NSF Award Abstract - #0242286

AWSFL008-DS3

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

Abstract

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.