Composition, species richness, and density of the germinable seed bank over 4 years in young and mature forests in Brazilian semiarid regions

• A total of 121 native species emerged from the soil seed bank.
• Floristic composition of young forest differs from that of mature forest.
• Species richness of mature forest was higher only in the rainy season.
• The average seed density of mature forest was also higher.
• The average density of both forests was higher in the dry season.

The soil seed bank is an important ecological component in forest regeneration. In semiarid regions, forest regeneration is highly affected by seasonal and interannual variations in precipitation, because these variations may affect the composition, species richness, and density of seeds in the soil. This study aimed to characterize and compare these parameters of the germinable seed bank in fragments of young and mature Caatinga forest between various seasons and over consecutive years. A total of 105 soil samples were collected in 20 × 20 × 5 cm plots in each forest (Young and Mature) at the end of the rainy and dry seasons over 4 years (2009–2012), totaling 840 samples. The composition, species richness, and density of seeds were determined by the method of seedling emergence. Over the 4 years, 121 species emerged from the soil seed bank, 86 in the young forest, and 109 in the mature forest. Significant differences in the composition, richness, and density were recorded between forests, seasons, and years, with a significant interaction between them. Relationship between rainfall and age of forests affects the dynamics of the soil seed bank in semiarid environments, which are important distinctions for the maintenance of these areas.