Title

Dynamics of woody seedling and sapling recruitment in second-growth tropical wet forests: An experimental approach

Date of Completion

January 2000

Keywords

Biology, Botany|Biology, Ecology|Agriculture, Forestry and Wildlife

Degree

Ph.D.

Abstract

To understand how biotic and environmental factors interact to influence woody seedling recruitment during secondary succession, I conducted two experimental studies in 15–20 year-old tropical forest stands. In one study, four manipulations of vegetation cover were applied in four secondary forest stands: large gap, small gap, one-time removal of the understory vegetation under an intact canopy, and control. Woody seedling and sapling recruitment and mortality were monitored for 2.5 years. I found a dramatic increase in abundance and diversity of woody seedlings in response to experimental gaps due partly to preferential recruitment of high-light demanding species that are common in the canopy but scarce or absent in the understory of unmanipulated stands. Light availability did not fully account for this increased recruitment. I also found contrasting patterns of early vs. late mortality between seedlings and saplings of tree vs. understory species. ^ The second study was a factorial experiment involving periodic manipulations of leaf litter cover and periodic clipping of understory vegetation in five plots containing a large artificial canopy gap and in five plots where the canopy was left intact. Woody seedling recruitment and mortality were monitored for 14 months. Gap treatment had an overriding effect on abundance, species richness and composition of recruited woody seedlings. Recruited seedlings of tree (but not understory) species showed contrasting recruitment responses to litter manipulations between gap treatments. These contrasting responses may be related to differences in seed size and germination requirements between tree species that recruited preferentially in gap vs. non-gap treatments. I also found contrasting patterns of mortality between tree and understory species and between initial and recruited seedlings in response to clipping and/or litter manipulations in gap vs. non-gap treatments. These results strongly suggest that biotic and abiotic factors interact in complex ways to influence abundance, species richness and composition of woody seedlings through differential effects on establishment and mortality. ^ I discuss the role of gap formation, understory vegetation and leaf litter cover in tree regeneration during secondary tropical forest succession, and the implications of these findings to forest management. ^