Date of Graduation

5-2026

Document Type

Thesis

Degree Name

Master of Science in Geography (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Stahle, David

Committee Member

Brad, Peter

Second Committee Member

Holland, Edward

Keywords

conservation; Cross Timbers; forests; old-growth; outreach

Abstract

The Cross Timbers ecoregion represents a critical ecologic transition zone, spanning approximately 17 million acres across Oklahoma, Texas, Kansas, and Arkansas. Situated between eastern deciduous forests and the southern Great Plains, the Cross Timbers are dominated by drought-tolerant post oak (Quercus stellata) and blackjack oak (Quercus marilandica). Despite retaining some of the most extensive old-growth forests in the eastern United States, this ecoregion remains threatened by urban expansion, agricultural conversion, altered fire regimes, and eastern red cedar (Juniperus virginiana) encroachment. This project sought to identify, survey, and document large, previously un-surveyed or unreported tracts of old-growth Cross Timbers in Oklahoma, and to characterize the age, growth rates, and areal coverage of their oldest trees for landowner outreach and conservation. To aid in this, a machine learning-based predictive model was developed in Google Earth Engine using a supervised Random Forest Classifier trained on Sentinel-2 spectral and texture data. This resulted in an estimate of approximately 933,092 acres of old-growth forest remaining across the ecoregion, or 5.35% of the total Cross Timbers land cover. The model achieved an overall accuracy of 89.1%, a user's accuracy of 92.1% for old-growth, and a Cohen's Kappa of 0.75. Selected field surveys were also conducted at nine sites across Oklahoma using a Rapid Site Assessment framework, with dendrochronological sampling of seven sites and the non-destructive increment coring of 350 post oak during this project. The oldest post oak yet documented was found at the Charles Page Trust Property, with a minimum age of 445 years and an inner date of at least 1580. Average annual diameter growth for post oak across sites ranged from 1.29 to 1.51 mm, documenting the low growth rate for these deciduous hardwoods near the arid western limits of their natural distribution. Similar work in the Cross Timbers has already resulted in conservation successes, namely, the establishment of the Keystone Ancient Forest. Likewise, the findings and results described in this report demonstrate the efficacy of this survey framework, including changes to the Osage Nation's land management plans and increased landowner awareness of the unique Cross Timbers old-growth forests. These results also demonstrate the effectiveness of rapid, low-cost field assessments in advancing old-growth forest protection.

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