Tree-ring widths of Picea engelmannii at Andrews Meadow, Rocky Mountain National Park

Andrews Meadow in the Loch Vale watershed, Rocky Mountain National Park. Sample Collection: Englemann spruce (Picea engelmannii) living on slopes surrounding and at the edge of Andrews meadow (Latitude 40˚ 17’ 24” N, Longitude 105˚ 40’ 01” W NAD83). At the time of collection, the climate-sensitive upland P. engelmannii trees were growing on well-drained slopes above the meadow. Seventeen trees, two cores per tree when possible, were collected using a 5mm-diameter increment borer. During sample collection, diameter at breast height (DBH) was also measured. These cores were processed following standard dendrochronological methods. The annual (TW) and earlywood (EW) ring-widths of each core were measured to 0.001mm precision using a Velmex stage and Tellervo measuring software. Visual crossdating was verified statistically using the ring-width measurements in the program COFECHA v.6.06P. Cores with breaks or rot precluding robust statistical crossdating were removed from further analysis. Final COFECHA statistics for TW indicate series intercorrelations of 0.544 and average mean sensitivity of 0.199. Final COFECHA statistics for EW indicate series intercorrelations of 0.546 and average mean sensitivity of 0.214. The tree-growth trend was removed using a negative exponential curve and the detrended ring-widths were then averaged and standardized for unitless site level standard chronologies (std) of TW and EW. Pre-whitened TW and EW chronologies (res) are the residuals from an autoregressive model (AR1) which removes year-to-year serial correlation commonly present in tree-ring series. The Earlywood record is begins at 1513 because it has been truncated to an acceptable Expressed Population Signal (EPS>0.85). The EPS is an arbitrary statistical threshold above which the chronology is deemed statistically acceptable for climate reconstruction.