Seed viability as a function of moisture and temperature in the recalcitrant rainforest species Baccaurea ramiflora (Euphorbiaceae)

Context Fragmentation is a common and increasingly serious problem in tropical rainforests through the world, resulting in changes in species composition and subsequent species extinctions. Aim The aim of this study was to test the hypothesis that changes in species composition can originate from the different selection pressures on pioneer and climax seeds as the habitat changes. Methods Baccaurea ramiflora seeds were placed on the ground in six quadrats in five different habitats in the field, while graded temperature and relative humidity treatments in the laboratory were used to mimic the changed microclimate in rainforest fragments. Changes in seed moisture and viability were monitored. Results B. ramiflora seeds are recalcitrant and highly sensitive to both high temperatures and dehydration, with a reduced lifespan when temperature increased or relative humidity decreased, and viability is lost when dehydrated to 0.198 g/g or warmed to ≥ 35 °C. Germination was delayed in non-rainforest conditions compared with the rainforest understory, and only one-third of the seeds assigned to an open site germinated and emerged. Conclusion The results support our hypothesis that recalcitrant-seeded species have a high dependence on intact rainforests, and that fragmentation and disturbance will reduce their germination and establishment while favoring orthodox-seeded pioneers.