Soil Seed Bank Characteristics of the Mbe and Nguela Shrub Savannas, and Implications for the Reforestation, Republic of Congo

The soil seed bank is an important source of restoration and resilience of disturbed ecosystems. This study evaluates the regeneration potential through the soil seed bank of the shrub savannas of Nguela and Mbe in order to predict the eventual dynamics. Three plots of 0.25 ha subdivided into four sub-plots of 0.015 ha have been installed in each savannah. In total, 48 samples of each savannah, i.e. 96 samples of both savannas, have been taken from the soil layers, 0 - 5 cm, 5 - 10 cm, 10 - 15 cm and 15 - 20 cm. Species diversity and abundance of the soil seed bank have been assessed after germination. The results reveal 167 seedlings belonging to 23 species in the Mbe savannah and 144 seedlings belonging to 14 species in the Nguela savannah. The total densities of the germinated seeds were respectively 463.63 seeds/m2 and 400 seeds/m2. Nevertheless, the 20 cm deep layers have illustrated themselves compared to the superficial layers with densities of 16.29 seeds/m2 and 21.66 seeds/m2, respectively, in the savannas of Mbe and Nguela. Herbaceous species largely dominated, with percentages of 91% and 100%, respectively, in the savannas of Mbe and Nguela. Alone, the Trema orientalis (L.) Blume species has been identified as woody species in the Mbe savannah. The greatest specific richness has been obtained in the first five centimeters of soil, with 21.73% and 28.57% of exclusive species, respectively, in the savannas of Mbe and Nguela. The results reveal that restoration through the soil seed bank would be limited to a single woody species found (T. orientalis). Consequently, the study suggests silvicultural interventions based on planting or enrichment techniques for sustainably managed savannas exposed to anthropogenic disturbances.

Soil Seed Bank of the Marantaceae Forests of Ouesso Forest Industry (IFO), Republic of Congo

The soil seed bank is a key indicator of natural regeneration and/or forests resilience after disturbances. This study evaluates the soil seed bank characteristics in two Marantaceae forests plots of Ouesso Forest Industry (IFO) in north of the Republic of Congo. In each plot, 12 samples were taken per soil layers (0 - 5 cm, 5 - 10 cm, 10 - 15 cm and 15 - 20 cm deep). Diversity and abundance seed were estimated after germination of soil samples. The results revealed 101 seedlings belonging to 17 species for plot 1 and 129 seedlings belonging to 15 species for plot 2. The average densities of germinated seeds were respectively 281 seedling/m2 and 358 seedling/m2. There were no significant differences (p > 0.05) between the mean densities of the two plots. Herbaceous species dominated with percentages of 71% and 73%, respectively in plot 1 and plot 2. Both plots showed potential of regeneration from the soil seed bank. However, this potential seems higher in plot 2. Pioneer taxa were more abundant in the soil seed bank of plot 1 (4 woody pioneer species) than in plot 2 (1 woody pioneer species). The highest species richness was obtained in the first two soil layers (0 - 5 cm and 5 - 10 cm depth) while 25% of species were exclusively found in the deepest layer (15 - 20 cm) in plot 2. The study suggests silvicultural interventions based on planting or enrichment techniques for contribute to sustainable management of Marantaceae forests that could prevent the growth and development of seedlings.

Soil Seed Bank Characteristics in Congolese Rainforests and Implications for Post-Logging Plots Reforestation

The soil seed bank is considered as an important mechanism for the natural regeneration, resilience and conservation of the forests after disturbances. This study evaluates the characteristics of the soil seed bank in two post-logging plots of Loundoungou-Toukoulaka Forest Management Unit: one plot exploited in 2008 and another exploited in 2021. In each study plot, 40 samples were collected per soil layer (0 - 5 cm, 5 - 10 cm, 10 - 15 cm, 15 - 20 cm and 20 - 25 cm depth). The species diversity and abundance of the soil seed bank were estimated after soil samples were brought to germination. The results demonstrated that 347 seedlings belonging to 37 species in the plot exploited in 2008 and 418 seedlings belonging to 27 species in that exploited in 2021 germinated during 20 weeks of monitoring. The total densities of the seedlings identified were respectively 1446 seedlings/m2 and 1742 seedlings/m2. The plot exploited in 2021 presented a higher proportion of herbaceous species (93.78%) compared to that exploited in 2008 (82.71%). Two pioneer species were recorded in the plot exploited in 2008. These are Macaranga barteri (0.29%) in the 0 - 5 cm layer and Musanga cecropioides (2.31%) up to 20 cm deep. On the other hand, in the plot exploited in 2021, Macaranga spinosa (0.96%) in the 0 - 5 cm layer and M. cecropioides (0.96%) up to 20 cm deep were identified. In the plot exploited in 2008, the 20 - 25 cm layer demonstrated important proportions in woody species (9%), these are in particular Rubiaceae sp.4 and Nauclea diderrichii. While that exploited in 2021, presented 19% of woody species, namely the species of Rubiaceae sp.4, Rubiaceae sp.5 and N. diderrichii, greatly exceeding the proportions obtained in the 15 - 20 cm layer of the two plots. Nonetheless, N. diderrichii was the only commercial species recorded with densities of 108 seedlings/m2 and 4 seedlings/m2, respectively in the plot exploited in 2008 and that exploited in 2021. Commercial tree species are poorly represented in the soil seed bank. Consequently, the study suggests that to improve the natural regeneration of the commercial species, silvicultural interventions based on planting techniques in the exploited plots should be more effective in order to sustainably manage these production forests.

Regeneration Potential of Woody Species at the Side of Secondary Roads Post-Logging of Loundoungou-Toukoulaka Forest Management Unit, Republic of the Congo

Natural regeneration is the basis of a dynamic and demographic balance of plant populations. The objective of this study was to assess the natural regeneration potential of woody species along secondary roads post-logging abandoned since 2008 and 2018. In the two Annual Allowable Cuts (AAC 2008 and AAC 2018), 24 regenerating sub-plots (i.e. 12 sub-plots for AAC 2008 and 12 sub-plots for AAC 2018) with a unit area of 5 m × 5 m were delimited with a total area of 0.06 ha (i.e. 0.03 ha for each AAC). The abundance and diversity of woody species were respectively inventoried and estimated. Two estimators of the specific richness were used to estimate the floristic diversity of each Annual Allowable Cuts (AAC). The results reveal globally 88 woody species in the AAC 2008 and 241 woody species in the AAC 2018, with respective average densities of 2933 stem/ha and 8033 stem/ha. There was a very highly significant difference between the mean densities of the two AAC (Kruskal-Wallis test;H = 2.36, p-value < 0.000). The results also highlight a great diversity and a relatively high abundance of woody species in the 2018 AAC compared to the 2008 AAC. Also, the spatial structuring of the sub-plots on the basis of Principal Component Analysis (PCA) demonstrates that the floristic composition of the two AAC is globally different. The study suggests silvicultural interventions and the long-term assessment of regenerating woody species along abandoned secondary roads in order to guarantee the sustainable management of their population.