A Holocene history of monkey puzzle tree (pehuén) in northernmost Patagonia

Abstract

Aim: Although it is established that climate and fire have greatly influenced the long-term ecosystem dynamics of Patagonia south of 40°S, the environmental history from northernmost Patagonia (37–40°S), where endemic and endangered monkey puzzle tree (Araucaria araucana) occurs, is poorly known. Here we ask: (a) What is the Holocene vegetation and fire history at the north-eastern extent of A. araucana forest? (b) How have climate and humans influenced the past distribution of A. araucana?. Location: Northernmost Patagonia, Argentina and Chile (37–40°S). Taxa: Araucaria araucana, Nothofagus, Poaceae. Methods: Sedimentary pollen and charcoal from Laguna Portezuelo (37.9°S, 71.0°W; 1,730 m; 11,100 BP) were evaluated using statistical methods and compared with other palaeoecological, independent palaeoclimate, and historical records to assess how changes in climate and land use influenced local-to-regional environmental history. Results: An open forest-steppe landscape persisted at L. Portezuelo throughout the Holocene with generally low-to-moderate fire activity. Increased Nothofagus pollen after ~6,590 BP suggests increases in shrubland and moisture in association with cooler conditions and greater seasonality and ENSO activity. Araucaria pollen appeared at L. Portezuelo at ~6,380 BP, but was low in abundance until ~370 BP, when it rose with charcoal levels. This increase in Araucaria and fire coincided with a regional influx of Mapuche American Indians. Nothofagus deforestation and Pinus silviculture marked Euro-American settlement beginning in the 19–20th century. Main conclusions: (a) Rapid postglacial warming and drying limited the distribution of Araucaria in the central valley of Chile. In the middle and late Holocene, decreased temperatures and greater seasonality and ENSO activity increased precipitation variability allowing Araucaria expansion at its north-eastern limit. (b) Greater abundance of Araucaria and heightened fire activity at L. Portezuelo after 370 BP coincided with increased Mapuche-Pehuenche American Indian land use, suggesting that Araucaria may have been managed in a human-altered landscape.