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“处女地”，几乎完全是自然过程的产物。许多人认为，人类对雨林的重大影响是最近才发生的。古生态学和考古学研究提供了新的证据，证明在欧洲人定居西半球之前的几个世纪，人类对森林地区的实质性改变可能已经发生了。该项目将继续在哥斯达黎加北部的勒塞尔瓦生物站及其附近进行的关于前哥伦布时期森林改造的研究。从湖泊和沼泽提取的沉积物岩心中的花粉粒、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。在这个项目中需要回答的研究问题包括：前哥伦比亚森林火灾的频率有多高？在花粉记录中发现了哪些与农业活动相关的作物和杂草，这些作物和杂草的存在与木炭记录中的火灾记录有什么关系？森林被砍伐的频率有多高？气候变化能从花粉和硅藻记录中区分出来吗？这个项目将有助于对上述具体问题和许多其他相关问题的新理解。由于在拉丁美洲的其他地点正在进行类似的调查，这个项目的结果也将有助于比较性研究，目的是在大陆范围内查明与人类和环境变化有关的性质和过程。方法学也将取得进展，特别是改进一种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小组成员的参与将为他们的教育提供极好的机会，并且与哥斯达黎加研究人员的合作应该刺激该国的科学发展。

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.