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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.

The study of biodiversity has long been a core component of community ecology research and may be broken into three major themes: (1) describing patterns of diversity, (2) determining drivers of biodiversity, and (3) understanding consequences of diversity. The body of work presented in this dissertation addresses questions pertaining to these themes using long-term data collected in old-growth (primary) forests of both North America and Asia. In Big Everidge Hollow (BEH), a 52-hectare stand of old-growth forest in central Appalachia, I examined how relative abundances and spatial distributions of dominant tree species have changed over a 30-year period and tested for significant shifts in overall community composition. I also employed phylogenetic and functional diversity measures to better understand how environmental factors, particularly topography and soil characteristics, play a role in the assembly of tree communities. Data from the Fushan Forest Dynamics Plot (FDP), a subtropical broadleaved forest in Taiwan, were used to test whether taxonomic and functional diversity play a role in maintaining temporal stability of carbon storage (aboveground biomass and coarse woody productivity). Overall, I found that tree communities in BEH have been undergoing a shift in species dominance from oak (Quercus spp.) to maple (Acer spp.) over the past thirty years that is consistent with trends described in numerous other forests in eastern North America. Local tree communities in BEH are spatially structured across gradients of both topography and soil characteristics such that assemblages of low functional and phylogenetic diversity occur in areas of greater environmental stress (low soil moisture and nutrients, especially at high elevation and on south-facing slopes). The Fushan FDP data revealed weak yet significant biodiversity-stability relationships, indicating that as biodiversity increases, levels of ecosystem function (carbon storage, in this case) tend to be more consistent over time. As disturbance due to human activities continues to exert greater influence on natural ecosystems across the globe, the need to document changes in biodiversity becomes increasingly important. Employment of phylogenetic and functional diversity metrics can provide greater insight on the ecological consequences of shifting species dominance, especially in areas considered biodiversity “hotspots” that serve as reference ecosystems for restoration of degraded habitats and as baseline models for predicting future change. The work presented here aims to provide the necessary “control treatment” for understanding baseline patterns and drivers of diversity in comparison to anthropogenically-driven changes in forests across the globe.

Diversity and compositional dynamics in deciduous forests of eastern NorthAmerica are subject to a suite of potentially interacting ecosystem drivers, including, but not limited to, anthropogenic and natural disturbances, fire, exotic species invasions, climate shifts, and environmental gradients. The structurally complex Eastern Deciduous Forest is one of the most diverse temperate ecosystems, and despite decades of ecological research, many fundamental questions regarding spatial and temporal dynamics are either hotly debated or remain unanswered. The body of work presented in this thesis is part of an ongoing long-term botanical analysis of Big Everidge Hollow, a watershed containing old-growth forest within the Lilley Cornett Woods Appalachian Research Station on the Cumberland Plateau of eastern Kentucky. The relatively pristine condition of this site has provided a unique opportunity to study forest dynamics in an area of minimal anthropogenic disturbance. The first chapter of this thesis describes changes in the floristic community that have occurred since the last floristic survey of the site in 2001. Twenty-three new species records are reported, some of which are invasive species that pose a threat to the biological integrity of the site. The second chapter examined baseline dynamics of woody understory over a decade, described the relationships between diversity and surrogate measures of productivity (density and cover), and investigated the reaction of shrub- and ground-layer vegetation to a recent fire in one portion of the study site. Decadal oak-maple dynamics in the woody understory of this old-growth stand did not fully support the hypothesized oak-to-maple dominance shift thought to be occurring in forests across eastern North America; changes in shrub- and ground-layer populations of maple (Acer spp.) were erratic while oak (Quercus spp.) populations appeared stable. Unimodal relationships between diversity and productivity surrogates were found in both woody understory layers and are likely driven by the range of environmental conditions found within the study site. Fire induced short-term changes in the shrub- and ground- layers and may have facilitated colonization of invasive species. The third chapter aimed to understand how spatial patterns of both alpha (¿¿¿¿) and beta (¿¿¿¿) diversity in the herbaceous layer relate to topography and how these relationships vary over time. Shannon diversity varied linearly with aspect and slope, but unimodally with elevation, indicating steep, mid-elevation, and south-facing plots tended to be most diverse. These relationships were persistent, but weakened slightly, through the growing season. Significant spatial species turnover occurred across topographic gradients; compositional dissimilarity tended to be greater between plots with greater differences in aspect, slope, and elevation. Full-season temporal species turnover (i.e. compositional change over time) was weakly related to aspect (linear fit) and elevation (quadratic fit; r2 = 0.09, P < 0.05), suggesting greater species turnover occurred on north-facing and mid-elevation plots. The results presented here fit into a larger body of work conducted at this study site, which has the potential to serve as a model system to provide the necessary baseline knowledge for advancing ecological theory and developing conservation strategies.

Documenting change in the composition and structure of forest communities is important for understanding the distribution and abundances of natural resources, carbon pools, and species. Here, results are presented from the second sampling effort at Dysart Woods, an old-growth, mixed-mesophytic remnant tract in southeastern Ohio. In 2011, trees, saplings, shrubs, herbs, and soils were sampled in permanent plots established in 1996, allowing a direct fifteen–year comparison. Mortality and recruitment rates revealed that while most species at Dysart Woods are decreasing in abundance, sugar maple and American beech are rapidly increasing in importance, as is the invasive Alliaria petiolata. This shift in composition may be due to beech and sugar maple showing little negative responses to neighbors, and/or reflect increasing pressures that old-growth forests face from invasives. Such findings have considerable implications for the future of Dysart Woods, and developing appropriate management techniques may be required to preserve its integrity.

Subsurface coal mining is occurring near and underneath Ohio University’s Dysart Woods Land Lab, a 23 hectare old-growth forest. Such mining is associated with changes in groundwater hydrology throughout the region. However, the impacts of these hydrologic changes on forest ecosystems have not been studied. Public controversy over the mining has raised questions for which no answers exist in the peer-reviewed literature. This thesis addresses the question: How much moisture can the soils at Dysart Woods contain- and does groundwater contribute to the site water budget? As a pre-mining observation, volumetric water content of soil was measured in a spatially extensive and temporally intensive manner utilizing a combination of dataloggers, sensors, and hand-held meters in 2005 and 2006. The average soil depth was found to be 1.2 m and the plant-available water holding capacity of the soil was found to be 150mm. Analysis of the stable isotope content of groundwater, precipitation, and xylem water indicated that trees, even in upslope positions, were likely using groundwater during the growing season drought of 2005.

In order to determine baseline levels of carbon storage in an ecosystem it is necessary to survey minimally disturbed areas. Few studies have examined ecosystem carbon storage for old-growth eastern deciduous forests. Soil sampling plots were stratified according to slope ( N = 3), aspect ( N = 2) and stand age ( N = 2) to investigate their effect on soil C variability in old (> 350 year-old) and adjacent second-growth (~ 60 year-old) oak-beech-maple stands in eastern Ohio. Aboveground biomass data in the old and adjacent second-growth stands were combined with the soil carbon and forest floor carbon data to produce an estimate of total forest system carbon. Total carbon stocks for the old-growth and second-growth stands (sums of above- and belowground data) were 257.4 and 220.9 Mg · ha ‾1 respectively. These data will be very useful in determining forest soil carbon stocks for young and old stands within the region.