Date of Graduation

12-2023

Document Type

Thesis

Degree Name

Master of Science in Geography (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

David W. Stahle

Committee Member

Paradise, Thomas R.

Second Committee Member

Ogle, Jennifer D.

Keywords

Dendrochronology, Dendroclimatology, Forest ecology, Old-growth forest, Ozarks, Shortleaf pine

Abstract

Shortleaf pine (Pinus echinata) approaches the westernmost limits of its range in the Arkansas Ozarks. Despite heavy logging of shortleaf pine throughout its range during the 19th and 20th centuries, the species was not easily accessible for harvest and transportation in the most rugged areas of the Boston Mountains and, as a result, there are a few extant stands of old-growth shortleaf pine in the region. The shortleaf pine stands in the interior Boston Mountains are unusual in that they exist primarily above bluff lines at topographic breaks in the hardwood canopy and are not disturbed by fire as frequently as stands with lower topographic roughness. Because of the continual decline of shortleaf pine throughout its range, multiple organizations, including the U.S. Forest Service, are interested in restoring the species (Hedrick et al. 2017; Oswalt 2013). This study analyzes the age-structure and species composition of select old-growth shortleaf pine stands to characterize remnant old-growth pine-hardwood forests in the Boston Mountain region of the Arkansas Ozarks, and to inform plans to restore the declining species. To determine the age structure and composition of select shortleaf pine stands, increment cores were extracted from approximately 450 trees distributed over a series of five sites in the Upper Buffalo River and Mulberry River watersheds. All trees that were core sampled are shortleaf pine at least 10 cm in diameter at breast height (DBH). The study sites chosen for sampling were selected for a pine-dominant ecotype and little to no evidence of human disturbance. The cores extracted were used to examine the size, age, basal area, density, and growth rate of the sampled pine stands. All core samples were dendrochronologically dated, and a subsection of the samples was measured for the development of total ring-width (RW) chronologies using the Douglass method of crossdating (Douglass 1941). At the Upper Buffalo River sites, shortleaf pine had an average DBH of 25.7 cm, and an average minimum age of 91.4 years. The relationship between size and age at these sites was relatively strong, with an average correlation of 0.61. When divided at a 40 cm threshold, the correlation deteriorated significantly in larger trees (r = 0.44), while the correlation coefficient became stronger in trees with a DBH < 40 cm (r = 0.66). There is evidence of multiple recruitment pulses at each site. Most of the trees sampled were recruited to breast height between 1950 and 1970, although there were smaller recruitment pulses from 1860-1870, and from 1910-1940. Cumulative radial growth curves were similar at each of the four sites in the Upper Buffalo River watershed. The final chronology for the Upper Buffalo dates from 1782-2022. The Mulberry River site was similar, but contained older, larger, and faster growing shortleaf pine trees. The measured RW chronologies for both the Upper Buffalo and the Mulberry were correlated with May-August total precipitation and May-August average maximum temperatures on a 0.5°latitude/longitude grid over the United States from 1951-2020. The spatial response to climate differs across the Boston Mountain divide, with the Buffalo River shortleaf pine RW chronology most highly correlated with precipitation (PPT) and temperature data in northwest Arkansas and northeast Oklahoma, while the RW chronology of the Mulberry River shortleaf pine was more highly correlated with PPT in southwest Arkansas, northwest Louisiana, and northeast Texas (the “Ark-La-Tex” region). No cut stumps or other signs of human disturbance were present at any of the study sites, indicating that these sites represent one type of uncut old-growth shortleaf pine community. These results may help to inform forest-management practices, as well as to build a foundation for further ecological and climatological research.

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