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Vol. 15, Special Issue 9
Overstory Species Composition, Structure, and
Conservation Challenges of a Mature, Natural-Origin Pine
Stand After Decades of Management
Don C. Bragg*
Abstract - This study provides a preliminary assessment of 4 compartments on the Crossett
Experimental Forest (CEF) being restored to old-growth-like conditions. After being
partially cleared for agriculture or lumbered in the late 1910s, Compartments 1, 2, 11, and
12 were included in a combination of pulpwood-thinning and uneven-aged cutting-cycle
studies for the next 50 y. Today, these compartments are overwhelmingly comprised of large
Pinus taeda (Loblolly Pine) and Pinus echinata (Shortleaf Pine). A mixture of 22 other species
comprise the remainder, primarily in small-diameter stems. Of the 139 ring-counted
trees, similarly-sized Shortleaf Pines were significantly older than Loblolly Pines. Current,
live-tree oven-dry biomass in Compartments 1, 2, 11, and 12 approaches 200 Mg/ha, or
approximately twice that historically reported for old-growth pine. The effects of decades
of conventional silviculture, the limited occurrence of fire, and a lack of pine (especially
Shortleaf Pine) regeneration are conservation concerns related to this long-term study.
Since the clearing of the virgin timber in the early 20th century, silvicultural
practices have been the main factor in determining forest composition, structure,
and dynamics across most of the southeastern US. With its suitable soils, abundant
moisture, long growing season, and predominantly privately owned forests,
it is not surprising that the southeastern US is now the largest timber-producing
region in the world (larger than any other single nation), producing about 12% of
the global supply of industrial roundwood and 63% of US timber-growing stock
removals (FAO 2014, Oswalt et al. 2014). Much of this production was initiated
after 1950 and has increased in recent decades following reduced harvest
of old-growth conifers from the western US and the expansion of increasingly
intensively managed southern Pinus (pine) plantations (Carter et al. 2015, Wear
and Greis 2002).
Pine plantation cover in the southeastern US has grown from an estimated
750,000 ha in 1952 to almost 16 million ha in 2010 (~19% of all forests), with
concurrent declines in natural-origin pine and oak–pine stands (Hartsell and Conner
2013). The Upper West Gulf Coastal Plain (UWGCP; Klepzig et al. 
labeled the UWGCP as their “Middle Gulf-West section”) of southern Arkansas,
northern Louisiana, and northeastern Texas has experienced this transformation
to an even greater degree, with about 23% of the 8.5 million ha of forestland now
*Southern Research Station, USDA Forest Service, PO Box 3516 UAM, Monticello, AR
Manuscript Editor: Jerry Cook
Proceedings of the 6th Big Thicket Science Conference: Watersheds and Waterflow
2016 Southeastern Naturalist 15(Special Issue 9):16–41
2016 Vol. 15, Special Issue 9
in planted pine (Klepzig et al. 2014). Although the loss of natural-origin upland
forests is expected to continue well into the future, natural pine-dominated forests
are still forecast to cover much of the UWGCP (Klepzig et al. 2014), and they
offer opportunities for certain ecosystem services otherwise unavailable from intensively
managed, short-rotation Pinus taeda (Loblolly Pine) plantations (e.g.,
Bragg et al. 2014, 2015). Indeed, numerous public-land management agencies,
non-governmental organizations, and some private landowners are actively seeking
alternatives to southern pine-plantation silviculture that protect elements of mature
forest systems with the promise of some timber returns to help cover management
and restoration expenses (Guldin 2011).
However, those interested in a treatment regime that improves ecosystem services
beyond timber production and restores certain conditions found in old-growth
Loblolly and Pinus echinata (Shortleaf Pine) forests have few guiding principles
available to direct their efforts. Designs for this type of alternative silviculture have
precedent: researchers have been working on encouraging the development of oldgrowth-
like characteristics in second-growth stands of other forest types, such as
Pinus palustris (Longleaf Pine, Mitchell et al. 2006, Moser et al. 2002), western
conifers (Baker et al. 2007, Lindh and Muir 2004), and northern hardwoods (Fassnacht
et al. 2015). Fortunately, natural-origin Loblolly and Shortleaf Pine-dominated
upland forests respond well to a range of silvicultural options (Guldin 2011,
Schultz 1997), suggesting that a management strategy to enhance old-growth-like
characteristics in this forest type is possible.
