Masters Theses

Date of Award

8-2004

Degree Type

Thesis

Degree Name

Master of Science

Major

Forestry

Major Professor

David S. Buckley

Committee Members

Wayne K. Clatterbuck, Arnold M. Saxton, Scott E. Schlarbaum

Abstract

The success of northern red oak (Quercus rubra L.) in the oak-hickory forest type and its growth and development into the overstory is of great concern due to the value of this species as a source of forest products and mast for wildlife. There is a general consensus that rapid oak seedling height growth occurs above certain threshold levels of light, soil moisture, and nutrients. If these specific levels and the relative importance of competition between northern red oak (NRO) seedlings and other individual plant species can be determined, then the implementation of more precise management practices that promote rapid NRO seedling height growth and more cost-efficient competition control treatments could be developed. The detection of genetic family differences among artificially regenerated NRO seedlings could also have future applications in advancing the competitive ability of NRO in the field.

This study had three objectives. The first objective was to identify light, soil moisture, and nutrient levels in the immediate vicinity of NRO seedlings that lead to rapid height growth. The second objective was to establish which plant species are the most important competitors limiting these resources and thus the height growth and survival of NRO seedlings. The third objective was to identify potential genetic family differences among the NRO seedlings used in this experiment.

This study was conducted on moderately productive sites in mature oak-hickory forests on the University of Tennessee Forestry Experiment Station at Oak Ridge in east Tennessee. A randomized complete block design was used, and the dependent variables were height growth and percent survival for all NRO seedlings. Six treatments were randomly assigned to equally sized plots within three blocks (10 hectares per block) during the summer of 2002. Blocking was based primarily on aspect, but also included stand structure, forest composition, and landscape position. In order of decreasing canopy cover, the treatments were: uncut (Control), 50% basal area retention (BAR), 25% BAR, 12.5% BAR, commercial clearcut (CCC), and silvicultural clearcut (SCC). Sixty premium artificially regenerated NRO seedlings from 18 different half-sibling families were then planted within each treatment in mid April of 2003.

Significant differences in mean percent full photosynthetically active radiation (PAR) existed between nearly all treatments. The Control treatments received the lowest percent full PAR level at 3.84 percent and the SCC received the most at 86.67 percent. The north facing block was significantly different from the south facing and ridge top blocks receiving almost 8 percent less PAR on average. Soil moisture levels were not significantly affected by treatments or blocks. Greater than normal precipitation levels during the 2003 growing season may have influenced soil moisture and seedling performance. Macronutrient levels were not significant in explaining NRO performance in this study.

Total height growth was noticeably greater (by more than 12 cm on average) in the Controls than all other treatments. Mortality was also highest in this treatment (10 percent) and most likely due to heavy shade. Very little mortality (<2 percent) occurred in all other treatments combined. Fireweed (Erechtites hieracifolia L.) and horseweed (Erigeron canadensis L.) were the most abundant herbaceous species overtopping the NRO seedlings. They occurred mainly in the 25% BAR, 12.5% BAR, CCC and SCC totaling 7, 5, 12, and 5 percent of the total cover respectively. Yellow-poplar (Liriodendron tulipifera L.) and red maple (Acer rubrum L.) were the most abundant woody species in this study.

Ranging from 17 cm to 29 cm, mean height growth differed significantly between genetic families. No differences in survival were detected between families. However, three genetic families had 100 percent survival and the family with the greatest mortality had 9 percent mortality.

Multiple regression was conducted using the backward selection technique to determine the best model for predicting NRO seedling height growth in this study. The best model had nine independent variables for predicting NRO seedling growth with an R2 of 36.37 percent. Initial seedling height after planting and percent full PAR were the most significant variables in the model. PAR and initial seedling height both had a negative relationship with first year height growth. Initial root collar diameter was also significant and had a positive relationship with first year height growth. Potential woody competitors such as redbud (Cercis canadensis L.) and blackgum (Nyssa sylvatica Marsh) also proved to be significant in predicting NRO seedling height growth. Both species had a positive relationship with seedling growth in the 51-150 cm size class.

Based on these first year results, greater height growth appears to be associated with less sunlight, although this seems to be the result of etiolation in the Controls. Yellow-poplar and red maple, which were the most abundant competitors in this study, do not appear to currently have any effect on NRO seedling height growth. Redbud and blackgum, on the other hand, seem to be possible indicators of good sites for NRO seedling height growth. Shorter seedlings with thicker root collar diameters exhibited more height growth than seedlings that were taller or had smaller root collar diameters.

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