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.

Vegetation responses to past volcanic disturbances at the Araucaria araucana forest-steppe ecotone in northern Patagonia

“…A recent pollen record from Lake Cilantro (Dickson et al, 2020) shows similar patterns as those observed in Lake Relem, neither changes in pollen relative abundance after small tephra layers nor changes in PAR after So-A eruption. Although not a generalised pattern, Dickson et al (2020), Moreno-Gonzalez et al (2021 and Nanavati et al, (2020) showed that pollen abundance in areas nearby the current ecotone have been slightly increasing for the last˜4 ka despite of the influence of several volcanic eruptions. Further palaeoecological studies need to be done to understand the role of past volcanic eruptions in determining current diversity patterns in Araucaria forest and that can be used in the conservation of certain threatened species in the Valdivian Temperate Rainforest hotspot.…”

Disentangling the last 1,000 years of human–environment interactions along the eastern side of the southern Andes (34–52°S lat.)

“…The pollen and charcoal data from Laguna Portezuelo indicate the presence of an open, forest–steppe ecotonal landscape and steady fire activity through much of the Holocene ( Fig. 3 B ) ( 15 ). Rising pollen percentages of Nothofagus after 6590 cal y BP suggest more forest cover and increased moisture in the late Holocene.…”

“…We suggest that fire activity after ∼1580 CE (370 cal y BP) was amplified by climate-driven increases in fuel load during the LIA and in anthropogenic ignitions. A. araucana was of great cultural and resource significance to Mapuche and Pehuenche peoples ( 53 ), and evidence of its increase and more fires after ∼1580 CE (370 cal y BP) suggests local silvicultural management through deliberate burning ( 15 ). Tree-ring records near Laguna Portezuelo also indicate frequent fires at ∼6-y intervals during Mapuche–Pehuenche occupation ( 57 ).…”

Vegetation responses to past volcanic disturbances at the Araucaria araucana forest‐steppe ecotone in northern Patagonia

“…The authors recorded neither changes in pollen relative abundance after small tephra layers nor changes in PAR after So‐A eruption. Instead, Dickson et al ( 2020 ), Moreno‐Gonzalez et al ( 2021 ), and Nanavati et al ( 2020 ) showed that pollen abundance in areas near the current ecotone has been slightly increasing for the last ~4 ka despite the influence of several volcanic eruptions. Further palaeoecological studies need to be done to understand the role of past volcanic eruptions in determining current diversity patterns in Araucaria forest and that can be used in the conservation of certain threatened species in the Valdivian Temperate Rainforest hotspot.…”