Effects of Visual Grading on Northern Red Oak (Quercus rubra L.) Seedlings Planted in Two Shelterwood Stands on the Cumberland Plateau of Tennessee, USA

Abstract

Artificial regeneration of oak has been generally unsuccessful in maintaining the oak component in productive upland forests of eastern North America. We tested visual grading effects on quality-grown northern red oak (Quercus rubra) seedlings planted in two submesic stands on the Cumberland Plateau escarpment of Tennessee, USA. Seedlings were grown for one year using advanced fertilization and irrigation protocols to increase overall size of seedlings, but large variability in size was still evident. Seedlings were divided into two grades prior to planting. The "standard" grade represented seedlings that had undergone a light culling, and the "premium" grade represented the highest quality seedlings. Seven years after planting in a midstory-removal stand, 50 percent of trees survived, growth was negligible, and seedling grade had no effect on survival and yearly growth. In a shelterwood harvest stand, premium grade seedlings had taller height and larger basal diameter (BD) (241 cm and 29.5 mm, respectively) compared to standard seedlings (201 cm and 25.9 mm, respectively), and a two-year height growth advantage was achieved by planting premium grade compared to standard grade seedlings. Competitive ability and planting shock were similar between grades, and we postulate that an exceptional drought and large size variability in both grades equalized response. While our OPEN ACCESSForests 2015, 6 3780 findings should be confirmed through additional testing, they suggest currently accepted seedling quality standards for northern red oak should be refined to improve regeneration efforts on productive sites in the eastern United States.

Effects of Seedling Quality and Family on Performance of Northern Red Oak Seedlings on a Xeric Upland Site

“…Generalized LMM with binomial distribution was used to analyze 2015 survival (1 = alive, 0 = dead) and dominance probability of the seedlings. Surviving seedlings that attained at least 80 percent of the height of the tallest competitor within the competition plot were defined as dominant [21,23,24,40]. Data were checked for homogeneity of variance and normality.…”

“…To characterize competing vegetation, a 2.6 m diameter competition plot was centered on each planted oak seedling and species, height and diameter of the tallest woody competitor within each plot was recorded in late 2015 [24,38]. This size plot was chosen because it approximates the space that a dominant or co-dominant tree occupies at crown closure [39].…”

“…Size classes did show differences in growth pattern over the eleven year study, with more locally available seedlings dying or adding little growth than the high-quality seedlings. Most other studies that have evaluated the effect of seedling size class on field performance have followed the seedlings for fewer than ten years [24,27,31,45], with the exception of [28], which evaluated performance 17 years after planting. Clark et al [24] visually graded northern red oak seedlings into two categories and found, after seven years, that mean height and diameter of seedlings in the larger size class were 40 cm and 3.8 mm greater than the small size class, however there were no differences in survival.…”

“…The importance of seedling size to early survival and growth in northern red oak (Quercus rubra L.) has been well studied [10,[21][22][23][24][25][26][27][28]. Larger oak seedlings tend to have larger root systems, which provide carbohydrates, water, and nutrients necessary to promote rapid growth, a key trait for competing with fast-growing seedlings and sprouts [10,29].…”

“…Larger oak seedlings tend to have larger root systems, which provide carbohydrates, water, and nutrients necessary to promote rapid growth, a key trait for competing with fast-growing seedlings and sprouts [10,29]. Cultural practices to develop larger, more robust oak seedlings have been developed [30], however, improvement conferred by these larger seedlings has received limited testing, most occurring on mesic sites in the southeastern U.S. [24,31,32]. Early testing (<8 years) suggests that using high-quality seedlings (sensu [30]) produced through advanced irrigation and fertilization protocols yields improved growth and competitive ability of northern red oak when planted in previously harvested stands [24,31,32].…”