Low recruitment of trees dispersed by animals in African forest fragments

We investigated the effects of forest fragmentation on the disappearance of fruit-eating animals and the recruitment of animal-, wind-, and gravity-dispersed trees in 80-year-old forest patches in the East Us- ambara Mountains of Tanzania. We compared adult and juvenile trees in forest transects in a 3500-ha submontane forest with those in four forest fragments of 521,30,9, and 0.5 ha. Preliminary results show that recruitment of seedlings and juveniles of 31 animal-dispersed tree species was more than three times greater in continuous forest and large forest fragments (greater than or equal to 30 ha) than in small forest fragments (less than or equal to 59 ha), whereas recruitment of eight wind- and gravity-dispersed trees of the forest interior was unaffected. Recruitment of 10 endemic, animal-dispersed tree species was 40 times lower in small fragments than in continuous forest or large fragments. Counts of diurnal primates and birds in all five sites indicated that frugivorous species have declined with decreasing fragment size. These results are consistent with the idea that loss of dispersal agents depresses tree recruitment in the course of forest fragmentation.