Abstract
The manual and digital measurements of fossil tree rings from the Jurassic Morrison Formation are compared across localities to determine forest dynamics and the ancient climate in the American Southwest, primarily near Vernal, Utah. Mean sensitivity is utilized to estimate variability between rings. Locality based dendrochronology addresses major concerns in conservation, namely at a regional level. There is broad, qualitative knowledge about global climates in the Jurassic, but ascertaining specific, regional climate reconstruction has been difficult (Hallam, 1982). This study aims to 1) test the use of modern-calibrated dendrological programs on ecosystems of the geologic past, 2) use analyzed deep time forests as an analog to modern climatic projections which fail to meet the goals of the Paris Climate Agreement (2015), 3) place analyzed palaeobotanical specimens in geologic context and utilize interdisciplinary approaches in the reconstruction of paleoclimates, and 4) utilize these comparative data on Jurassic period conifers to make predictions on extant ecologically threatened conifers in today's rapidly changing climate. Mean sensitivity analysis is used to constrain regional climates in projective analogs, as communities experience climate change most prominently at a regional level (Environmental Protection Agency, 2025). Mean sensitivity analysis of 22 fossilized wood samples yielded with an average ring width of 2.72 mm, a maximum width of 12.5 mm, and a minimum width of 0.2 mm. Samples show some variation in ring widths, which may be indicative of singular storm events or seasonality. The Rainbow Draw and Miner's Draw localities both have anomalously wide rings compared to the average of the locality. The Miner's Draw locality also has a significantly lower mean than the other localities, with the mean of means being 3.05 mm. The average mean sensitivity value across all samples is 0.5243, indicative of a variable climate. Climate variability changes if each site is examined as its own locality, with mean sensitivities ranging from 0.2402 at the lowest, or most equable, to .7044 in the Manwell log from the Jensen Bench locality. The most successful correlations between fossil trees in a locality yielded correlation coefficients of .75 and .57 between the Wagon Bench and Miner’s Draw localities respectively. These coefficients are indicative of a high level of correlation between ring chronologies and may indicate concurrent growth between Jurassic fossil trees.