Environmentally induced clonal reproduction and life history traits of the liana Machaerium cuspidatum in an Amazonian rain forest, Ecuador
The population structure of the canopy liana Machaerium cuspidatum Kuhlm. & Hoehne (Fabaceae) was studied in ten transects covering a total of 2.5 ha of tropical rain forest in Yasuni National Park, eastern Ecuador. The aim was to investigate how trellis availability, topographic position and light availability affected the population density and structure of the most abundant liana species in the area. The environmental variation affected plants in different size classes differently. Large plants (diameter greater than or equal to1 cm) were almost exclusively found in areas with low canopy and dense undergrowth. These areas had the highest density of suitable host plants. Seedling-sized plants (height < 30 cm) and saplings (height &GE;30 cm but diameter < 1 cm) occurred more frequently and with higher density in steep upland areas than in the floodplains, presumably due to elevated seedling mortality in the periodically flooded areas. Seedling-sized plants and saplings did not grow in areas with elevated light levels, and although plants of all sizes were highly clumped, this clumping rarely coincided with patches with abundant canopy gaps. Machaerium cuspidatum reproduces clonally when branches re-root and break off from the parent plant. The density of clonally produced plants was high in areas where the density of sexually produced plants was low, whereas the total density varied little among habitat types. A higher proportion of the seedling-sized plants were of sexual origin in the upland areas. An environmentally induced increase in the production of independent ramets enables M. cuspidatum to persist in the floodplains. This shows that plants may expand their realised niches to habitats with a low potential for seedling survival if high seedling mortality can be compensated for by increased clonal reproduction.