Shade and leaf loss affect establishment of grove-forming ectomycorrhizal rain forest tree species

The poor regeneration of Microberlinia bisulcata in groves in Korup, Central Africa was investigated in the forest to highlight factors that interact with light. Survival and growth of nursery-grown seedlings of M. bisulcata with four other species in each of two l-yr trials were recorded after transplantation into quadrats differing in PAR. Total mass was predicted for PAR treatments in nursery trials reported separately. Plant mass was strongly dependent on PAR for all species. At low PAR, across species, plant mass was positively related to seed mass. Forest : nursery mass ratios decreased with increasing PAR; M. bisulcata had the lowest ratios of all species at high PAR. Leaf weight ratio declined more steeply with increasing PAR in the forest than in the nursery and this was particularly marked for M. bisulcata. Herbivory was the most probable cause of leaf loss. Forest: nursery ratios were negatively correlated with species' abundances in the forest. Besides its small seed size and shade intolerance, M. bisulcata is highly susceptible to leaf loss when illuminated. Opportunities for seedling release are thus very low. (C) New Phytologist (2001) 151. 291-309.