Seed Dispersal and Potential Forest Succession in Abandoned Agriculture in Tropical Africa

Background

Forest succession on disturbed and post-agrarian lands is often slow because the resources necessary for succession – such as soil nutrients, seeds, and moisture – are depleted. In such areas, succession may depend on bat- and bird-dispersed seeds arriving from distant forest patches.

Research goals & methods

The study reports on bat and bird seed dispersal in a deforested agricultural area adjacent to Kibale National Park, Uganda. Seed rain was monitored for 6 months in short (<0.5m) and tall (2-5m) grassland, and below isolated short, medium, and tall trees within grassland. Over 11000 seeds were collected. Seed rain quantity and species richness were greater below trees of all heights than in grassland alone, and greatest below tall trees. Bats dispersed seeds mostly below tall trees (>10m), while birds dispersed seeds mostly below tall and midsized trees (>3.5m).

Conclusions & takeaways

Nearly half of the seeds collected were from hemiepiphytic Ficus. One third were from shrubs and the remainder were from trees. Nearly all tree and shrub seeds collected were of species typically found in disturbed grassland, not in forest. These findings suggest that in this region, natural forest succession may proceed very slowly on degraded lands.