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

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

Hamburgo

Conferencia; 25 Latin-American Colloquium of Geosciences; 2019

Recent research has provided evidence that manytropical and subtropical mountain plant species of South America are shiftingtheir ranges upslope as a response to global warming. Some predictive modelsensure that this trend will continue in the near future. Consequently,documenting the response of subtropical forests to present and pastenvironmental changes is very useful in developing and validating vegetationmodels. Therefore, to have a greater degree of accuracy of these models, it isnecessary to dispose of long-term studies. Currently, long-term specific dataare scarce for the majority of subtropical tree species in South America. Inorder to contribute information about how the subtropical trees (e.g. Alnus acuminata, Polypepis australis, Podocarpusparlatorei, among others) of northwest Argentina responded to climatevariability in the past, we have conducted a high-resolution analysis of afossil pollen sequence in order to interpret the vegetation dynamics for thelast millennium. We aimed to investigate the following topics: 1- Assess if thetemperature is the unique parameter that induces vertical migration of thevegetation belts, 2- Distinguish vegetation responses to regional events(precipitation variability linked to the activity of South American MonsoonSystem). To achieve this, three sediment cores of different deep were extractedin Laguna Comedero (24º 06?S - 65º 29? W, 2035 m a.s.l.). Here we present theresults of the reconstruction of vegetation based on pollen analysis that spansthe last 1200 yr BP. The most important change in vegetation composition wasobserved ca. 1000 yr BP, when Poaceaepollen dominated indicating the expansion of the grassland by drier conditionsor anthropic disturbance like deforestation. Later Alnus pollen appears as dominant untilthe present. Changes percentages in fossil pollen content, like increase ingrasses, herbs and shrubs, could be related with a diverse degree of landscapehandling, and/or dries periods, while increases of arboreal pollen can be attributedto more humid conditions (Alnusforest is related with up to 1000 mm/yr rainfalls, and the montane grasslandwith 600 mm/yr or less). Although, increases of the Alnus forest couldbe relatively more humid periods; this could also reflect moments ofcolonization in areas with strong environment disturbance (i.e. slipping). Thisevidence suggests that precipitation also could be a driver of the Alnus forest dynamics.