Soil Seed Bank Composition and Diversity in Areas Invaded with Invasive Alien Species in the Lower Montane Forest of Kilimanjaro National Park, Tanzania

Knowledge of soil seed banks is crucial for the management of invasive alien species (IAS) and restoration planning of disturbed ecosystems. This study compared seed density and species composition of soil seed banks in areas invaded by IAS in the lower montane forest of Kilimanjaro National Park. Five sites were identified: four sites dominated by distinct invasive IAS, namely Acacia mearnsii, Cupressus lusitanica, Eucalyptus spp., and Pinus patula, and one site with natural forest. Soil samples were collected from ten plots (each 10 × 10 m) established in each vegetation site at three depth classes, making a total of 150 samples for the five sites. A seedling emergence method was employed to assess seed density, and species of emerged seedlings were identified. A total of 5,942 seeds belonging to 100 species, 82 genera, and 41 families germinated from the soil samples. The germinating seeds were composed of herbaceous plants, grasses, and a few woody species. The topsoil (1–5 cm) exhibited significantly higher seedling density than the litter fall and subsoil (6–10 cm) layers (F (2, 174) = 13.3, p < .001). The P. patula site exhibited the highest soil seed bank density (seedlings/m²) among all the sites studied, and the variation was statistically significant (F (4, 161) = 16.7, p < 0.001). The investigated sites exhibited a high number of undesirable seeds of invasive alien species such as A. mearnsii, P. patula, Grevillea robusta, and Poa annua. These findings highlight that the lower montane forest of Kilimanjaro National Park is rich in soil seed banks dominated by non-woody species and a few woody species. Therefore, forest restoration after the control of IAS may depend not only on the persistent soil seed bank but also on dispersal mechanisms from elsewhere and reforestation techniques.