as compared to the other habit. The low similarity between seed bank and standing vegetation of the riparian forest and the adjacent upland vegetation suggested that soil seed bank was insignificant in their restoration.
Highlights
Riparian forests are one of the biospheres’ most complex ecological systems and are important for maintaining the vitality of landscape and its rivers (Naiman and Decamps, 1990; 1997)
Species composition of the standing vegetation In the riparian forest thirty-eight woody species were encountered while forty woody species were encountered in the upland vegetation
Seedling emergence at 0-15 cm depth In the dry season, a total mean of 107 seedlings or 640 seeds/m2 emerged in the riparian forest at 0-15 cm depth (Table 3)
Summary
Riparian forests are one of the biospheres’ most complex ecological systems and are important for maintaining the vitality of landscape and its rivers (Naiman and Decamps, 1990; 1997). Vegetation in riparian areas is generally characterized by its high species richness and has unique characters making it different from the upland vegetation (Naiman et al, 1993) Despite their limited area extent, riparian areas promote many ecosystem functions vital to the health and productivity of forested watersheds (Gregory et al, 1991). The riparian areas regulate the flow of water, sediments, and nutrients across system boundaries; they contribute with organic material to the aquatic system, increase bank stability, reduce erosion, and provide key wildlife habitat (Gregory et al, 1991) Because of their functional importance, riparian areas play important roles in reducing many of the negative impacts of land use on aquatic systems as well as protecting species diversity, providing potential dispersal corridors for wildlife, and reducing flood waters (Ilhardt et al, 2000). In order to understand the soil seed bank dynamics in degraded forests, which include gains through seed rain, losses due to seed predation, seed death and transfer into the active seed bank to germinate and form a seedling bank, is necessary before deciding whether intervention is needed to assist the natural regeneration process (Augusto Uasuf et al, 2009)
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