Holocene migration of lodgepole pine ( Pinus contorta var. latifolia) in southern Yukon, Canada

• Published in: The Holocene
• Main Authors: Strong, Wayne L, Hills, Leonard V
• Format: Article in Journal/Newspaper
• Language: English
• Published: SAGE Publications 2013
• Subjects: Carcross; Teslin; Teslin River; Yukon
• Online Access: http://dx.doi.org/10.1177/0959683613484614; http://journals.sagepub.com/doi/pdf/10.1177/0959683613484614; http://journals.sagepub.com/doi/full-xml/10.1177/0959683613484614

A palynological reconstruction ( n = 25 profiles) suggests that the northern extent of lodgepole pine ( Pinus contorta var. latifolia Engelmann ex S. Watson) occurred between 59° and 60°N latitude in northwest North America from 10,000 to 7000 calendar years before present (cal. yr BP) prior to entering Yukon. Although specific migration pathways could not be resolved with the available palynological data, mountains along the southern edge of Yukon appear to have diverted lodgepole pine migration through the Carcross and Frances Lake areas in southwest and southeast Yukon, respectively. Migration in the southwest (70 m/yr) was likely confined to lower elevations of the Yukon and Teslin river valleys, with lodgepole pine reaching 61°N ~2000 cal. yr BP. Along the eastern route, migration was channeled through a 15–20 km wide pass in a 200 km mountainous front. After breaching the Liard drainage divide north of Frances Lake ~4000 cal. yr BP, migration progressed northwest (160–220 m/yr) along the Tintina Trench. Lodgepole pine was estimated to have reached its near present-day northern limit (~63°N) ~1790 cal. yr BP, which is ~1290 years earlier than previously thought. This difference in arrival dates is due the use of a >5% rather than a >15% pine pollen content threshold, which appears to correspond with >1% pine tree cover in the landscape. Climatic cooling after 1000 cal. yr BP that caused a population decline at higher elevations is hypothesized to explain the present-day sparse and disjunct distribution of pine across Yukon north of 61°N.