Episodic and Systematic Tree Ring-Width Variation (AD 1763–2013) in the Takhini Valley, Southwest Yukon, Canada

Abstract

A tree-ring analysis of 764 western white spruce (Picea albertiana) in the Takhini Valley of southwest Yukon was conducted to assess short- and long-term variation in growth and local climate. The resulting chronology spanned the period from AD 1763 to 2013. A polynomial regression (R = 0.720, p < 0.001) indicated that the pre-1840 segment of the chronology had below-normal tree ring-width index (RWI) values (average 0.64, with modest variation), but the subsequent segment had greater variation and a steady increase in RWI values (average 0.89) until ~1920. After 1930, RWI values began to increase again (average 1.06) with 51% more variation than had previously occurred. Peak RWI values after 1930 were double those of the early 1800s. RWI values were uncorrelated with air temperature variables (except September minima), but weakly and positively correlated (r < 0.35) with precipitation variables. RWI values were moderately correlated with annual heat-moisture index values (r = −0.415, p < 0.001), although more strongly with RWI values less than 1.1 (R = −0.631, p < 0.001). Therefore, the RWI chronology was interpreted from an ecological moisture-balance perspective, with possible long-term temperature changes estimated from archival sources. The latter suggested a 2.1˚ – 3.1˚C rise since the early 1800s. Extreme RWI values and portions of the chronology were associated with known environmental events.

Patterns of vegetation change in Yukon: recent findings and future research in dynamic subarctic ecosystems

“…Previous shifts in Yukon's climate have resulted in significant changes to vegetation communities. For example, throughout the Holocene, there was conversion from balsam poplar forests to tundra Spear 1991, 1995), and in the 19th century spruce stands in southern Yukon were more abundant than they are now (Strong 2017(Strong , 2020.…”