Palynological Study on Holocene Environmental Change with Special Reference to Responses of Peatlands and Mangroves, Indonesia

Holocene mangrove dynamics in the Makassar Strait and developmental history of peatland in Central Kalimantan were examined on the basis of pollen analysis, peat stratigraphy and radiocarbon dates. The results indicate that mangroves flourished on Kalimantan coast and on-site mangrove colonization occurred extensively on Sulawesi coast during Early-Mid Holocene due to sea-level transgression. These mangroves have degraded to some extent due to a high rate of sea level rise prior to the Holocene maximum transgression. Progradation occurred at Batulicin in Kalimantan and Pare-Pare in Sulawesi following the sea-level stabilization and sea-level regression. As a result, mangroves encroached and on-site mangrove colonization occurred at Batulicin in Kalimantan. In contrast, mangrove development was abruptly halted at Pare-pare in Sulawesi during the Mid-Holocene. Deposition since the mid Holocene has been supra-tidal terrestrial (fluvial/floodplain), and this may have been facilitated by a minor sea-level regression and rapid fluvial sedimentation. High resolution pollen and charcoal record from Central Kalimantan peatland provide a picture of forest succession, environmental change, and fire history from Early to Mid Holocene. Initial peatland colonization was represented by taxa which were already common in the area prior to the development of peatland forest. Subsequently, mixed swamp forest developed from Early Holocene to ca. 8000 cal yr BP. Camnosperma forest replaced the mixed swamp forest at some places after this time to ca. 7500 cal yr BP. This forest might have been a transitional forest prior to the development of Dacrydium forest from ca. 7500 to 5000 cal yr BP. Initial development of Dacrydium forest might have been triggered by a big peatland fire, which occurred in coincidence with the onset of dry soil condition after ca. 7500 cal yr BP. The presence of mangrove pollen in inland peat, about 150 km from present coast indicates that mangroves grew close to the site before ca. 7500 cal yr BP. High frequency of montane pollen and sand-rip-up clasts in peat, and Mid-Holocene peat-covered-sand suggest the strengthening of fluvial process after ca. 7500 cal yr BP. Numerous charcoal layers and microcharcoal particles in peat provide evidence that fire occurred frequently in the peatland from its initial development ca.10,000 cal. yr BP to the present. The fires were mostly local in extent, as indicated by spotted distribution of charcoal layers, and probably anthropogenic in origin because there is almost no natural fire source and water table in peatland is high through the year, while people has been present in Kalimantan since 35,000 yr BP. Additionally, peat stratigraphy, peatland structure and C-14 dates demonstrate that during the period from pre Holocene to ca. 10,000~9000 cal. yr BP, alluviation occurred extensively in Central Kalimantan. This alluviation and associated river migration promoted development of vast waterlogged environments which allowed peat accumulation. The peat is meso-ombrothropic in origin. The main period of peat accumulation from ca. 10,000 to 7500 cal. yr BP, occurred at relatively high rate of 0.07-0.1cm/yr. The accumulation rate of peat has slowed down to 0.008 cm/yr during the period from ca. 7500 to 5000 cal. yr BP, which may be related to drier climatic conditions. Since last ca. 5000 cal yr BP, peat accumulation has ceased or decomposition has prevailed. Penerbit HALIMA, 2014