AN APPLICATION OF PHYTOLITHS TO RECONSTRUCT MID- TO LATE HOLOCENE VEGETATION CHANGES IN RESPONSE TO CLIMATE CHANGE AND HUMAN SETTLEMENT IN NORTHCENTRAL PUERTO RICO

The inorganic nature of phytoliths, opal silica casts that allow taxonomic determinations of ancient vegetation assemblages, makes them an advantageous tool to study the effects of climate change and human land use in alluvial contexts where wet-dry cycles hinder the preservation of other proxies such as pollen and macrobotanical remains. Despite their already wide application in palaeoecological and archaeological studies around the globe and even in the Neotropics, few studies in the Caribbean have used this method to reconstruct past vegetation dynamics. This paper presents a reconstruction of palaeovegetation from four sedimentary sequences obtained through deep coring of alluvium and a cutbank exposure from the Rio Grande de Manatí (RGM), northcentral Puerto Rico. The RGM is one of the most extensively researched river catchments with archaeological sites spanning the entire temporal dimension of human settlement (~6,300 cal. BP) in the archipelago of Puerto Rico. Thus, the RGM provides a good case study to understand the long-term relationship between climate change, human land use, and local environments since the Mid- to Late Holocene. I reconstruct the processes of aggradation and pedogenesis that have shaped the lower catchment over the last >6,000 years through a suit of geochemical and geophysical techniques (e.g., grain size, TOC, magnetic susceptibility, and x-ray fluorescence). Then, I reconstruct vegetation assemblages using phytoliths and stable carbon isotopes from appropriate contexts (i.e., buried paleosols) to understand their spatial and temporal relationship to human presence in the catchment. I also present on the particular methodology used for phytolith recovery and taxonomic identifications with the aid of a reference collection from native species.