Early Plant Succession in Abandoned Pastures in Ecuador1

We compared early plant succession in four abandoned pastures of differing age since abandonment and a nearby secondary forest site in northwestern Ecuador. Two “Open” pastures had no tree canopy covering, and two “Guava” pastures had a well-developed canopy cover of Psidium guajava. No site had been seeded with pasture grasses. All pastures were compared in a chronological sequence; two were monitored for 18 months. Species richness was consistently higher in Guava sites than in Open sites and it continued to increase over time, whereas it remained static in Open sites. Species richness was highest in secondary forest. Recruitment of tree saplings in Guava sites was lower than in secondary forest; however, it was nearly absent in Open sites. The seed bank contained predominantly herbaceous species at all sites, and was highly dissimilar to aboveground vegetation. Dominance-diversity curves for Guava sites showed a more equitable distribution of species that increased over time. In contrast, dominance-diversity curves for Open sites were static and indicated dominance by a few aggressive species. Soil characteristics among sites were variable; however, a principal components analysis on soils isolated the older Open site from all others. The older Open site had the lowest species richness and was dominated by Baccharis trinervis, an aggressive shrub species. The site appears to be in a state of arrested succession and some form of restorative intervention may be necessary to initiate succession toward a forested condition. Succession in Guava sites appears headed toward secondary forest, whereas it does not in Open sites.