Rainforest Fires, Human Disturbance, and Vegetation History

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Large tracts of rainforests in Central and South America have been considered "virgin," the products almost entirely of natural processes. Significant human impacts on rainforests are thought by many to have been recent occurrences. Paleoecological and archeological research is providing new evidence that substantial human modifications of forested areas already may have been taking place in centuries before Europeans settled in the Western Hemisphere. This project will continue research on pre-Columbian forest modification already underway in and near the Le Selva Biological Station in northern Costa Rica. Pollen grains, charcoal fragments, and diatoms in sediment cores taken from lakes and swamps will be analyzed and used to reconstruct histories of natural vegetation, agricultural plants, and fires in the area. Among the research questions to be answered in this project are: How frequent were fires in Pre-Columbian forests? What crops and weeds associated with farming activity are found in the pollen record, and how does the presence of those crops and weeds relate to records of fires in the charcoal record? How frequently were forests cleared? Can climatic shifts be distinguished in the pollen and diatom records? This project will contribute new understandings related to the specific questions listed above and to many other related inquiries. Because similar types of inquiries are underway at other sites in Latin America, the results of this project also will contribute to comparative research aimed at identifying the nature and processes associated with human and environmental change on a continental scale. Methodological advances also will be made, especially the refinement of a new procedure for automated image analysis to identify charcoal fragments. Finally, the involvement of graduate and undergraduate students as members of the research team will provide excellent opportunities for their education, and collaboration with Costa Rican investigators should stimulate scientific development in that nation.