Seed Ecology of Selected Amazon Basin Successional Species

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Abstract
Two adjacent forest sites (a mixed forest on well-drained Oxisols and a caatinga forest on water-logged Spodosols) were similar in the number of viable seeds m-2 in the seed bank: 180 for the mixed-forest site, 200 for the caatinga site. Most germinated seeds were of successional pioneer tree species. Seeds were entering the mixed-forest seed bank at a rate of .apprx. 50 seeds m-2 yr-1. Agricultural and pasture sites tended to have larger seed banks (580-1250 viable seeds m-2) composed almost entirely of grasses and forbs. The most common grass, forb, shrub and pioneer tree species in the forest and disturbed-site seed banks (8 spp. in all) were tested for their ability to persist for 1 yr in open storage cans on the forest floor and for their response to a variety of germination triggers. Seeds of all species tested were still alive after 1 yr of incubation on the forest floor. In a lighted environment these species showed good germination under both moist and flooded conditions, but neither daily temperature fluctuations nor the addition of nitrogenous compounds could induce germination in the dark. Hence, by coupling an absolute light requirement for germination with long-lived seeds, successional species of the upper Rio Negro region [Venezuela] are able to persist in the soil seed bank until conditions favor their successful establishment.