Elephants as seed dispersal agents for tropical forest tree species in Kibale National Park, Uganda

The influence of elephants (Loxodonta africana) on forests has almost always been looked at in terms of destructive activities, where elephants cause tree mortality and create areas of disturbance, and not in terms of seed dispersal. The role of elephants in seed dispersal and the potential consequences of their loss for tropical forests are poorly understood. This dissertation, composed of four complementary chapters, focuses on aspects of elephant seed dispersal and its role in tropical forest tree regeneration in Kibale National Park, Uganda.; Findings indicate that the Kibale elephants are highly effective seed dispersal agents for numerous tree species and likely critical for the long-term maintenance of at least one elephant-dependent canopy tree, Balanites wilsoniana. Elephants dispersed many seeds representing more than 49 species, the majority of which were trees, recovered in elephant dung. Additionally, elephants were reliable at finding and dispersing available seeds of B. wilsoniana and other preferred fruit species. The great majority of seeds handled by elephants were ingested and passed intact with neutral or positive effects on seed germination, positive effects being most prominent in large-seeded and solely elephant-dispersed species. For B. wilsoniana, gut passage likely enhanced absolute germination success by around 66% and by 4000% relative to uningested seeds. Elephants deposited seeds in high quality sites for establishment by (1) predictably carrying seeds long distances from conspecific adults, (2) deposited seeds at lower densities than found under parent trees, (3) spreading seeds over wide areas, and (4) depositing seeds into high light and high nutrient conditions. Deposition in dung, high light conditions, and away from adult conspecifics enhanced seedling survival and growth in elephant-dispersed tree species.; As frugivores, elephants are unique because they are the sole dispersers for several species. Elephant-dispersed species are expected to decline if elephant populations decline. Elephants may also be particularly important to reforestation processes because they readily transport seeds across natural and anthropogenic boundaries.