Abstract

Southwestern Patagonia (SWP, similar to 50 degrees-55 degrees S) is strategically located for monitoring the functioning of the climate system and terrestrial ecosystems in the southernmost continental landmass in the path of the Southern Westerly Winds. Here we report results from Lago Sindorito, a small closed-basin lake located on the eastern slopes of the SWP Andes to investigate past changes in vegetation, climate, and fire regimes since local ice-free conditions just upwind from the modern forest-steppe ecotone. We observe an abrupt Nothofagus rise at similar to 13.1 ka that led to forests which have persisted until recently despite interruptions and variations in structure and dynamics. Forest-dominated intervals (similar to 12.5-9 ka, similar to 6.4-0.1 ka) feature low rates-of-change scores (ROC), suggesting vegetation stability, in contrast to intervals dominated by scrubland (similar to 9-7.3 ka, similar to 0.1 ka-modern), which feature higher ROC implying dynamic and/or unstable states. Precipitation declines coupled with fire disturbance drove rapid deforestation and slope instabilities/erosion, associated with peak ROC. Transient and modest centennial-scale declines in Nothofagus occurred followed local fires, suggesting episodes of canopy opening/closure akin to forest patch dynamics at small spatial/temporal scales. The prevalence of Nothofagus-dominated forests since similar to 12.5 ka suggests temperate and humid conditions on the eastern slopes of the SWP Andes, implying permanent influence of the westerlies. This background condition was overprinted by diminished westerly wind influence at millennial and centennial timescales. Our results suggest an early Holocene (similar to 10.3-7.3 ka) westerly minimum, a Late Holocene westerly maximum (similar to 3-0.1 ka), and a historical decline concomitant with the onset of large-magnitude disturbance by Chilean/European settlers since the 19th century.