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

Wayne L Strong

doi:10.14430/arctic4685

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.

Highlights

The Intergovernmental Panel on Climate Change (IPCC, 2013:22) predicted a 1 ̊ – 1.5 ̊C to 4 ̊ – 5 ̊C increase in average annual temperature above the 1986 – 2005 level in the Canadian boreal forest by AD 2100
The lack of correlation between Takhini Valley ring-width index (RWI) values and temperatures was contrary to the results reported by Davi et al (2003) and Youngblut and Luckman (2008), who analyzed sites near the tree line in the southern Yukon
Davi et al (2003) and D’Arrigo et al (2004) noted that high-elevation spruce became less sensitive to warming summer temperatures after 1970. This fact suggests that moisture availability became a more critical constraint, and it implies that tree-ring growth in valley bottoms may have become more moisture limited, possibly at a somewhat earlier date

Summary

Introduction

The Intergovernmental Panel on Climate Change (IPCC, 2013:22) predicted a 1 ̊ – 1.5 ̊C to 4 ̊ – 5 ̊C increase in average annual temperature above the 1986 – 2005 level in the Canadian boreal forest by AD 2100. 390 W.L STRONG are predicted to be warmer by the end of the 21st century, climate modeling indicates total annual precipitation will increase less than 10% above 1986 – 2005 levels in the Yukon region (IPCC, 2013:22). A rise in temperature without a corresponding increase in effective moisture could have a long-term effect on the physiognomy and botanical composition of the indigenous vegetation, as well as on conifer tree growth (m3 ha-1 yr-1) (Wang et al, 2006; Miyamoto et al, 2010; Griesbauer and Green, 2012). Changes in vegetation could in turn affect the composition and abundance of wildlife in the territory

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Discussion

Conclusion