CHRIS J. PETERSON, BRUCE L. HAINES, and JERALD J. DOSCH. submitted. Scarce evidence for Initial Floristic Composition or nucleation during early secondary succession in premontane southern Costa Rica . Biotropica, in review.

Abstract

Two of the most enduring hypotheses about secondary succession, Initial Floristic Composition (IFC), and nucleation, have rarely been tested in tropical systems. IFC posits that the eventual dominant species are present from the beginning of the successional period, but remain small or dormant during the early years. Nucleation suggests that isolated remnant trees are foci for new woody plant establishment, leading to greater colonist density beneath or near the remnant trees than away from them.

To test IFC, in June 2005, we sampled replicate quadrats for small woody colonists at several distances from forest edge in four successional abandoned pastures in southern Costa Rica. We found few woody seedlings (0.2 - 1.2 stems m-2), and among those present fewer than 8% were mature-forest tree species. Thus IFC does not describe the early stages of succession in these sites. To test nucleation, we utilized spatial maps of woody plants that have recruited between 1996 and 2005 in the four abandoned pastures. We selected 100 random points and counted the density of woody colonists, and compared these ‘random-point’ densities to colonist densities around isolated remnant trees. The density of woody colonists within 4 m of isolated remnant trees was in most cases not more than one standard deviation above the mean colonist density at the random points (away from remnant trees), demonstrating a very limited role for nucleation. We propose that the lack of evidence for IFC and nucleation in these pasture sites is due severe limitations on seed dispersal, and the fine-scale mosaic landscape, respectively.