Tree Recruitment from On-site Versus Off-site Propagule Sources During Tropical Forest Succession

The management of successional forests has become an increasingly important tool for tropical forest restoration on disturbed lands. Successful management depends on understanding factors governing tree recruitment during succession. Recruits can be on-site propagules surviving disturbance (e.g. saplings) or seeds arriving after disturbance. Among disturbed sites, the importance of seed arrival from off-site should increase as availability of on-site propagules declines. This study examines how seed arrival from off-site seemed to influence natural forest regrowth on logged plantations in Uganda. Specifically, the effect of seed arrival from mammals (determined directly) and birds (determined inferentially) was estimated in two plantations with high and three plantations with low quantities of saplings surviving logging. In both plantation types, first-year recruitment seemed to originate from on-site (seed bank and sprouts from damaged trees) and off-site sources (seed-dispersing birds). Recruitment declined 2–3 years after logging in all plantations despite high densities of seed-dispersing birds. Recruitment was generally greater in plantations with low initial quantities of on-site propagules, and by 4–6 years forest structure was similar between plantation types. Recruitment was dominated by bird-dispersed species, rather than mammal- or wind-dispersed species. Taken together, these results illustrate that disturbed areas with low initial on-site propagule availability have much potential for forest regrowth.