Pollen and charcoal from Tolhuaca National Park, south-central Chile

Aim: Few paleoenvironmental studies have been performed in
Araucaria-Nothofagus forests, which are highly vulnerable to ongoing
threats from climate change and anthropogenic activities. The primary goal
of this work is to reconstruct past environmental changes related to fire
disturbances over the last 1800 years in Tolhuaca National Park, Chile.
Location: Tolhuaca National Park, Araucanian region (38.2°S; 71.8°W),
Northwestern Patagonia, Chile. Taxa: Araucaria araucana (Araucariaceae),
Nothofagus spp. (Nothofagaceae). Methods: We completed charcoal and pollen
analyses to create two new paleoecological records that span 1800 years.
We compared the lake-based reconstruction with the available local
tree-ring fire scar chronologies from the last 430 years. Using these
data, we compute forest index changes, biomass burning trends, and compare
with estimates of archaeological radiocarbon density. We place our
inferences with context of published regional paleoclimatic proxies from
the Patagonian-Andean region. Results: Our results showed that fire
activity was higher than present between 200 and 1500 CE, with peaks
around 200-400 CE and 1100-1500 CE. Periods with high fire activity are
associated with reduced forest cover, as Araucaria declined when
mixed-severity fire regime occurred for extended periods. Pollen
assemblages suggested a shift from dry to wet climate conditions at 1500
CE, and from 1750 CE onward, the arrival of exotic species reflected the
land-use changes related to forest clearance and transhumance practices.
Main conclusions: The paleoenvironmental reconstructions showed changes in
vegetation, fire, and climate over the past 1800 years in TNP. Wildfires
have been the main disturbance process modifying the vegetation structure
in the Araucaria and Nothofagus forests. Since 1750 CE intensive
post-Hispanic land-use changes (forest clearances by fire and logging)
took place in the study area, reducing the native vegetation cover.
Climate variability, modulated by SAM-like and ENSO-like conditions,
influenced the fire activity (availability and flammability of fuels),
concomitantly with high archaeological density. The recent (after 2000 CE)
increase of catastrophic wildfires may negatively affect the conservation
strategies of Araucaria-Nothofagus forests.