Precipitation variability and disturbance regimes shaped temperate rainforests since ~7 ka in NW Patagonia (~42°S)

Abstract

We investigate temperate rainforest responses to climate and disturbance regimes since ~7 ka on the Andean foothills of the Estuario Reloncaví sector of the Chilean Lake District, using a decadally resolved record from Lago Campanario. Our results show mixed temperate rainforests with dominance of Valdivian Rainforest assemblages between ~6.8–3 ka followed by a gradual transition toward North Patagonian Rainforest-dominated assemblages from ~3 ka to the present. This trend is overprinted by centennial-scale fluctuations, most intensely developed between ~2–0.3 ka. We interpret relatively warm/dry conditions between ~6.8–5 ka followed by a multimillennial trend toward cool-temperate/humid conditions until the present. Large-magnitude hydroclimate changes at centennial timescale prevailed between ~2–0.3 ka, culminating with cool-temperate/humid conditions and subsequent Chilean/European disturbance. Fire activity was predominantly low and punctuated by discrete increases, the largest of which occurred between ~5.6–5.5 ka and ~1.4–0.6 ka. Tephra layers attest to explosive volcanism with multiple events clustered between ~6.2–6.1 ka, ~3.5–2.5 ka, and ~1.4–0.9 ka. Significant rates-of-change scores at ~5.7 ka, ~1.3 ka, and between ~0.7–0.3 ka document abrupt vegetation changes following fire episodes and explosive volcanic events. We interpret invigoration of the southern westerlies since ~7 ka overprinted by centennial-scale variability that promoted fires during warm/dry anomalies. Fires and explosive volcanism, aided by pre-Columbian (⩽1.4 ka) and historical human burning (⩽0.2 ka), catalyzed vegetation responses to climate change promoting the proliferation of fast-growth shade-intolerant taxa. Disturbance during relatively warm/dry intervals favored the rainforest trees Eucryphia/Caldcluvia and Weinmannia trichosperma, whereas cool-temperate/humid intervals favored Nothofagus and Poaceae.