Bighorn Mountains Dendrochronology


Trapper Canyon Douglas fir climate response

These results are preliminary and unpublished. Please do not cite or distribute.

The Palmer Hydrological Drought Index (PHDI) for Wyoming climate division 4 is significantly correlated with the standard chronology of Douglas fir ring width indices from Trapper Creek Canyon. The strongest correlations are with June PDSI and June PHDI, which is graphed below, but every month of these indices from May to August is significantly correlated wth the annual ring width indices. Other divisional indicies and single-station records are also significantly correlated with the Trapper Canyon chronology.

Although a lag of one or two years between PHDI and the trees' ring width response is evident in the top graph (below) severe drought years are associated with the simultaneous production of very narrow (or absent) rings. This synchronous response is apparent below in 1919, 1934, 1966, and 1994. Longer term trends in 20th century PHDI are also well mirrored by the tree ring chronology suggesting that the entire 500 year chronology could have interpretable information about multi-decadal periods of past drought stress.

The scatterplot below includes a correlation coefficient and a regression coefficient (in red) for a linear regression which is graphed through the data.






Met data