Collaborative Research: Causes and Consequences of Tree Colonization Patterns in Wet Tropical Forests

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In many tropical regions world-wide, forests are regrowing after abandoned agriculture or logging, but this process is poorly understood. This three-year study will examine the process by which canopy trees recolonize abandoned sites in wet, tropical forests that were initially cleared for agricultural use in the Atlantic lowlands of Costa Rica. To determine why certain species arrive and establish at different times during the forest recovery process, the investigators will compare: "young" sites, which have recently developed a closed forest canopy (5-10 years after abandonment); "intermediate" sites, which have a well-developed forest structure (19-32 yrs after abandonment); and "mature" sites, which have remained intact. Seeds of 12 canopy tree species will be planted to examine how different factors affect seedling survival across different stages of forest development. These factors include access to seed-eating animals, competition with existing seedlings, and the amount of light available near the forest floor. In addition, the investigators will establish and monitor plots in the three forest types and then census and map all canopy trees each year. In hundreds of mapped smaller plots, all seedlings of canopy tree species will be counted and tagged. The dispersion of seedlings relative to the locations of mature trees of the same species will be compared among tree species that exhibit different patterns of recolonization. To evaluate the role of light in the forest recovery process, the investigators will assess light levels for monitored seedlings and determine the relative importance of light and proximity to fruiting adults in explaining seedling dispersion patterns. Throughout the study, new arrivals, deaths, growth, and size distributions of canopy species will be monitored in ten one-ha plots. This research will help to guide forest recovery efforts in tropical regions, and provide training in the methods of forest mapping, monitoring, and data analysis.