Microfossil evidence of land-use intensification in north Thailand

Palaeo-environmental data from accumulated lake sediments at Phayao, northwest Thailand, provide a record of vegetation and environmental change from approximately 20,000 years Before Present. This is an important region archaeologically, with claims in the 1970s for an 'early' transition to domestication having arisen from a number of cave sites. Multiple indices are used to determine if people had an observable impact on the natural environment, and to determine the timing and magnitude of impacts associated with the development of agricultural land use in the region. An initial increase in sedimentation rate is apparent from ca. mid-2nd C AD. Changes in phytoplankton concentrations are apparent from the late 3rd C AD, and evidence for initial forest disturbance is apparent from the 5th or 6th C AD, with impacts becoming more severe over time to reach a pre-modern maximum in the 11th to the 13th C AD. Changes in agricultural practices are apparent during the 14th C AD, with an increased emphasis on rice agriculture and incipient management of the regenerating forests. Based on these data we suggest that agricultural intensification in the early part of the 1st millennium AD destabilised catchment slopes, through clearance of dryland vegetation and swidden agriculture. There is no direct evidence for the impacts of earlier peoples on the vegetation of the area, which we take to indicate that agricultural intensification was later here than in the lowlands to the east and south.