Land use has little influence on the soil seed bank in a central African moist forest

Regeneration of tropical forest occurs naturally and mainly through early secondary succession by soil seed banks. Here, we analyzed seed bank variation in density and diversity along a degradation gradient. We also explored the relationship (similarity in composition) between the seed and seedling banks and the overstory vegetation. The investigated forests were located at Dja Fauna Reserve and its surroundings, south-eastern Cameroon. We sampled 33 one-ha forest plots scattered in a protected area, in a logging concession and in community forests. Within each plot, we inventoried the seed bank in the litter and in four successive soil layers of 5 cm depth interval, and the standing vegetation. Seed density significantly varied with sampling depth but not between land use types. A total of 181 morphospecies were identified. Trees species accounted for 46% of seeds with pioneer species dispersed by animals dominating the seed bank. Species diversity and composition strongly varied with the sampling depth; the litter seed bank was more similar in composition to the soil seed bank than to the seedling bank, sapling, and forest stands. We highlighted the presence of a dense and diverse seed bank in each land use type. We also showed the differentiation of each sampling depth in terms of species composition, thus revealing their complementarity in the dynamics of natural regeneration. The dominance of pioneers in the seed bank and weak relationship with the overstory are universal for tropical forests and logically follow from forest succession after disturbance. Abstract in French is available with online material.

Automated summary

The study analyzed the variation of seed banks in forests in southeastern Cameroon, finding that seed density varied with sampling depth, while species diversity and composition were influenced by sampling depth. The seed banks at different sampling depths showed complementarity, and had a weak relationship with the overstory vegetation.