Pollen analysis of a 7.65 m sediment core from Eaglenest Lake (57°46′N, 112°06′W) provides evidence of the postglacial development of vegetation in the mixedwood section of the Boreal Forest. From the time of deglaciation (approximately 12 000 – 11 500 years BP) to 11 000 BP the area was colonized by mainly nonarboreal flora dominated by Artemisia and Gramineae. Populus, the only tree taxon present, grew in sheltered areas, while Salix and Cyperaceae were common on poorly drained sites. Open parkland prevailed under a dry, windy climate. Summer temperatures were rising rapidly from glacial minima in response to increased solar insolation. By 11 000 BP Picea (initially P. glauca) and Betula (mainly tree Betula) migrated to the area. Forest prevailed, but the canopy was likely more open than at present. By 9000 BP peak warm and dry conditions had passed, although conditions warmer and drier than at present persisted. Alnus migrated to the area 8450 BP. Pinus reached the Birch Mountains about 7500 BP. No major changes in vegetation have occurred since that time, suggesting that modern climatic conditions were established by 7500 BP.