Determinants of fern and angiosperm herb community structure in lower montane rainforest in Indonesia

Abstract

Questions: Do ferns, which are physiologically less well adapted to conserve water than angiosperms but have more efficient propagule dispersal, show different vegetation–environment relationships than co-occurring angiosperm herbs? We hypothesized that ferns should show closer relationships to local environmental conditions and might be more closely associated with humid and shady microhabitats.

Location: Pono and Bariri, two sites in lower montane primary tropical forest, Lore Lindu National Park, Central Sulawesi, Indonesia.

Methods: At each site, all terrestrial herbaceous plants were sampled in 200 plots of 5 m × 5 m. Sixteen environmental factors describing soils, topography and canopy openness were recorded. Correlations were calculated to test the degree of similarity in the species richness and turnover of ferns and angiosperms, and their relationships with environmental factors. Species optima were calculated on each environmental axis and compared between plant groups via randomization tests.

Results: In total, 184 herb morphospecies were encountered at Pono and 135 at Bariri, of which almost 60% at each site were ferns. At both sites, fern species turnover showed closer correlations with soil variables than did angiosperm turnover. At the more topographically heterogeneous site (Bariri) fern species turnover was also more closely associated with topographic differences than was angiosperm turnover. Habitat preferences of ferns and angiosperms appeared more similar at Bariri than Pono, with both tending towards lower topographic positions and richer soils, but steeper slopes, than expected at random. At Bariri, neither plant group tended towards shady microsites, whereas at Pono ferns were better represented than angiosperms in microhabitats with open canopies.


Conclusions: As expected, ferns showed closer correlations with environmental factors than angiosperm herbs. Ferns did not, however, consistently favour humid microhabitats at both sites, and were not significantly associated with shady microhabitats at either site. Furthermore, it appears that physiological differences in water use do not lead to marked divergence in fern and angiosperm herb distributions in the humid understorey of this lower montane rainforest.