Bighorn Mountains Dendrochronology

Inferno Canyon Limber Pine chronology

 

 Chronology description

These results are preliminary and unpublished. Please do not cite or distribute.

This chronology includes 14 ring width series from 9 living and 2 dead limber pine trees sampled near the rimrock around Inferno Canyon in the Pryor Mountains near Bridger, MT. Sample depth in 1600 is 5 series from 4 trees. Two series from 1 tree extend back to 1500. The shortest series is 147 years. Additional sampling of live trees could strengthen the chronology and extend it 100-200 years, and the collection of remnant material also has great potential.

Each ring width series was detrended using a negative exponential curve or straight line of 0 or negative slope. The length of these series and the conservative detrending allow interpretation of trends as long as 100-200 years. The orange line below is a 25 year cubic smoothing spline which highlights these trends.

Five of the 14 series had a total of 11 missing rings for an average of 1.3 missing rings per series. The most common years of missing rings are 1848 and 1863. The location of these missing rings was determined by visually cross dating each core using narrow marker rings which are consistently present in most decades in each core. There is strong intercorrelation of ring widths among series (r=.699), and high mean sensitivity (.383) making crossdating straightforward.

Interpretation

The good correlation of the 20th century portion of this chronology with Wyoming division 4 PHDI suggests that this preliminary chronology could be used as a proxy for regional drought stress or precipitation. The chronology suggests that droughts during the 1600s and 1700s were more severe and more prolonged than droughts since 1800. The well-documanted droughts of the 1930s and 1950s were not experienced by these trees as strongly as were earlier droughts. Oscillations of the smoothed chronology at a frequency between 40 and 100 years are similar to the low-frequency variation in the Trapper Canyon Douglas fir chronology. (see Synthesis).

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