Separating climatic and possible human impacts in the early Holocene: Biotic response around the time of the 8200 cal. yr BP event

The early Holocene is characterised by rapid climate change events, which in the North Atlantic region are often associated with changes in thermohaline circulation. Superimposed on this in northwest Europe is localised evidence for human impact on the landscape, although separating climatic and anthropogenic mechanisms for environmental change is often difficult. Biotic and sedimentological evidence from a lacustrine sequence from the Inner Hebrides, Scotland, shows a considerable reduction in inferred local woodland centred upon 8250 cal. yr BP. These data correlate precisely with a distinctive rise in the charcoal:pollen ratio and hence suggest a possible Mesolithic human impact upon the vegetation around this time. A quantitative temperature reconstruction from chironomid analyses from the same sequence, supported by sedimentological data, indicates that the fall in arboreal pollen taxa occurred as climate warmed significantly during the early Holocene. This warming was followed by a significant cold event, with mean July temperatures reduced by 2 degrees C, that lasted for at least 320 years ca. 7790-7470 cal. yr BP. Woodland recovered during this phase suggesting that the vegetation during the 8250 cal.yrBP interval was likely to have been responding to human activity, and not climate, and hence it is possible at specific sites to separate the influence of these key drivers of environmental change.