Restoration success depends on both initial stand conditions and how the
second-growth Loblolly–Shortleaf Pine forest responds to the applied treatments.
As suggested by recent reviews (e.g., Stanturf et al. 2014a, b), there are a number
of guiding principles of silviculturally based ecosystem restoration that can help
provide a treatment framework. Key to this framework are the development of
fundamental knowledge of the system to be restored, articulation of the desired
future outcomes, and the identification of the silvicultural treatments and natural
processes available to achieve this outcome. The research presented here represents
the first step of this process—the description of a mature, natural-origin pinedominated
stand in the UWGCP of southeastern Arkansas, including an assessment
of past management practices and a number of likely conservation challenges that
may affect restoration treatments. Full nomenclature, including authorities, for all
species mentioned is provided in Table 1 and Appendix A.
The work for this study was conducted in Compartments 1, 2, 11, and 12 of
the Crossett Experimental Forest (CEF), located in southern Ashley County, AR
(Fig. 1). The study area is part of a long-term research project to evaluate a range
of silvicultural treatments designed to accelerate and enhance old-growth-like
attributes in second-growth pine-dominated forests of the UWGCP. These northeastern-
most compartments (centered at 33°2.65'N, 91°55.2'W) occupy 64.8 ha, or
just under 10%, of the 678-ha CEF.
Vol. 15, Special Issue 9
Geologically, this part of the UWGCP consists primarily of the late Quaternary
Prairie Terrace complex, composed of alluvium from the Arkansas, Mississippi,
and Ouachita rivers deposited ~110,000–210,000 years ago (Saucier 1974, Shen
et al. 2012). These older terraces are capped across most of the region with late
Figure 1. Location of the old-growth pine-management study (Compartments 1, 2, 11, and
12) on the Crossett Experimental Forest in southeastern Arkansas.
2016 Vol. 15, Special Issue 9
Pleistocene loess (Heinrich 2008, Rutledge et al. 1996, Shen et al. 2012). The
landforms of the CEF consist primarily of gently rolling hills and relatively level
flatwoods incised by meandering ephemeral stream channels. Compartments 1,
2, 11, and 12 gradually rise in elevation with increasing latitude; the lowest elevations
are ~40 m ASL in the south, and the highest are in the north and east (to
47 m ASL). The somewhat poorly drained soils of the CEF formed primarily in
the 0.5- to 1-m-thick loess that covers most of the area. The tops of the ridges are
Bude silt loams, the side slopes consist primarily of Providence silt loams, and the
immediate streamside areas (Holocene terraces) are Arklabutla silt loams (Gill
et al. 1979). Low (typically, less than 1 m tall), circular (often 10–20 m wide), naturally
formed “prairie” or “pimple” mounds are common across the CEF, including in
the study compartments.
Climatically, the Crossett area is in the humid subtropical zone and receives on
average 1445 mm of precipitation, primarily in the form of rain (1981–2010 climate
norms; NOAA 2015). Precipitation tends to be fairly evenly distributed across
the year, with somewhat more from December to February, and slightly less from
August to September). Average January and July maximum temperatures are 12.4
°C and 33.2 °C, respectively, and average January and July minimum temperatures
are -0.6 °C and 20.0 °C, respectively. Ashley County has a growing season of approximately
240 d per year (Cain and Shelton 2001).
Current forest composition on the CEF is predominantly Loblolly Pine, with
lesser amounts of Shortleaf Pine, Liquidambar styraciflua (Sweetgum), Quercus
alba (White Oak), Quercus falcata (Southern Red Oak), Quercus nigra (Water
Oak), Acer rubrum (Red Maple), Nyssa sylvatica (Blackgum), Ulmus alata (Winged
Elm), and numerous other tree species. Understory vegetation is similarly diverse,
with many woody shrubs (e.g., Callicarpa americana [American Beautyberry],
Rhus glabra [Smooth Sumac]), lianas (e.g., Vitis rotundifolia [Muscadine], Gelsemium
sempervirens [Carolina Jessamine], Toxicodendron radicans [Poison Ivy]),
briars (e.g., Rubus spp. [raspberries, blackberries], Smilax spp. [greenbriars]),
forbs, graminoids, and ferns. A number of invasive plant species are also found on
the CEF including Ligustrum sinense (Chinese Privet), Lonicera japonica (Japanese
Honeysuckle), Lygodium japonicum (Japanese Climbing Fern), and Triadica
sebifera (Chinese Tallow-tree).
