Lake-Sediment Records of Holocene Droughts, Indigenous Agriculture, and Prehispanic Vegetation and Fire Regimes in Northwestern Costa Rica

湖泊和湿地沉积物剖面的地层分析为理解人类与自然环境之间的长期相互作用提供了关键数据。本研究项目主要对哥斯达黎加西北部瓜纳卡斯特山脉米拉瓦莱斯火山下太平洋季节性干旱斜坡上六个湖泊的湖泊沉积物记录进行了开发、解释和评价。沉积物岩心已经从湖泊中恢复，这些湖泊形成于8000年前，与火山喷发的熔岩和泥流有关。研究人员将分析沉积物地层、宏观和微观木炭、花粉和硅藻组合，以记录全新世的气候、植被和火灾状况。他们还将记录湖盆内外史前和历史上人类对景观的改变，包括玉米种植开始和传播的时间。研究人员将根据现代植物物种分布、现代花粉和硅藻组合以及当地和区域考古学的信息来解释湖泊沉积物记录，以重建单个湖泊和流域的环境历史。每个湖泊的重建将相互比较，并与哥斯达黎加和中美洲其他地方的环境历史的古生态记录进行比较。这些比较将使研究人员能够区分自然和人类引起的环境变化的信号，评估环境和人类影响历史的空间变异性程度，并探索气候和文化历史之间可能的联系。这项研究的一个关键目标是确定湖泊沉积物记录是否保存了中美洲北部有记录的全新世晚期干旱的证据，如果是的话，如何比较这些干旱事件的时间、生态和人类影响。该项目应该有助于检验，例如，全新世气候变化是否对哥斯达黎加西北部的文化发展产生了重大影响，就像人们认为尤卡坦地区的情况一样。这项研究的另一个目的是为目前旨在恢复近几个世纪以来因农业发展而退化的热带干旱森林生态系统的土地管理计划提供历史背景。这种努力的重点是将火灾排除作为使森林恢复到干扰前条件的主要手段，但缺乏可能证明（或迅速修订）这种管理方法的火灾和植被的长期记录。过去的气候动态是现在和未来的关键。过去的自然气候变化影响了自然系统和人类系统，未来人类引起的气候变化也将如此。热带气候动力学对全球动力学的基本认识至关重要，但对其本身的了解仍然很少。该项目将提高对热带气候和生态系统历史以及自然环境变化和变异与人类文化之间关系的科学认识。研究结果还将有助于为哥斯达黎加西北部目前的土地管理提供信息。在这个项目中进行的研究将为几名研究生和本科生以及一名K-12教师提供教育机会，他们将参与该项目的实地工作。

Stratigraphic analyses of sediment profiles from lakes and wetlands provide key data for understanding long-term interactions between humans and the natural environment. This research project focuses on the development, interpretation, and evaluation of lake-sediment records from six lakes on the seasonally dry lower Pacific slope of Volcan Miravalles in the Cordillera de Guanacaste of northwestern Costa Rica. Sediment cores have already been recovered from the lakes, which formed as long ago as 8,000 years in association with lava and lahar flows from the volcano. The researchers will analyze sediment stratigraphy, macroscopic and microscopic charcoal, and pollen and diatom assemblages to document Holocene climate, vegetation, and fire regimes. They also will document prehistoric and historic human landscape modifications within and surrounding the lake basins, including the timing of the initiation and spread of maize cultivation. The researchers will interpret lake-sediment records in light of information on modern plant species distributions, modern pollen and diatom assemblages, and local and regional archaeology to reconstruct the environmental histories of individual lakes and watersheds. Reconstructions from each lake will be compared with each other and with paleoecological records of environmental history from other sites in Costa Rica and elsewhere in Central America. These comparisons will enable to researchers to differentiate among signals of natural vs. human-induced environmental change, to assess the degree of spatial variability in the histories of environments and human impacts, and to explore possible links between climate and cultural history. A key objective of the research is to determine whether the lake-sediment records preserve evidence of the late Holocene droughts documented in northern Central America, and if so, how the timing and ecological and human impacts of these drought episodes compare. The project should help examine, for example, whether Holocene climate change had a major impact on cultural development in northwestern Costa Rica, as is believed to have been the case in the Yucatan region. Another objective of the research is to provide historical context for current land-management plans aimed at restoring tropical dry forest ecosystems degraded by agricultural development in recent centuries. Such efforts focus on fire exclusion as a primary means to restore forests to pre-disturbance conditions, but long-term records of fire and vegetation that might justify (or prompt revision) of this management approach are lacking.Past climate dynamics are the key to the present and future. Natural climate variation of the past affected natural and human systems as will future human-induced climate change. Tropical climate dynamics are crucial to basic understanding of global dynamics, yet they remain poorly understood themselves. This project will improve scientific knowledge of tropical climate and ecosystem history and of relationships between natural environmental change and variability and human culture. The results will also help to inform current land management in northwestern Costa Rica. The research undertaken in this project will provide educational opportunities for several graduate and undergraduate students and for a K-12 teacher who will participate in the project's field work.