Impacts of oak-focused silvicultural treatments on the regeneration layer nine years post-treatment in the southern Appalachian Mountains of North Carolina
Beasley, Christen Marie
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Oaks (Quercus spp.) are an important part of the forested landscape in the eastern United States. Although oak is increasing in standing volume, an oak regeneration bottleneck has occurred throughout its range in recent decades. Subsequently, as oak overstory is being harvested, rarely is oak recruited into the overstory to maintain the historic dominance of overstory oak. In the absence of fire and subsequent canopy closure, mesic species have proliferated, frequently forming a dense understory, inhibiting oak regeneration success. This study was developed to determine species dynamics between oak and oak competitors in response to silvicultural treatments in the southern Appalachian Mountains of North Carolina. The treatments were: a shelterwood treatment (25-30% basal area reduction through mid-story removal with herbicides), a prescribed fire treatment (two late dormant season fires occurred over a 9-year period), a shelterwood and burn treatment (prescribed fire 3-5 years following 30-40% basal area removal), and an unmanaged control. To determine treatment impacts on the regeneration layer, importance value and stems ha-1 were calculated at the species group and individual species level 0- and 9- years post initial treatment. A principal component analysis and an analysis of basal area by treatment 0- and 9-years post-treatment were used to determine the influence of site-specific characteristics on regeneration layer response. The greatest relative increases in importance values were 1401% and 2995% for the red oak group and yellow-poplar (Liriodendron tulipifera), respectively, in the shelterwood and burn (SWB). Change in all species groups were predominantly influenced by the smallest size-class (<0.6 m tall), with the exception of northern red oak (Q. rubra) and yellow-poplar in the SWB. The SWB significantly reduced importance values of all shade tolerant species groups and was the only treatment to decrease red maple (Acer rubrum) importance value and density over the study years. The prescribed fire (RXF) treatment increased red oak group importance value, while simultaneously decreasing yellow-poplar importance value and increasing red maple importance value. Changes in the red oak group in the SWB and the RXF were driven by northern red oak and scarlet oak (Q. coccinea), respectively. Treatments do not appear to change the competitive status of the white oak group. Elevation was closely associated with the red oak group. Yellow-poplar importance value increases, white oak group importance value increases, and site index were closely associated. Decreases in basal area were greatest in the SWB, and the SWB was the only treatment to significantly decrease overstory basal area. The RXF and SWB treatments improved the competitive status of only some oak species, but modifications to these treatments may result in better control of yellow-poplar and red maple competition, further improving oak's competitive status. Site specific factors such as elevation and site index may have impacted the regeneration layer response to treatments.
General Audience Abstract
Oak-hickory (Quercus and Carya spp.) and oak-pine (Quercus and Pinus spp.) forest types occupy approximately 57 million and 11 million hectares of forestland in the eastern United States, respectively. Oaks are considered ecological and economic keystone species throughout the eastern U.S and maintenance of this genus in eastern U.S. forests has been a primary regional focus for decades. Historic disturbance regimes are estimated to have been much different than they are today. Fire was a common disturbance mechanism prior to fire suppression in the early 20th century. Frequent fires maintained much of the oak component historically. In the absence of fire, the species found in the understories of mature oak stands are commonly mesophytic species, such as yellow-poplar (Liriodendron tulipifera L.) and red maple (Acer rubrum L.). Over the last several decades, research has been conducted to investigate the impacts of treatments targeting the promotion of oak regeneration, but results have been varied and valuable long-term studies are rare. To determine the effects of treatments on the regeneration dynamics of oak and its competitors, four treatments were compared in the southern Appalachian Mountains. Treatments included a control, shelterwood harvest (SW), prescribed fire (RXF), and a shelterwood and burn (SWB). Stand structure and composition were monitored over a 9-year period post-treatment. Overall, results indicate the shelterwood and burn treatment has the greatest potential to improve the competitiveness of the red oak group in the regeneration layer, but yellow-poplar competition in the shelterwood and burn will need be addressed, considering its large increases in this treatment. Although increases in the red oak group were not as great as increases in the RXF treatment compared with the SWB, fire does show promise as a method to increase oak regeneration success. Changes in red oak group importance value varied with elevation, emphasizing results of treatments can be affected by site characteristics. Treatments were not successful at enhancing the competitive status of white oak (Quercus alba L.). Silvicultural treatments can be used to improve the competitive status of oak on sites in the southern Appalachian Mountains, but close monitoring of species dynamics throughout the rotation are needed to ensure long-term oak success.
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