Flood-tolerance and flood-escape mechanisms for seeds and seedlings of common swamp trees of Central America.
Tropical swamp forests are characterized by relatively low diversity of tree species which are often believed to be flood tolerant. However, the diverse habitats in which some "swamp" species, e.g. Calophyllum brasiliense, are found suggest that the trees may not be uniquely adapted to swamp living. I conducted a series of experiments on seeds and seedlings of common Central American (Costa Rica, Nicaragua, and Puerto Rico) swamp forest trees. In total, eleven species (Andira inermis, Annona glabra, Calophyllum brasiliense, Carapa guianensis, Grias cauliflora, Lonchocarpus costaricensis, Pachira aquatica, Posoqueria latifolia, Prioria copaifera, Raphia taedigera and Rhizophora mangle) were used in different germination and seedling survival experiments in Nicaragua. The refuge provided by Pterocarpus officinalis buttresses was explored in two short studies. Germination experiments in the field indicated that seeds of some swamp species (notably Calophyllum brasiliense, Carapa guianensis, and Prioria copaifera) did not germinate in standing water, and similarly did not survive six-week periods of submersion as seedlings. In a microtopography study, overall seedling densities were significantly higher in the elevated refuge provided by Pterocarpus buttresses. In the absence of adaptations to flooding, other mechanisms might be important in allowing the establishment and survival of tree species in swamps. Together, the results suggest that although flood tolerance is strong in some species, flood escape may be the method by which other common species establish in swamps. Key species like Calophyllum brasiliense, Carapa guianensis and Prioria copaifera are not flood tolerant but instead utilize a range of flood escape mechanisms to allow their existence in swamp forests.