Abstract/Summary

Understanding how Amazonian forest ecotones responded to past climate change and pre-Columbian land-use remains an important scientific challenge. Lake fossil pollen records are the main palaeoecological tool used to investigate these subjects in Amazonia. However, the method is limited in terms of its course spatial resolution and its application is constrained to regions with suitably aged lakes. This thesis explores the potential of soil-based palaeoecological proxies- phytoliths, stable carbon isotopes (δ13C) and macro charcoal- as methods to circumvent the spatial limitations of lake fossil pollen and to provide more spatially fine examinations of mid-Holocene ecotonal dynamics and pre-Columbian land-use. Chapter one introduces the project and Chapter two reviews the literature on Amazonian palaeoecology. Chapter three tests the sensitivity of soil phytoliths and δ13C analyses to capture local-scale, climatically driven shifts from different tropical forest ecotones from across Amazonian Bolivia. The proxies capture the resilience of dry forest-savannah ecotones to drought and fire over the Holocene at remarkably close distances to the modern boundary, i.e., 500m, indicating edaphic controls. However, soil proxies are found to be insensitive to climate driven rainforest-dry forest shifts, due to their low taxonomic resolution. When compared to lake pollen records, soil proxy signals at rainforest-savannah boundaries most-likely indicate the replacement of rainforest by dry forest or savannah in response to mid-Holocene drought. Chapter four examines the ability of off-site soil phytoliths to reconstruct pre-Columbian land use by examining new and previously published results. Soil phytoliths can detect the pre-Columbian enrichment of forests with palm on relatively short transects but have a limited ability to capture small-scale pre-Columbian cultivation and deforestation. However, when integrated with charcoal and archaeological data, the method can provide novel insights into pre-Columbian land-use.