Comparing seed removal rates in actively and passively restored tropical moist forests

Abstract

High rates of seed removal can impede forest recovery, but tropical seed removal studies are few and mainly from the neotropics. Little is known about the comparative influences of active restoration (i.e. planting) and passive restoration (i.e. protection of natural regrowth) on seed removal. We conducted an evaluation of seed removal in grasslands, natural forests (tropical moist semideciduous forest), and actively (21‐, 17‐, 16‐, 11‐, 8‐, and 6‐year‐old) and passively (21‐year‐old) restored forests in Kibale National Park, Uganda. We wanted to compare the effect of vegetation type, time since restoration and restoration actions (i.e. active vs. passive) on removal of seeds of five animal‐dispersed tree species during wet and dry seasons. Seeds were either fully exposed or placed in closed mesh cages or under a mesh roof. We used differential removal rates between these treatments to attribute seed removal to different animal taxa. Seed removal rate (percentage of seed removed over a 4‐day period) was highest in passively restored forests, compared with actively restored forests, grasslands, and natural forests. We detected no significant relationship between time since restoration and seed removal rates within actively restored sites. Seed removal rate from roofed treatments was not significantly different from removal from open treatments but was significantly higher than removal from closed treatments, which we interpret as reflecting the greater effect of small mammals versus insects. Smaller seeds tended to be removed at a greater rate than larger seeds. We discuss the implications of these findings for forest regeneration.

Tree seed rain and seed removal, but not the seed bank, impede forest recovery in bracken (Pteridium aquilinum (L.) Kuhn)‐dominated clearings in the African highlands

“…For example, even if forest and bracken started with the same seed number, maintaining the same 3‐day rate of seed removal over a 30‐day interval would result in more than 800 times more seeds in the forest. Other studies have also reported a significantly higher rate of seed removal in treeless areas than in nearby forest (in Indonesia, Blackham & Corlett, ; in Netherlands, den Ouden, ; and in Madagascar, Razafindratsima, ) although such patterns are not universal, for example, grassland versus forest in Kibale Forest in Uganda (Ssekuubwa, Loe, Sheil, Tweheyo, & Moe, in press).…”

Colonization of woody seedlings in the understory of actively and passively restored tropical moist forests

“…Ssekuubwa et al (2018) showed that seed removal in our study sites was not influenced by restoration age. If we interpret seed removal as secondary seed dispersal (Vander Wall et al 2005), then the seed removal rates reported by Ssekuubwa et al (2018) could indicate a uniform availability of seeds for germination among restoration sites of different ages. Thus, seedling colonization in our sites may be more microsite-limited than seed-limited.…”

“…Seed predation impedes seedling colonization (Holl et al 2000) while dispersal improves colonization of seedlings (García et al 2005). More recently, Ssekuubwa et al (2018) showed that the rate of removal of seeds of woody species in our sites was higher for passively than actively restored forests. If the seed removal guild in our sites is composed of more seed dispersers than predators, then possibly more seeds reach suitable microhabitats for germination, and seedling predation is reduced, which increases colonization in passively restored forests.…”

“…Plant populations may be seed-limited or microsite-limited, which potentially reduces seedling colonization in restoration sites (Wijdeven & Kuzee 2000). Ssekuubwa et al (2018) showed that seed removal in our study sites was not influenced by restoration age. If we interpret seed removal as secondary seed dispersal (Vander Wall et al 2005), then the seed removal rates reported by Ssekuubwa et al (2018) could indicate a uniform availability of seeds for germination among restoration sites of different ages.…”

Semeadura direta para restauração florestal e seus efeitos sobre comunidades de formigas e interações ecológicas

“…Com a reestruturação da comunidade animal, processos ecológicos tendem a ressurgir e se intensificar. A remoção de sementes é um processo ecológico importante para avaliar a recuperação de ecossistemas funcionais e pode afetar a composição de espécies vegetais que se estabelecem nos locais perturbados e em restauração (Queiroz et al 2021;Ssekuubwa et al 2018). Entre os insetos, os principais agentes de remoção são as formigas e estas podendo atuar como predadores ou dispersores (Vander Wall et al 2005).…”