The effect of forest fragmentation on the soil seed bank of Central Amazonia

Deforestation of tropical forests has contributed to the formation of fragmented landscapes, surrounded mainly by a matrix of secondary forests, pastures and agriculture. In this study we evaluated the fragment-area effects on the density, diversity and composition of the soil seed bank. Fragments of primary forest of different sizes (1, 10 and 100 ha) and continuous primary forests were sampled in a region of terra firme forest in Central Amazonia. We collected 180 soil samples (45 samples per treatment), and monitored seedling emergence from the soil seed bank in a greenhouse for seven months. Density of emerged seedlings, floristic composition, richness and diversity of species were compared among treatments with Kruskal-Wallis non-parametric test, Mann-Whitney test, Fisher's Alpha diversity index and Non-metric multidimensional scaling (NMDS). Seedling density was inversely proportional to the size of the fragment, being higher in fragments of 1 ha, 10 ha, and lower in the primary forest and fragments of 100 ha. Diversity was higher in the fragments when compared to the primary forests. Melastomataceae was the most abundant family in all treatments. Species composition changed along the disturbance gradient, and is dominated, in the smaller fragments by species that are indicators of degraded environments. Results suggested that the area of the forest fragments affects the size and composition of the soil seed bank, and can significantly influence the potential resilience and regeneration of these sites in the event of natural or anthropic disturbance.