Post-glacial vegetation history of the Mission Mountains, Montana

• Published in: Journal of paleolimnology 1995-11, Vol.14 (3), p.269-279
• Main Authors: Gerloff, Lisa M., Hills, L. V., Osborn, G. D.
• Format: Article
• Language: English
• Subjects: Freshwater
• ISSN: 0921-2728; 1573-0417
• DOI: 10.1007/BF00682428

A pollen record from Rock Lake in the Mission Mountains, northwestern Montana reveals a four-zone sequence reflecting Holocene vegetation change. Chronologic control is provided by two well-known tephras, Glacier Peak (11 200 yr B.P.) and Mazama (6800 yr B.P.). The presence of Glacier Peak tephra above the basal inorganic sediments indicates deglaciation prior to 11 200 yr B.P. Colonizing vegetation (Zone I) after the fall of Glacier Peak tephra was dominated by Artemisia (sage) and Alnus (alder). The presence of Abies needles, Picea needles, and one Taxus needle in the core demonstrates that these taxa were at Rock Lake at the time Zone II sediments were deposited. The increase in Pinus, Picea, and Abies pollen in Zone II (10 850-4750 yr B.P.) suggests warmer and drier conditions prevailed, and may record the Hypsithermal. The pervasiveness of Picea and Abies pollen in Pollen Zone III (4750-3350 yr B.P.) suggests the emergence of the modern subalpine forest. Pollen Zone IV (3350 yr B.P.-present) is characterized by relatively little change in the pollen assemblages. One noted change, however, is the increase of Cyperaceae (sedge), which may indicate an expansion of shore-line around the lake, possibly reflecting increased precipitation.