Climate, sea-level, and anthropogenic influences on coastal vegetation of the southern Bahia, Northeastern Brazil, during the mid-late Holocene

Abstract

The Atlantic Forest and mangrove dynamics along the Brazilian coast have been affected by climate, relative sea-level (RSL), and anthropogenic forces. Individualizing the effects of these drivers on paleoecological records is a challenge. This was addressed by pollen analysis along three cores sampled from lakes on a coastal plateau, primarily influenced by rainfall, and from a fluvial valley, influenced by sea-level and fluvial discharge, in northeastern Brazil. Pollen records from the fluvial valley indicated the presence of mangroves along an estuary in the mid-Holocene. During the past ~5800 cal yr BP, mangroves, adapted to brackish water, were replaced by herbaceous vegetation adapted to freshwater in the fluvial valley. Concurrently (~5680–240 cal yr BP), expansion of Atlantic Forest and contraction of herbaceous vegetation occurred on the coastal plateau. This divergence of pollen records between two distinct sedimentary environments (lakes on a coastal plateau and fluvial valleys) was attributed to RSL and climate effects. The combination of RSL fall and higher fluvial discharge favored seaward mangrove migration and expansion of herbaceous vegetation along the fluvial valley during the mid-late Holocene. However, the increase in rainfall on the coastal plateau favored the expansion of arboreal vegetation and contraction of herbaceous vegetation. At ~1700 CE, an abrupt shift from arboreal to herbaceous vegetation occurred on the coastal plateau. This vegetation change is likely attributed to European colonization on the southern coast of the state of Bahia, which was colonized by Portuguese navigators ~1500 CE. Part of the Atlantic Forest has naturally regenerated and was preserved as a national park in recent decades. This study showed that although the sampling sites are close, pollen assemblages can differ considerably depending on the depositional environment. Therefore, pollen analyses in different depositional environments are necessary to assess individually driving forces impacts on coastal vegetation dynamics during the Holocene.