SHEENA S. HILLSTROM, CHRIS J. PETERSON, AND BRUCE L. HAINES. submitted. Rotting log microsites facilitate forest regeneration in abandoned pastures of southern Costa Rica. Restoration Ecology, in review.

Abstract

Because of intense competition with herbaceous vegetation at soil level, woody seedlings in tropical abandoned farmlands sometimes preferentially establish on rotting logs. However, the longer-term outcome (growth and survival) after such establishment is unknown. Here we compare fate and performance of woody seedlings growing on rotting logs to those growing on soil in three abandoned pastures in the premontane zone of southern Costa Rica, for the period 1998-2005. We also conducted a germination study using four species planted on log and soil microsites (open, grassy pasture) in 2006. For all sites and cohorts pooled, seedlings on logs had significantly better survival than seedlings on soil. Additional recruitment since 1998 has been significantly greater than expected on logs in one of the three sites. In 2005, woody colonists had significantly greater trunk diameter and height on logs than on soil, in all three sites (height corrected for diameter of logs). There was no significant difference in germination between log and soil microsites for four species in 2006. By 2005, 10.4%, 30.5%, and 39.9% of woody colonists were on log microsites in the three sites, despite these microsites covering only small percentages of the surface (11% and 3% in sites were logs were encountered in surface sampling). Similar growth and slightly better survival on rotting log microsites has maintained the strong concentration of woody plant colonists on logs in these abandoned pastures, suggesting that the initial facilitation by logs continues to enhance forest regeneration throughout the first decade..