Field sampling was conducted quarterly from March 2011
through March 2012 for a total of five sample periods (March,
June, September and December 2011, and March 2012) at the
Long-Term Soil Productivity (LTSP) site in Davy Crockett National
Forest near Groveton, TX, USA (31060 32.4800N, 95090 59.1500W)
(hereinafter ‘‘Groveton LTSP’’). The climate is subtropical with a
mean annual temperature of 19.1 C and mean annual precipitation
of 1135 mm (1981–2010) that is bimodal, with peaks in
May–June and October (Fig. 1). Topography is nearly flat with
slopes of 1–3% and elevation ranging from 101 m to 110 m. Soils
across the study area are uniform (fine-loamy siliceous, thermic
Oxyaquic Glossudalf in the Kurth series) and developed in loamy
coastal plain sediments of the Yegua and Whitset geological formations.
The A-horizon occurs at 0–15 cm, while the E-horizon
extends from 15 to 50 cm.
The Groveton LTSP treatment plots were established in 1997 in
accordance with the parameters specified by the LTSP program
(Powers, 2006) which consists of three harvest intensities (bole
only, whole tree, and whole tree + forest floor removal) and three
levels of soil compaction (none, intermediate, and severe) in
factorial combination (nine treatment combinations) replicated
three times on 0.4 ha plots. At the time of harvest, stands were
55–80 years old and consisted primarily of P. taeda L. with scattered
hardwoods (<10%). A feller buncher and skidder were used
for harvesting on the compacted plots, while the non-compacted
plots were hand-felled, with trees lifted off the plots with a loader
(Rick Stagg, USDA Forest Service, personal communication). A 9Z
pneumatic-tired roller (W.E. Grace Manufacturing Co., Dallas, TX,
USA) loaded to 2.4 Mg m1 and 4.2 Mg m1 for the moderate and
severe compaction, respectively, was towed by a farm tractor and
rolled over the soil a total of six times (three passes in one direction
and three passes in a second direction perpendicular to the
first passes) (Rick Stagg, USDA Forest Service, personal communication).
Forest floor removal was accomplished by hand raking
all aboveground organic matter from the whole tree + forest floor
removal treatments plots. Containerized P. taeda L. seedlings of
10-half sib families from US Forest Service seed orchards in
Louisiana, Mississippi, and Texas were hand planted on a
2.5 m 2.5 m spacing. Each of the 27 treatment plots was split
for glyphosate herbicide treatment that was applied once per year
for five years following harvest.
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