Date of Award

Winter 12-14-2019

Degree Type

Thesis

Degree Name

Master of Science - Forestry

Department

Forestry

First Advisor

Dr. Kathryn R. Kidd

Abstract

Upland oak-hickory forests in the Ozark Mountains of northwestern Arkansas and south central Missouri were impacted by oak decline during the early 2000s. This decline event was caused by predisposing (e.g., mature, dense stand conditions), inciting (i.e., drought), and contributing (e.g., red oak borer, E. rufulus H., outbreak) factors. Immediately following onset of the decline, substantial crown dieback and tree mortality, particularly for two red oak species (northern red oak, Quercus rubra Michx. and black oak, Q. velutina Lam.), were observed. In addition, densities of advanced oak regeneration were inadequate at this time, resulting in poor regeneration potentials for oak across much of this region. Absence of regular, frequent disturbances (e.g., fire and harvesting) in these systems for an extended time period prior to the decline, had allowed mesophication (more closed-canopy, increases in more shade-tolerant, fire-sensitive species, and the resulting cool, damp conditions with less flammable fuel beds) to occur. The creation of mortality-related gaps provided an opportunity to examine the efficacy of prescribed fire as a restoration treatment in these forests. This research evaluated the effects of single dormant season prescribed fire treatments on changes in stand dynamics and oak regeneration potentials in these degraded upland oak-hickory forests two and twelve years after implementation. Changes in overstory, sapling, and seedling strata were quantified for oak compared to mesophytic competitors (red maple, Acer rubrum;

blackgum, Nyssa sylvatica; black cherry, Prunus serotina, etc.). Changes in crown health conditions (i.e., crown dieback) were quantified by species group (red oak, white oak, hickory, and other) and compared between treatments. Sapling and seedling height, diameter, and sprouting dynamics (sprouting response and sprout density) were compared among species in the dormant and no-burn control treatments.

Twelve years following the treatments oak basal area, specifically for red oak, continued to decrease in both treatments. Greater decreases were observed in the dormant than in the control treatment. Two years following treatment, red oak species also demonstrated the greatest reduction in both the no-burn control and dormant treatment, while in the control, other species increased slightly. Red oaks classified with a healthy crown condition (< 25% crown dieback) increased by 39% in the dormant treatment while the percentage classified with dead/dying crown conditions (> 95% dieback) decreased.

Twelve years after treatment, red oak (dormant: +386%; control: +167%), white oak (dormant: +80%; control: -34%), and other species (dormant +147%; control: +57%) demonstrated significantly greater increases in sapling density in the dormant treatment compared to the control. Sapling heights were greater for non-oak competitors (15 to 23 ft.) in the no-burn control prior to and two years following treatment, but were slightly greater for oaks (17 to 18 ft.) in the dormant until twelve years following treatment (oak: 13 to 17 ft.; non-oak: 17 to 18 ft.). Sapling diameter (dbh) remained relatively similar among species groups within the two treatments. Red oak (93%) demonstrated a greater rate of topkill than white oak (63%), red maple (74%), and other species (73%) two years following in the dormant treatment. Sprouting response was greater for oak species than non-oak with, ≥ 75% resprout percentage and greater density of sprouts (15 sprouts per rootstock). Seedling densities in the dormant treatment of oaks increased two (oaks: 1,482 stems/ac; non-oak: 3,480 stems/ac) and twelve (oaks: 1,093 stems/ac: non-oak: 3,822 stems/ac) years following treatment, as well as, non-oak competitors maintaining dominance. Although seedling heights for oak species were lower than that of non-oak competitors, the basal diameter for oaks was greater two (dormant oak basal diameter: ~1.8 in.; control oak basal diameter: 0.9 to 2.8 in.; dormant non-oak basal diameter: ~3.2 in.; control non-oak basal diameter: ~3.5 in.) and twelve (dormant oak: 3.3 to 4.0 in.; control oak: 2.3 to 3.6 in.; dormant non-oak: 4.1 to 4.6 in.; control non-oak: ~4.0 in.) years following treatment in the control and dormant treatment. Oak species had a greater sprout density per rootstock than non-oak competitors two years following implementation of dormant season fires, with all species groups experiencing ~100% topkill. Twelve years after the dormant season fires, oak species (red oak: 1.3 in.; white oak: 1.2 in.) had greater dominant sprout basal diameters, as well as greater height (red oak: 10.6 ft.; white oak: 10.5 ft.) than the non-oak competitors (red maple: 1.1 in and 12.3 ft.; blackgum: 1.0 in. and 8.1 ft.) for tagged seedlings.

Previous literature has shown that frequent prescribed fires can be used to increase the density of oak while reducing the amount of shade-tolerant, fire-sensitive species. Forest health disturbances along with the implementation of a single dormant season burn, reduced overall overstory basal area, while improving overall crown health conditions and increased oak sapling and seedling densities compared to pre- treatment values. Prescribed fire also favored oak species for sprouting dynamics including, percent of resprout, sprouts per clump and sprout density for both the sapling and seedling strata. Sapling density and height (lower values may be attributed to topkill and strata recruitment) of oak improved with the reduction in basal area and prescribed fire providing increased oak regeneration potentials.

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This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Available for download on Saturday, December 17, 2022

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