The Cecropia Seedbank in the Surinam Lowland Rain Forest

Abstract

The Cecropia seedbank (consisting of seeds of C. sciadophylia a:d C. obtusa) under pristine Surinam lowland rain forest has been studied from 1970 to 1978. The germination of Cecropia seeds is strongly induced by normal daylight; Cecropia seeds also show a moderate germination in darkness with fluctuating temperature (20-30?C). The Cecropia seedbank was sampled during a year at two-month intervals to a soil depth of 2 cm. The average total number of viable Cecropia seeds in the humus and 0-2 cm layer amounts to 73/m2. The quantity of Cecropia seeds sharply decreases with depth, and most viable Cecropia seeds germinated from the 0-1 cm soil layer. Closed earthenware pots containing seeds of C. sciadophylla and C. obtusa were buried at two sites (in mesoand xerophytic forest) and the seeds periodically tested for viability. Seeds of C. sciadophylla as well as C. obtusa were highly viable after 62 ard 48 months of storage, respectively, at the two sites. The results are discussed in relation to the natural germination conditions for Cecropia seed in the Surinam lowland rain forest. Possible germination trigger mechanisms for Cecropia seeds are normal daylight and fluctuating temperature. A review is given of the dispersal agents of Cecropia seed. Cecropia propagation is independent of specialized pollinators and dispersal agents; its opportunistic germination ecology enables the genus to exploit successfully natural openings and clearings in the rain forest. THE IMPACT OF MAN on the vegetation of tropical lowlands has frequently resulted in an explosive increase of a group o'f species generally called secondary species or nomads (Van Steenis 1958). Several authors (Guevara 1973, Gomez-Pompa et al. 1972, Gomez-Pormpa and Vazquez-Yanes 1974, VazquezYanes 1974) pointed out that autecological research on secondary species could delineate the adaptive characteristics which permit these species to colonize and exploit disturbed habitats. In many parts of the lowland neotropics Cecropia spp. are early colonizers after severe disturbances of pristine forest. Thus, after clear-cutting mass-germination may occur, often in the absence of nearby mature trees. As Cecropia spp. are fast growing, even-aged Cecropia stands develop within a few years. No Cecropioa regeneration occurs in these stands, neither initially nor when the trees produce seeds, after several years. Although the viable seed content of tropical soils has been les,s investigated in comparison to that of the temperate zones (Harper 1977), it has been known for some time that (forest) soils of tropical regions contain considerable amounts of viable seeds of secondary species (Symington 1933, Van Steenis 1941, Aubreville 1947). However, the buried viable seed population may play an important role as a source for plant colonists in the secondary succession in the tropics (Budowski 1961, 1965, 1970; GomezPompa et al. 1972; Guevara 1973). Recently, more attention has been paid to the quantitative aspects of the seedbanks, i.e., in Africa (Keay 1965), Southeast Asia (Liew 1973), and Middle America (Guevara and Gomez-Pompa 1972). As part of the seedbank in forest soils in Middle America, the Cecropia seedbank has been studied: qualitatively by Budowski (1961, 1965), who suggested that Cecropia seeds may possess the ability to remain dormant, and quantitatively by Bell (1970), Guevara and GomezPompa (1972), and Kellman (1974, 1978), the last