Early successional patterns and potential facilitation of woody plant colonization by rotting logs in premontane Costa Rican pastures

We examined the size, species, location (x and y coordinates), and microsit e inhabited by colonizing trees and shrubs in five abandoned pastures in so uthern Costa Rica. All woody stems greater than I m tall in the pastures we re measured and mapped, from the overhanging forest edge to 50 m into the a bandoned pasture. Species composition of colonists differed substantially a mong pastures: Croton draco (Euphorbiaceae) dominated one site, two species of Miconia (Melastomataceae) another site, and Verbesina tapentiensis (Ast eraceae) a third site. Site 4 had the highest cover of rotting logs (11%), and a four-fold greater density of colonizing woody plants than the site wi th the next highest colonist density. For all species pooled, and for sever al individual taxa, density was positively correlated across sites with abu ndance of log microsites. Four of the six most common woody species in site 4 occurred on logs signif icantly more often than expected had they been randomly distributed relativ e to logs. Site 5 had less abundance of logs, but the common Miconia specie s was again significantly more likely to be found on log microsites. These results strongly suggest that rotting wood microsites facilitate establishm ent of bird-dispersed pioneer trees, which in turn could foster regrowth of other forest species.