Humans exacerbated wildfires in the NW Patagonian archipelagoes over the last 2700 years

Abstract

The onset of human-driven transformations of the landscape, and the functioning of terrestrial ecosystems before and after such onset, remain largely unconstrained in the temperate rainforest region of western Patagonia. Prominent channels and archipelagoes define a fragmented landscape where natural fire activity is rare owing to the hyperhumid, low-seasonality climate, considerable distance upwind from Andean eruptive centers, and sectors with negligible historical human disturbance. Here we examine the role of humans as past drivers of vegetation and fire-regime shifts with a fine-resolution, lake-sediment record from Lago Huillín, located on southern Isla Grande de Chiloé (∼43°S). This is an isolated, strategic sector for modern and ancient navigation throughout the western Patagonian channels located just north of the core of the mid-latitude westerlies. We find a tight coupling between vegetation, fire activity, and westerly wind influence between ∼17.9 and 2.7 ka (ka: 1000 years before present) followed by unprecedented fire maxima between ∼2.7 and 0.3 ka, decoupled from a temperate-hyperhumid regime with uninterrupted dominance of temperate rainforests. This extraordinary condition occurred in the context of enhanced precipitation variability and widespread human occupation over the Patagonian channels in an otherwise fire-suppressed setting, establishing an unambiguous human footprint in a region classically regarded as pristine.