A Century of Disturbance and Dynamics During the Establishment of White Oak (Quercus alba) Dominance in Forests of Southeastern Ohio

Date of Award


Degree Name

M.S. in Biology


Department of Biology


Ryan W. McEwan


The structure and composition of forest ecosystems throughout eastern North America has been determined by historical disturbances and successional processes. The white oak group (Leucobalanus) was an important species culturally for Indigenous Peoples of eastern North America for hundreds of years and has been highly valued by European colonizers of the 18th and 19th centuries. The white oak tree (Quercus alba) is a geographically widespread species in eastern North America that has historically been a forest dominant. In addition to popular human uses, Q. alba acorns are an important resource for wildlife. Over the past century, despite being a canopy dominant, Q. alba along with other oaks have exhibited a striking lack of regeneration and recruitment into the canopy across much of its range. This regeneration failure has been associated with a dramatic increase in the importance of shade-tolerant maple species (Acer spp.). A transition from oak-to-maple dominance could have largescale effects on biodiversity, wildlife, and soil characteristics. A variety of explanations for this oak-to-maple dominance shift have been offered in the scientific literature, predominant among these is the multiple interactive drivers hypothesis that asserts historical oak dominance was created by the interaction of multiple disturbance processes. Much remains unknown about the causes of oak-to-maple dominance shift and the multiple drivers hypothesis has not been fully vetted. In this Thesis I sought to examine factors that led to formation of Q. alba dominated forests over the past century by focusing on tree-ring analysis in forests of southwestern Ohio. These forests are near the geographic center of the Q. alba range and are broadly characteristic of the ecology in oak forests of eastern North America. I examined cross section samples of Q. alba (n = 62), chestnut oak (Q. montana) (n = 2), and shagbark hickory (Carya ovata) (n = 1) trees to assess (a) long- term fire history in the site and (b) patterns of growth suppression and release that would indicate forest disturbance over the past 100 years. Fire history reconstructions had been previously accomplished. I measured tree-rings on all the samples and then applied release detection techniques designed to detect canopy disturbance that allowed light to penetrate beneath the forest canopy. I predicted (P1) that oak seedlings will have established in open conditions as evidenced by rapid growth in their first decade. Once established, these stems had hypothetically would have utilized release from shade associated with disturbances that create gaps in the canopy to advance in dominance and ultimately reach canopy status. Therefore, I predicted (P2) that oak stems would experience multiple release events prior to canopy dominance. Finally, because we know that anthropogenic fire suppression limited fires in the site after approximately 1930, I predicted (P3) a striking divergence in the two types of disturbance, with fires abruptly ending and gap dynamics occurring occasionally throughout the chronology. Evidence of high light environment establishment for oak saplings was mixed as approximately half of the samples were gap-origin (equivocal support for P1). I found strong evidence that oak trees utilized canopy gaps during canopy accession (affirming P2) as approximately 83% of stems exhibited at least one release and most stems experienced at least two release events. I also found strong evidence of a divergence in the two disturbance processes (affirming P3) as fire scars indicating historical fires occurred in the site from approximately 1880 to 1940 and then ended abruptly, while release events were consistently recorded throughout the chronology. These results support a multiple interacting disturbances framework for oak forest establishment. Specifically, I found strong evidence of historical fires during the initial establishment of the stands followed by releases that were non-fire associated during which Q. alba trees were presumably moving into the forest canopy. These results suggest that management for oak forests could use prescribed fire as a way to initiate a strong pool of oak saplings followed by individual tree or small patch cutting to add light to the forest floor and promote those saplings into a position in the canopy. Understanding long-term dynamics of oak forests is a pressing scientific concern and my data indicate that future work focusing on the interaction of disturbance processes could be a fruitful area of scientific research.


Biology, Ecology, Environmental Management, Environmental Science, white oak, forest management, canopy gaps, fire history, Quercus alba, Vinton County Experimental Forest, Southeast Ohio, iron furnace, oak-fire hypothesis, dendrochronology, tree rings, growth patterns

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