Southward migration of the austral limit of mangroves in South America
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Temperature influences the global distribution of mangroves, and global warming may be causing a poleward mangrove expansion. Sedimentary features, pollen, and isotopes data from six sediment cores, as well as 14C datings, indicated a marine transgression during the Holocene, and it contributed to the expansion of tidal flats occupied by saltmarshes. Environmental conditions suitable for mangroves development occurred on the study site during the Holocene, but, according to 210Pb and 14C dating, the establishment of mangroves mainly represented by Laguncularia trees only began between ~1957 and ~1986 (AD) on the studied tidal flats. Spatial-temporal analysis, based on satellite and drone images, revealed a mangrove expansion of ~10 ha in the study area between 2003 (96.1 ha) and 2019 (106.1 ha). Nowadays, in the study area, saltmarshes, mainly characterized by Spartina and Acrostichum, are sharing tidal flats with mangroves, represented by Laguncularia (≤5 m tall) and Avicennia (≤11 m tall). Probably, the absence of mangroves during the Holocene, followed by their establishment and expansion during the Anthropocene in the subtropical zone, is associated with a migration of the austral mangrove limit into the temperate zone, caused by the gradual increase in winter temperatures. This process may be related to a poleward mangrove migration since the late Holocene, caused by a natural Holocene global warming. However, the industrial-era warming must have intensified the mangrove expansion into temperate zones.