Plant establishment on flooded and unflooded patches of a freshwater swamp forest in southeastern Brazil

Plant establishment was studied in a swamp forest in the lowland Atlantic rainforest in southeastern Brazil. A topographic gradient allowed a clear distinction between a periodically flooded and a permanently flooded site in the study area. Both sites were mosaics of patches: the former showed soil patches of varying sizes subject to distinct flooding durations (from 0 to 300 d per year) and in the latter, the tank bromeliads which densely occupied the understorey, trap litter and provided ‘suspended soil’ patches. In the periodically flooded site, the occurrence of regenerants (< 1.0 m tall) of the actively regenerating tree populations of Calophyllum brasiliense, Symphonia globulifera and Tovomitopsis paniculata (all Clusiaceae), originating from seed or vegetative organs, was recorded for 1 m2 quadrats placed in flooded (n = 82) and unflooded (n = 103) patches. In the permanently flooded site, dominated by Tabebuia cassinoides (Bignoniaceae), the presence of germinated seedlings was counted for 400 rosettes of the terrestrial tank bromeliad Nidularium procerum. The results showed that unflooded patches, including tank bromeliads, favoured seedling establishment. However, T. paniculata and T. cassinoides colonize patches where flooding lasts longer or is permanent mostly by reproducing vegetatively, while the seeds of C. brasiliense, which showed no form of vegetative reproduction, and S. globulifera are successful in colonizing flooded patches. Germination tests and field observations indicated that, for C. brasiliense, pre- and post-dispersal seed dormancy, a two-phase seed dispersal (water and bats) and seedling tolerance to flooding accounted for this pattern.