Maximizing northern red oak (Quercus rubra) seedling growth to sustain oak-dominated ecosystems in East Tennessee
Barwatt, B.A. 2004. M.Sc Thesis. Dept. Forestry, Wildlife, and Fisheries, University of Tennessee, Knoxville, TN
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 torapid 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
iv
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
v
(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.
