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An emerging trend in tree-ring research is use of multiple species for reconstructing paleoclimates, but the possible simultaneous use of boreal-cordilleran species is untested. In this study, ring-width chronologies of sympatric Pinus contorta (lodgepole pine, n = 116 series) and Picea albertiana (western white spruce, n = 348 series) were constructed to assess their temporal (dis)similarities and correlative relationships with meteorological variables. Chronology construction was based on multiple Regional Curve Standardization. Most (97.5%) Pinus chronology values occurred within ±1 SD of their Picea counterparts, but Picea values tended to be slightly less (sign-test, p < 0.001, n = 201). Pinus ring widths were more frequently (16 versus 9) and more strongly correlated (U-test, p < 0.009) with 1942-2013 meteorological variables than Picea. Both species were correlated with moisture variables, but Picea was not correlated with those of temperature. Pinus and Picea ring-width variation was best explained by summer (r = -0.434) and annual (r = -0.426) heat-moisture index values (p < 0.001, n = 72) among tested variables, respectively. Although seldom used, P. contorta appears as suitable as conventionally-used P. albertiana based on chronology similarity, but a greater diversity of significant correlation outcomes suggest Pinus is potentially more useful for boreal-cordilleran paleoclimate reconstruction. [ABSTRACT FROM AUTHOR]

Western North American lodgepole pine (Pinus contorta var. latifolia Engelmann ex S. Watson) releve's (n = 6,918) were classified to identify regional difference in understory vegetation types. Seventy-nine types with > 5 releve's were recognized, but only 34 included > 40 releve's. Among the latter, shrubs dominated 15 types, excluding consideration of feathermosses. Buffaloberry (Shepherdia canadensis (L.) Nutt.), twinflower (Linnaea borealis L.), and bearberry (Arctostaphylos uva-ursi (L.) Spreng.) understory types spanned most of the latitudinal range. Eleven types occurred only north and four only south of ~50° N latitude. Latitude explained ~82% (P < 0.001, n = 5,759) of the elevation variance among releve's, with a northward decline decreasing from 81 to 21 m/degree of latitude. A discontinuity in elevations at ~50° N is thought to represent a northward shift from a cordilleran-prairie to a cordilleran- boreal ecoclimatic regime. A comparison of releve' and regression-predicted elevations identified 18 understory types that differed (P ⩽ 0.02) from the regional trend. May-August solar insolation, which was used as a proxy for latitudinal differences in slope gradient and orientation, indicated that ~77% of P. contorta releve's were associated with more intensive solar insolation sites. When cross-referenced with elevation, 13 types differed from the norm in terms of both elevation and insolation. The results provide a framework for more detailed forest classification. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]