Date of Award

8-2026

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

School

Biological, Environmental, and Earth Sciences

Committee Chair

Clay Tucker, PhD

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Nathan Beane, PhD

Committee Member 3

Maegen Rochner, PhD

Abstract

Quercus spp. suppression may be concomitants of Juniperus virginiana L. encroachment in woodland and savanna ecosystems, raising questions about conservation and the potential loss of paleo-proxy data for these regions. In the United States (U.S.), this encroachment is especially impactful along the transitional forest-prairie ecotone. The Cross Timbers region woodlands were historically dominated by post oak (Q. stellata Wangenh.) and blackjack oak (Q. marilandica Münchh. var. ashei Sudw.), but today this region features greater proportions of eastern redcedar (J. virginiana L.). Isolated Quercus relics of the Cross Timbers ecosystem are particularly vulnerable to these changes, and their growth patterns provide important insight into changes of the broader ecoregion. Elk City Lake reservoir in southeastern Kansas provides water to the area and is flanked by an upland forest that is characteristic of the Cross Timbers ecosystem. At this site, Quercus spp. grow alongside J. virginiana. Few previous studies have assessed the climate response, disturbance regimes, and response to J. virginiana encroachment of Q. stellata in the Cross Timbers ecoregion. I generated both J. virginiana (1928-2023) and Q. stellata (1883-2023) tree-ring chronologies and compared mean growth responses to monthly and seasonal climate variables. Additionally, I investigated regime-shift related changes in moisture sensitivity by using a moving correlation analysis with recorded Palmer Drought Severity Index (PDSI) values. Moving correlation analysis indicated Q. stellata exhibited a relationship with all climate variables tested, though these relationships are not stable through time. This trend was punctuated by a period of increased sensitivity in the 1960s and 1970s. J. virginiana showed a correlation to climate that increased over time, later becoming statistically significant. Regime shift analysis of mean Q. stellata growth determined a statistically significant (p < 0.05) decrease within a 20-year period centered in 1940. Disturbances concurrent with this period include anthropogenic influences such as the construction of Elk City Lake reservoir and reduced wildfire frequency as well as J. virginiana encroachment. This increased understanding of J. virginiana impacts on Q. stellata growth suppression and climate response will inform conservation of these ecosystems as they continue to face pressure from increased J. virginiana encroachment and climate variability.

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