FIRE HISTORY, LANDSCAPE CHANGE, AND HUMAN RESPONSE TO HOLOCENE CLIMATE CHANGE IN BIG BELT MOUNTAINS, CENTRAL MONTANA

The Big Belt Mountains of central Montana provide an outstanding location for an integrated study of ecological change, landscape history, and early human activity in response to shifts in Holocene climate. This geographic, ecological and cultural transition zone between the Rocky Mountains and Great Plains is relatively under-studied, and climatic impacts on landscapes there remain poorly understood.

A long term archeological study, in partnership with Helena National Forest, is providing a comprehensive record of prehistoric human occupation. Multiple sites, situated along an ecological gradient, range in elevation from 7000 ft to the Missouri River at 4000 ft. Paleoclimate data (pollen, snails, charcoal) from several of the lower elevation sites suggest a shift to warmer drier climate, higher fire frequency, and increase in sedimentation for a brief period around 2000 yr BP. Human occupation and resource use also shift in response to these changes. The higher elevation sites extend back to 8000 years, and show evidence of erosion/depositional events between 3400-1500 cal yr BP. The evidence for warmer and drier climate around 2000 yr BP is present but difficult to constrain chronologically and correlate across archeological sites alone.

A continuous record of fire history, sedimentation, and paleoecology is being reconstructed from lake sediments retrieved from a small kettle lake located at 6400 ft on the east side of the range. A 4200 year record of fire history indicates a period of high fire intensity and frequency from 3700 to 3000 yr BP followed by a period of lower intensity fires centering on 2500 yr BP. An increase in wood charcoal abundance around 1800 yr BP and a peak in magnetic susceptibility around 2000 years ago indicate a change in sedimentation. Floodplain and terrace sediments also suggest changing deposition rates suggesting periods of drier climate and higher fire intensity. The 2017 field season will provide stronger dating control and integration of the archeological record with landscape changes recorded in lake sediments.

This interdisciplinary and comprehensive study provides a greater understanding of relationship between paleoenvironmental change and prehistoric population adaptations and the linkages between climate and landscape processes from the Holocene to present.