Holocene Environmental Change in Mainland Southeast Asia: Pollen and Charcoal Records From Cambodia.

Abstract

Major Holocene environmental changes in continental Southeast Asia are reconstructed using proxy data derived from analysis of 14C-dated changes in pollen, microscopic charcoal, and organic/inorganic carbon in sediment cores taken from permanent, closed-basin, volcanic lakes in Ratanakiri Province, northeastern Cambodia. Analysis focuses on the history of monsoon climate and land use, inferred from changes in vegetation, fire regime, and lake conditions. These data provide the first well dated palynological record, covering most of the Holocene and continuous up to the present, from an upland site in mainland Southeast Asia. The record from a 15-meter core retrieved from Yeak Kara Lake, representing the last 9300 years, shows that the Late Glacial period ended about 8500 BP, more than 1000 years later than sites in southwest China. Maximum summer monsoon intensity occurred ca. 8000--5400 BP, similar to most other sites in the Asian monsoon region. A subsequent increase in burning caused expansion of secondary forests at the expense of dense semi-evergreen forests. After ca. 3500 BP fire frequency may have increased further, leading to expansion of dry deciduous forests. From ca. 2500 BP up to the present, dense forest has recovered in a mosaic with annually-burned dry forest, due either to a Late Holocene strengthening of the monsoon or to more pervasive control of the fire regime by indigenous populations. The pattern of burning for the last 2500 years, corroborated by charcoal records from two other nearby lakes, shows lowest burning intensity perhaps coinciding with the development and demise of major civilizations (Funan, Chenla, Angkor) in the region.