Date of Graduation

5-2023

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Stahle, David W.

Committee Member

Feng, Song

Second Committee Member

Bragg, Don C.

Keywords

Climate history; Dendrochronology; McCurtain County Wilderness Area; Shortleaf Pine

Abstract

Increment cores were extracted from 483 trees distributed over 21 semi-randomly sampled 0.1-hectare plots on three distinct landscape positions in the McCurtain County Wilderness Area (MCWA), a 57 square kilometer tract of uncut shortleaf pine in southeastern Oklahoma. Forty additional cores were taken off plot from older-appearing trees. All sampled trees were shortleaf pine (Pinus echinata) with a diameter at breast height (DBH) of at least 10 cm. Hardwoods were not included in the size and age analyses. The study site chosen for the sampling was made up of four parallel east-west trending ridges near North Linson Creek, making up about 1.3 square kilometers in area. The cores and diameter measurements were used to examine the age, size, basal area, density, and growth rate of the sampled pine stands. All core samples were dated dendrochronologically using the Douglass method of cross dating (Douglass, 1941) and measured for the development of earlywood (EW), latewood (LW), and total ring width (RW) chronologies. The average diameter for all randomly sampled trees at Linson Creek was 31.3 cm at breast height, and the average age was 100.3 years (i.e., the minimum age, based on core sampling at breast height). The size-age correlation was found to be stronger for the pines with a diameter of over 40 cm. A major pulse of shortleaf pine recruitment to breast height was detected from 1920-1940, when a sizable group of sampled trees reached ~1.4 m. Cumulative radial growth curves showed a wide variety of growth rates. When the effect of topographic position was tested, south-facing plots were found to have both the oldest and slowest-growing trees on average, and the youngest and smallest were found on the north-facing plots. Ridgetop plots had both the largest and fastest growing pines. The final chronology for Linson Creek dates from 1743 to 2020, and includes some individual trees cored outside of the randomly sampled plots due to their old appearance. These off-plot samples were not used for the dendroecological analyses, which were based only on the randomly sampled trees. Data from Stahle et al. (1985) were subsequently added to the Linson Creek samples to construct final, fully replicated chronologies of EW, LW, and RW, which extend from 1688 to 2020. The measured EW, LW, and RW chronologies were correlated with gridded instrumental Palmer Drought Severity Indices (PDSI) for the United States from 1895-2005. Results showed a significant positive correlation between latewood width and August PDSI in the same year as ring formation, not just in McCurtain County but also the surrounding states. Earlywood growth, by contrast, was only weakly correlated with June-July PDSI in the summer one year prior to EW formation.

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