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FIELD STUDIES
The following paragraphs summarize five field studies recently completed
or currently being maintained and measured by the Loblolly Pine Growth
and Yield Research Cooperative.
Regionwide Thinning Study
This thinning study consists of permanent plots established at 186 locations
throughout the native range of loblolly pine. At each location, three
comparable plots were established. Each plot was randomly assigned to
a treatment category: (1) "control," (2) "light thin,"
or (3) "heavy thin". All planted pines, plus volunteer pines
and hardwoods in the main canopy, were tagged and all plots were stem
mapped. These plots were established in 1980-82 and have been remeasured
at three-year intervals since installation. At the fourth remeasurement,
second thinnings were imposed on certain plots and stem quality and
wood sample data were collected from selected trees. Final live tree
measurements, 21 years after installation, have been collected. Additional
data from dead trees and wood samples from remaining live trees were
collected at the termination of the study, which occurred in 2004.
Spacing Trials
During 1983-1984 the Cooperative installed a set of designed spacing
trials. The purpose of these spacing experiments is to provide reliable
information on optimal density for given product objectives, juvenile
growth and mortality relationships and density effects on diameter and
height growth. Three replications were established at each of four locations.
The sites are in the piedmont and coastal plain regions of North Carolina
and Virginia. Frequent measurements of height, diameter and crown dimensions
have been collected. Results from these trials have proven valuable
in structuring and formulating growth and yield models.
Regionwide Intensively Managed Plantation (IMP) Study
From 1996-1999 the Cooperative installed permanent remeasurement plots
in intensively managed loblolly pine plantations across the native range
of the species. Similar in scope and purpose to the regionwide thinning
study, these plots will provide an adequate regionwide data base for
constructing growth and yield models applicable to managed plantations
where silvicultural options such as site preparation, planting genetically
improved seedlings, fertilization and weed control have been applied.
At each location, an untreated control plot and two treatment plots
have been established. Thinning and pruning treatments are being applied
to the treatment plots at an appropriate time during stand development.
Miniature-scale Spacing Study
In the Spring of 1989, a small-scale spacing study was established on
an area adjacent to the Virginia Tech campus. The study uses the same
non-systematic design as the large-scale spacing trials established
in 1983-1984 except that the inter-row and inter-tree spacings are at
1/16 scale of the large study. Thus, the two studies should develop
in a similar manner with a small-scale "rotation" occurring
after approximately four growing seasons. The small-scale spacing trial
offers an opportunity to examine the hypothesis that typical growth
and yield relationships occurring in plots planted at operational spacings
will also occur in plots planted at very close spacings. If true, experimentation
could be conducted in small-scale and inferences made to operational-scale
levels. This would greatly reduce the time needed to conduct experiments
and test hypotheses that often require many years to complete at operational
levels. To date, two replications have been completed and root, stem,
branch and needle biomass data have been collected from sample trees.
A third replicate of this study was established on the same site in
the Spring of 2006 using clonal material. Measurement protocols will
be similar to those of previous replications. Growth measurements from
the third replicate will be compared to those of previous replicates
to evaluate the impact of clonal material on growth and development
of loblolly pine trees.
Pruning Studies
In the Spring of 2000, two pruning studies were established at two locations
in the Virginia Piedmont. The first study, called the Early Tree Pruning
(ETP) study, is designed to determine if early pruning induces an early
age of formation of mature wood in loblolly pine trees. A randomized
complete block design has been used with five treatments:
Prune half of the green crown at age 3
Prune half of the green crown at age 6
Prune half of the green crown at age 9
Prune half of the green crown at ages 3, 6, and 9
Control
Pruning treatments through age six have been applied. Measurements of
dbh, total height, height to live crown and crown width are being collected
on an annual basis.
The second study, called the Some Tree Pruning (STP) study, is designed
to determine the effect of pruning intensity on the growth of loblolly
pine trees. A randomized complete block design has been used with five
treatments:
Remove ¼ of green crown on all trees
Remove ½ of green crown on all trees
Remove ¼ of green crown on half of trees
Remove ½ of green crown on half of trees
Control
Pruning treatments were applied during the 2005-2006 dormant season
six years after plot establishment. Measurements of dbh, total height,
height to live crown and crown width are being collected on an annual
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