Regeneration Mode in Neotropical Piper: Habitat and Species Comparisons

Abstract

Clonal growth or vegetative propagation is widespread among plants, yet we still have no clear understanding of the circumstances under which it is favored over sexual reproduction (via seeds). Within some growth forms of rainforest plants (lianas, understory shrubs), vegetative propagation may be the primary means of regeneration. In this study, the mode and frequency of vegetative propagation in 30 co—occurring species of the tropical shrub genus Piper at the La Selva Biological Station in Costa Rica was assessed through field observations made over several months. Piper species were found to propagate by several means, including stem sprouting, root sprouting, layering, and fragmentation. The mode and frequency of propagation varied significantly among habitats and among species. Shade—tolerant Piper species typical and mid— and late—successional habitats regenerated primarily by vegetative means, especially layering and fragmentation, while shade—intolerant, early—successional species appeared to reproduce and disperse primarily by seed. These differences among Piper species in regeneration mode were due not only to environment, but also to a genetic component, as indicated by experiments investigating the importance of one means of vegetative propagation, fragmentation, to Piper species from different successional habitats. A shadehouse experiment showed that early successional species were less likely than late—successional species to regenerate from detached fragments, independent of light regime. This outcome was corroborated by a transplant experiment in forest understory and large gaps comparing fragment vs. seedling survival among five Piper species from different stages of succession over a 7—mo period. Almost none of the cuttings from early—successional species survived in either habitat. Species of later successional stages survived better as fragments in the understory than in gaps; however, surviving fragments grew larger in gaps. Almost no seedlings from experimentally planted seeds of any species survived in either gaps or understory. Natural seedlings of early—successional Piper species were frequently found in large treefall gaps and other disturbances, while seedlings of species from late succession were seldom found in any habitat.