Data from: Successional status, seed dispersal mode and overstorey species influence tree regeneration in tropical rain-forest fragments in Western Ghats, India

The effects of fragmentation and overstorey tree diversity on tree
regeneration were assessed in tropical rain forests of the Western Ghats,
India. Ninety plots were sampled for saplings (1–5 cm diameter at breast
height (dbh); 5×5-m plots) and overstorey trees (>9.55 cm dbh;
20×20-m plots) within two fragments (32 ha and 18 ha) and two continuous
forests. We tested the hypotheses that fragmentation and expected
seed-dispersal declines (1) reduce sapling densities and species richness
of all species and old-growth species, and increase recruitment of
early-successional species, (2) reduce the prevalence of dispersed
recruits and (3) increase influence of local overstorey on sapling
densities and richness. Continuous forests and fragments had similar
sapling densities and species richness overall, but density and richness
of old-growth species declined by 62% and 48%, respectively, in fragments.
Fragments had 39% lower densities and 24% lower richness of immigrant
saplings (presumed dispersed into sites as conspecific adults were absent
nearby), and immigrant densities of old-growth bird-dispersed species
declined by 79%. Sapling species richness (overall and old-growth)
increased with overstorey species richness in fragments, but was unrelated
to overstorey richness in continuous forests. Our results show that while
forest fragments retain significant sapling diversity, losses of immigrant
recruits and increased overstorey influence strengthen barriers to natural
regeneration of old-growth tropical rain forests.