Rainforest Fires, Human Disturbance, and Vegetation History

中美洲和南美洲的大片热带雨林被认为是“原始的”，几乎完全是自然过程的产物。许多人认为，人类对热带雨林的重大影响是最近发生的。古生态和考古研究正在提供新的证据，表明在欧洲人定居西半球之前的几个世纪里，人类可能已经对森林地区进行了实质性的修改。该项目将继续对哥斯达黎加北部Le Selva生物站及其附近已经在进行的前哥伦布时期的森林改造进行研究。从湖泊和沼泽中采集的沉积物岩心中的花粉颗粒、木炭碎片和硅藻将被分析并用于重建该地区的自然植被、农业植物和火灾的历史。在这个项目中要回答的研究问题包括：哥伦布以前的森林火灾的频率有多高？在花粉记录中发现了哪些与耕作活动有关的作物和杂草，这些作物和杂草的存在与木炭记录中的火灾记录有何关系？森林被砍伐的频率有多高？在花粉和硅藻记录中能区分气候变化吗？该项目将有助于对上述具体问题和许多其他相关问题有新的理解。由于拉丁美洲的其他地点也在进行类似类型的调查，该项目的结果也将有助于进行比较研究，以确定与大陆范围内的人类和环境变化有关的性质和过程。还将在方法学上取得进展，特别是改进用于自动图像分析以识别木炭碎片的新程序。最后，研究生和本科生作为研究团队成员的参与将为他们的教育提供极好的机会，与哥斯达黎加研究人员的合作将促进该国的科学发展。

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.