A multi-proxy reconstruction of the late Holocene vegetation dynamics in Krabi mangroves, Thailand Andaman Sea

Abstract

Pollen, charcoal, loss on ignition, geochemistry, and geophysical analyses were used to reveal the palaeoenvironment, vegetation, and sedimentary dynamics of the Krabi mangroves and the Andaman coast during the late Holocene. Two sediment cores, radiocarbon dated to ∼4400 cal BP, were collected from the Nai Nang mangroves in Krabi Province, the Thailand Andaman coast. This analysis documented how the area evolved from a tidal channel to a tidal area dominated by mangrove ecosystems. During the tidal channel phase (∼4400–2700 cal yr BP), the study site was characterized by a high-energy depositional environment, where sediment accumulated along tidal channels. Mangrove development began around 4400 cal yr BP and was influenced by varying contributions from tidal and freshwater inputs. Sea level during this period showed a slight rise until ∼4200 cal yr BP, followed by a subsequent fall. From ∼2700 to 1050 cal yr BP, the tidal channel was filled with finer sediments, forming intertidal flats that supported mangroves, back mangroves, and freshwater forest taxa, indicating a transition to mixed coastal vegetation. Sea levels remained relatively low during this period. From around 1050 cal yr BP to the present, mangroves replaced the previous mixed coastal vegetation, most likely driven by rising sea levels, particularly during the last 200 years. The observed sedimentation rates indicate that mangroves in Krabi will need to undergo continued future landward migration to adapt to changing coastal conditions, given the current and projected global sea-level rise.