Species richness, diversity, density, and spatial distribution of soil
seed banks in the Moremi Game Reserve Riparian Woodlands of the Okavango
Delta, northern Botswana
Abstract
This study aimed to investigate the soil seed banks in the Moremi Game
Reserve Riparian Woodlands (hereafter MGRWs) of the Okavango Delta,
northern Botswana. We determined diversity indices, densities, spatial
distribution of seeds in the soil, and compared the similarity in
species composition between the standing vegetation and soil seed bank
flora. The vegetation was sampled in 42 plots (20 × 50 m) and soil
samples were collected from 336 subplots. Soil seed bank communities
were determined using agglomerative hierarchical cluster analysis.
Indicator values were calculated using indicator species analysis for
species in each community of germinated seeds and across different soil
layers. To infer spatial relationships of soil layers in terms of soil
seed bank composition Bray-Curtis ordination was used. A total of 124
plant species were identified in the litter and top 9 cm soil layers
with a mean density of 1,933 seeds m-2. Herbs, grasses, sedges, and
woody plants were represented by 69, 25, 17, and 13 species,
respectively, in 33 families and 92 genera. The overall diversity and
evenness of the soil seed bank in the MGRWs were 3.7 and 0.77,
respectively. The results revealed that Poaceae, Cyperaceae and
Asteraceae are the most dominant families in all the germinated species.
Four plant communities, namely Kohautia virgata-Ammania baccifera,
Bidens pilosa-Urochloa mosambisensis, Setaria verticillata-Brachiaria
deflexa, and Cynodon dactylon-Cyperus longus were identified from the
soil seed bank. Bray-Curtis ordination showed that there was an overlap
between these communities in terms of seed bank composition. However,
MRPP analysis showed that there was significant (P < 0.05)
separation between germinated soil seed bank communities. The overall
spatial horizontal distribution of seeds varied among sampling quadrats
while the vertical distribution of seeds exhibited the highest densities
occurring in the upper 3cm of the soil and gradually decreasing
densities with increasing depth.