Palaeoenvironmental changes over the last millennia in the subtropical forest of NW Argentina inferred fron fossil pollen records

LUPO L. C.; BRAUER A.; TORRES G. R.; CÓRDOBA F. E.; VIGNONI P. A.

Hamburgo

Conferencia; 25 Latin-American Colloquium of Geosciences; 2019

German Science Foundation

Recent research has provided evidence that many tropical and subtropical mountain plant species of South America are shifting their ranges upslope as a response to global warming. Some predictive models ensure that this trend will continue in the near future. Consequently, documenting the response of subtropical forests to present and past environmental changes is very useful in developing and validating vegetation models. Therefore, to have a greater degree of accuracy of these models, it is necessary to dispose of long-term studies. Currently, long-term specific data are scarce for the majority of subtropical tree species in South America. In order to contribute information about how the subtropical trees (e.g. Alnus acuminata, Polypepis australis, Podocarpus parlatorei, among others) of northwest Argentina responded to climate variability in the past, we have conducted a high-resolution analysis of a fossil pollen sequence in order to interpret the vegetation dynamics for the last millennium. We aimed to investigate the following topics: 1- Assess if the temperature is the unique parameter that induces vertical migration of the vegetation belts, 2- Distinguish vegetation responses to regional events (precipitation variability linked to the activity of South American Monsoon System). To achieve this, three sediment cores of different deep were extracted in Laguna Comedero (24º 06?S - 65º 29? W, 2035 m a.s.l.). Here we present the results of the reconstruction of vegetation based on pollen analysis that spans the last 1200 yr BP. The most important change in vegetation composition was observed ca. 1000 yr BP, when Poaceae pollen dominated indicating the expansion of the grassland by drier conditions or anthropic disturbance like deforestation. Later Alnus pollen appears as dominant until the present. Changes percentages in fossil pollen content, like increase in grasses, herbs and shrubs, could be related with a diverse degree of landscape handling, and/or dries periods, while increases of arboreal pollen can be attributed to more humid conditions (Alnus forest is related with up to 1000 mm/yr rainfalls, and the montane grassland with 600 mm/yr or less). Although, increases of the Alnus forest could be relatively more humid periods; this could also reflect moments of colonization in areas with strong environment disturbance (i.e. slipping). This evidence suggests that precipitation also could be a driver of the Alnus forest dynamics.