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The main objective of the thesis is to provide a past-present-future perspective of climate changes and terrestrial ecosystem responses in South America. The first part investigates the vegetation response to a temperature increase from the Last Glacial Maximum (LGM) to the pre-industrial era. In order to verify the most affected biomes and explore how they might react to future warming it was employed the Center for Weather Forecasting and Climate Studies Potential Vegetation Model version 2 model (CPTEC PVM2). In addition, to determine the influence of each climate parameter on biome distribution, sensitivity experiments for both LGM and future scenario were run, considering the anomalies of CO2, precipitation and temperature separately. The results for the LGM indicate grassland expansion in southern Brazilian highlands and the persistence of the Amazon rainforest under colder and drier conditions. The western and central Amazon forest remained due to negative temperature anomalies, while a decrease in precipitation led to changes in the eastern portion. The reliability of computed precipitation anomalies and simulated potential vegetation for LGM is validated with compilation of 149 published vegetation and hydroclimate records. Results reaffirmed paleo studies that claim that changes in monsoon intensity cannot be used as the main driver for vegetational changes/stability across the Amazon biome, and that lower temperatures in combination with substantially lower CO2 are important controlling factors during the LGM. In contrast, for the future +4°C warming scenario, biome shifts will be driven by changes in precipitation. Savanna/Cerrado is projected to expand, while the Amazon forest, Tropical seasonal forest, and Caatinga may decrease. In the future warming scenario increasing temperatures with reduction in precipitation neutralize the potential gain in biomass from the positive effect of CO2 fertilization. The thesis also investigates the Atlantic Multidecadal Oscillation (AMO) as a potential main driver of warming/cooling scenarios and changes in precipitation in South America during the last millennium. This study evaluates AMO influence on atmospheric dynamics, precipitation and consequently {{δ18O}} of precipitation in South America using the water isotope-enabled version of the Community Earth System Model version 1.2 (iCESM1.2) forced with cold and warm AMO phase sea surface temperature fields. The model-derived AMO signal for the region under the influence of the Atlantic ITCZ aligns with proxy reconstructions, indicating changes in ITCZ during the Little Ice Age (LIA). One implication of these findings is that a change in the core strength of the ITCZ, caused by a persistent cold AMO, might have contributed to dry conditions over the northernmost part of South America and increased precipitation along the coastal area of northeastern Brazil during the LIA. Hydroclimatic spatiotemporal patterns during last millennium in other regions of South America remain puzzling. The study also warns that caution should be exercised when interpreting records reflecting annual means, as they may actually record signals of seasonal variability rather than ITCZ shifts. This thesis contributes to our understanding of past and future climate changes and terrestrial ecosystem responses in South America, highlighting the importance of considering both simulations and paleo records as neither available paleorecords nor state-ofthe- art models alone are conclusive, especially under extremely heterogeneous and complex environmental conditions.