Postglacial landscape dynamics and fire regimes in west Central Patagonia, Chile (44°S, 72°W): Evidence from the Cisnes River Basin

Abstract

We examine the long-term changes in vegetation structure and wildfires regimes in the Chilean Patagonia (44°S, 72°W) at the westernmost part of the Cisnes River basin. Previous studies within this basin have accounted for millennial shifts in glacier, vegetation and fire dynamics but at its easternmost portion. Here, we present a pollena macro-charcoal particles record from Laguna Las Mellizas del Río Cisnes (LLMRC; 44°38’48.13"S; 72°19’42.58"W; 209 m a.s.l.) that encompasses the last 13,900 cal yr BP. After glacier retreat, the LLMRC record shows incipient plant colonization upon the retreat of the ice caps (13,900–12,400 cal yr BP), inferred by the low PAR values (< 500 grains cm –2 yr –1 ) and negligible fire activity. The end of the Lateglacial period is characterized by increased values of N. dombeyi-type and the mistletoe Misodendrum, with the coeval presence ofPodocarpus nubigenus and Pilgerodendron uviferum suggesting humid and warm conditions since 12,400 cal yr BP. A peak in Weinmannia trichosperma percentages (~56%) marks the Holocene onset in the LLMRC record indicating a shift towards warmer conditions and enhanced rainfall seasonality, coupled with enhanced fire activity between 11,700 and 9000 cal yr BP. Increased moisture conditions after 9000 cal yr BP trigger the development of a closed Nothofagus-Podocarpus forest while the establishment of the North Patagonian rainforest occured during the middle Holocene (~8000 cal yr BP). The LLMRC record indicate a shift towards an open forest and moderate fire activity during the late Holocene. Despite the documented presence of indigenous population in the region, the results suggest no influence of human activity as potential triggers for fires in this record for the last 4000 years. Overall, the results of LLMRC record suggest the paramount importance of the Southern Westerlies in modulating the observed shifts in vegetation structure and wildfires at the westernmost portion of the Cisnes River basin.