Late-Holocene vegetation dynamics and disturbance regimes in north Patagonia Argentina (40°S)

Abstract

Natural disturbance processes such as volcanic eruptions, fire and human activities are important vegetation drivers in north Patagonia. Here, we tested the impact of volcanic ash fall and fire on vegetation composition analysing two sediment records, Lake Avutarda and Lake Bruja, located in the forest-steppe transition at 40°S. In addition, our analysis provides the first account on the history of Nothofagus alpina at its eastern distribution limits. Our results comprise the last 3000 years, indicating the persistence of the vegetation despite evident volcanic activity documented by numerous tephra layers in both records. Eleven fire episodes were identified, while redundancy analysis indicates a non-significant influence of fire activity on the vegetation. The population increase of Nothofagus alpina represents the most important change in vegetation composition in the last three millennia. We speculate that the presumed change in climate, which led to the expansion of Austrocedrus chilensis south of the study area, also caused the increase of Nothofagus alpina populations in the region.

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

“…In palynological records, the abundance of N. dombeyi type is always variable, and few studies have assessed directly the responses to volcanic events. Álvarez‐Barra et al ( 2020 ) demonstrated that well‐developed forests were not affected in the long term by tephra fall smaller than 20 cm. However, after the large eruption of So‐A, the pollen abundance of N. dombeyi ‐type was strongly affected (this study and Dickson et al, 2020 ).…”

Holocene changes in forest composition in northern Patagonia responded to climate with little impact of disturbance

“…Likewise, Jara and Moreno (2012) associate major increases in Eucryphia/ Caldcluvia trees with tephra fall (Lake Pichilafqu en, 41 S). In contrast, Jara et al (2019) document that changes in the Southern Westerlies (SW) were the dominant driver of vegetation change rather than disturbance (Lago Espejo, 43 S) Studies on the impact of ash deposition on vegetation have been conducted also east of the main mountain chain ( Alvarez-Barra et al, 2020;Moreno-Gonz alez, 2020), showing negligible impact of ash deposition on the vegetation composition.…”

“…Studies also examined the spatial growth patterns (Donoso, 1988;Donoso et al, 1993;Echeverría and Lara, 2004;Puntieri et al, 2006;Sabatier et al, 2011) and site index models to quantify the productivity of a determined area with silvicultural purposes (Attis et al, 2015;Trincado et al, 2002). Unfortunately, few palynological records show the Nothofagus obliqua pollen type, which comprises pollen grains from N. obliqua and N. alpina ( Alvarez-Barra et al, 2020;Markgraf et al, 2009;Nanavati et al, 2020), and yet, little is reported on their Holocene history within their distribution range in northern Patagonian Argentina.…”