The Montane Atlantic Rainforest of Southeastern Brazil: altitudinal migration and microrefugia during the Late Pleistocene and Holocene

The Montane Atlantic Rainforest of southeastern Brazil is a unique ecosystem worldwide, as it is home to endemic and endangered species that are vulnerable to global warming. In order to contribute to the future preservation of this ecosystem, this study reconstructs the past vegetation of two mountain areas in the Southeast and its relation to the climatic changes of the Last Glacial Maximum (cooling) and Mid Holocene (warming). For these purposes, the following hypotheses were tested: a) migration of the Atlantic High-Montane Forest to the Serra do Mar region of São Paulo during the Last Glacial Maximum, ca. 22,000 calibrated years Before the Present (cal. years BP), b) altitudinal migration and formation of microrefugia with typical taxa of the Montane Atlantic Forest in response to rising temperatures during the Mid Holocene, ca. 6,000 cal. years BP, in Southeast Brazil. The testing of these hypotheses was carried out through palynological analysis, studies of modern pollen rain, analysis of organic geochemistry (C, N, C/N, δ13C, δ15N) in sediments from the Curucutu Nucleus of Serra do Mar State Park (SP), at 765 m elevation and at the Itatiaia National Park (MG / RJ), at 2386 m. The palynological results, at the Curucutu Nucleus, show the migration of Araucaria angustifolia to this region between 25,351 and 19,862 cal years BP suggesting the presence of mixed ombrophilous forest in sync with Campos de Altitude, in a forest/ high altitude savanna mosaic landscape. During the period of 11,473 and 3,987 cal years. BP, there is a significant increase in forest vegetation, confirming the altitudinal migration of montane taxa from adjacent regions and from the slopes of Serra do Mar to areas above 750 meters of altitude. The palynological results of the Itatiaia National Park validate the altitudinal migration to areas above 2,200 meters of altitude, with the formation of microrefugia. This process occurred gradually and continuously, starting at around 6,213 cal years. BP and lasted until 4,255 cal years BP. The palynological data also show that the Mid Holocene, of these two locations, was characterized by the presence of nuclei of microrefugia (capões) dispersed in high altitude savanna landscape, under humid and cold conditions while the lowlands experienced hot climates. Organic geochemical analyzes independently support the palynological results and confirm the presence of plants with a C3 photosynthetic cycle between 6,000 and 4,000 cal. years BP, suggesting the presence of humid herbvaceous and arboreal vegetation in both locations. Statistical analyzes together with the modern pollen rain data allowed the differentiation of vegetation types, as well as the identification of the main components controlling the pollen spectra in the two study areas and the position of the Itatiaia National Park tree line, contributing to the test of the paleoecological hypotheses proposed for the Last Glacial Maximum and Middle Holocene. (AU)