VEGETATION HISTORY OF THE LATE HOLOCENE IN EAST GLACIER NATIONAL PARK, MONTANA: A PALEOENVIRONMENTAL STUDY

The Medieval Warm Period (MWP) was an interval of prolonged warmth in northern Europe from 1050 – 750 cal yr BP. Data from elsewhere in the Northern Hemisphere indicate that there may have been several pulses of warmth occurring at significantly different times in different locations. The Little Ice Age (LIA) was a period of modest cooling in northern Europe from 550 – 150 cal yr BP. Outside of northern Europe, evidence for periods of cooling occurs from 750 – 50 cal yr BP. The apparent temporal and spatial variability of both the MWP and the LIA suggests that more research is necessary to determine the timing, extent, and effects of these climate anomalies across the Northern Hemisphere.

This study examines the vegetation history of Many Glacier Valley using pollen samples extracted from a sediment core taken from Swiftcurrent Lake (SWF) in East Glacier National Park (GNP), MT, focusing on the past 1200 years. The data show a slight retraction of the forest cover and an increase in steppe vegetation during the MWP. Additionally, a high abundance of xeric pollen taxa indicates that the MWP in GNP was likely drier and warmer than the preceding and subsequent time periods. The MWP in East Glacier National Park was likely a period of gradual warming with a peak of warmth and aridity ca. 1160 cal yr BP, indicated by a maximum in Pinus pollen abundance and the minimum abundances of Abies lasiocarpa, Picea engelmannii, and Alnus viridis. Preliminary charcoal data show an above-average fire frequency during the MWP, which support this interpretation. During the LIA, the forest expanded into the modern flora of GNP. Increased mesic taxa indicate more available moisture, and increases in the abundance of A. lasiocarpa and P. engelmannii suggest a cooler climate until ca. 185 cal yr BP when xeric and non-arboreal pollen increased. Charcoal accumulation rates decreased dramatically ca. 600 cal yr BP, consistent with the onset of the LIA, and then increased ca. 150 cal yr BP, the end of the LIA. This study, one of the only to study the MWP and LIA east of the Continental Divide, indicates that these climatic anomalies affected the Northern Rocky Mountains at slightly different times than in other parts of the Northern Hemisphere. The MWP seems to have occurred slightly earlier, and the LIA likely ended earlier than the end of the LIA in Europe.