The ecology of conifer persistence in tropical rainforests: Podocarpus neriifolius in northern Thailand

A range of hypotheses seek to explain why conifers are infrequent in tropical rainforests. Here, we explore how the conifer, Podocarpus neriifolius , persists at low density in tropical lower montane rainforests of northern Thailand. Recruitment, growth and survival of seedlings and small saplings was monitored for 3.5 years in plots near and away from putative parent trees, and for large saplings and trees in a 16 ha forest plot over 8 years. Seeds and strobili were collected in litterfall traps for 2 years, and pollen rain extracted from forest floor moss samples. Demographic rates and ecophysiological traits of saplings were compared with co-occurring angiosperms Castanopsis acuminatissima and Calophyllum polyanthum . Survivorship was higher in the conifer for all size classes > 30 cm ht (0.97–0.99 y −1 vs. 0.92–0.98). Growth rate was similar for small saplings (9.3–12.6 cm y −1 ht), higher in P. neriifolius for large saplings (0.21 cm y −1 dbh vs. 0.11–0.12), but lower for trees (0.10 cm y −1 vs. 0.16–0.45). Canopy openness above saplings was similar amongst species (3.2–4.2%), whilst leaf N was lower (1.33% vs. 1.43–1.49%), and mass leaf per area (1.96 vs. 1.88) and δ13C higher (− 33.4 ‰ vs. – 34 to 34.9‰) for P. neriifolius. Pollen rain varied between plots, as did strobilus and seed fall between both plots and years, with highest pollen density, strobilus and seed fall close to parent trees, as were areas with highest seedling density and recruitment. High survivorship, high recruitment near parent trees and more widespread recruitment in mast years, offsets slower growth to ensure population persistence of P. neriifolius in angiosperm-dominated rainforest. Low stand density and patchy distribution is best explained by pollen limitation on seed production, with strong recruitment only where male and female trees occur in close proximity, and in mast seed years.