Determining the management history of the study area
I conducted this research on a second-growth forest that arose following the cutting
of the virgin pine between 1915 and 1920 (Darling and Bragg 2008, Reynolds
1980). The timber cut by the Crossett Lumber Company was a relatively even mixture
of old-growth Loblolly and Shortleaf Pine, with a minor and varying hardwood
component (Chapman 1913, Reynolds et al. 1984). Unfortunately, there are no detailed
accounts of the study compartments, including their cutting history, prior to
the establishment of the CEF. However, I consulted a number of historical records
of the general area to provide an assessment of forest conditions prior to 1934.
Vol. 15, Special Issue 9
After the CEF opened, this 64.8-ha block was managed using various silvicultural
techniques, primarily a range of uneven-aged treatments. In the 1990s, Compartments
2 and 12 were designated as a part of an old-growth pine-management
study, but no major management interventions were conducted. Compartment 1
was added to this research in 2005, followed in 2006 by Compartment 11. Over the
past 15 years, management has focused on ensuring overstory consistency between
the different compartments, with treatment decisions determined based on a longterm
strategy of managing for old-growth-like conditions (Bragg 2004a). Since
2000, only 1 harvest, a thinning from below to 12–16 m2/ha of basal area, has been
conducted in the study compartments; several prescribed burns (in all compartments)
and a limited amount of understory brush mowing (Compartment 12 only)
have also been undertaken.
Plot establishment and field measurements
With CEF staff, I established permanent plots in 2014 to act as the standard
inventory locations for this long-term study. Twelve circular, 0.05-ha (radius =
12.62 m) plots were systematically installed along each of 12 transects, with transects
spaced 60 m apart. To ensure that sample plots would not overlap and good
coverage of the stand was provided, none of the 144 overstory-sample plots were
spaced closer than 60 m along each transect. Each plot was also located at least
48 m from any compartment border to minimize edge effects, and a metal barbedwire
spacer was inserted into the ground at plot center to permanently monument
I identified to species all live trees >10 cm in diameter at breast height (DBH;
1.37 m above ground line) and recorded their diameter to the nearest 0.1 cm. I
determined stand-level estimates of stem frequency and basal area by summing all
individual live-tree records (1198 total) across all 144 plots standardized to a per
hectare basis. This study sought to emphasize current mid- and overstory structure
and composition; I did not evaluate regeneration (stems ≤ 10 cm) of any species.
The understory in these compartments is predominantly mixed hardwoods, with
very few pines. I also identified, counted, and measured the diameters of standing
dead trees (snags) >10 cm DBH.
Pine age-structure for these compartments was estimated using a randomized
subsample. I cored at breast height the sound (i.e., not hollow or decayed), live,
overstory pine nearest to plot center (139 of 144 plots had usable overstory pines)
regardless of species and counted the number of rings in the field. These ring counts
are only approximations of age because I did not conduct cross-dating. The pines
in the current study were cored at a different point along the bole and did not share
the same stand-development history as the nearby Farm Forestry Forties described
by Bragg and Guldin (2015); thus, I did not apply their the pine-age adjustment factor.
Nevertheless, the age estimates for these specimens are still probably within 5
y of the true age. DBH/ring-count relationships were fit for Loblolly and Shortleaf
Pine using ordinary least squares (OLS) linear regression and compared the differences
between the slopes and intercepts of these species-based equations using a
Student’s t-test (α = 0.05; Zar 1984).
2016 Vol. 15, Special Issue 9
Stand-level biomass calculations
For this paper, I determined all stand-level biomass values by calculating individual
live-tree biomass, subsequently scaled to a per-hectare basis, using the
model and coefficients of Chojnacky et al. (2014):
BAG = (eb0 + b1 ln[DBH]) / 1000 
where BAG is total aboveground oven-dry biomass (in Mg) for all stems >10 cm
DBH and b0 and b1 are species-based or species-group–based regression coefficients.
Belowground oven-dry live-tree biomass (also in Mg) was adapted from the
relationship developed by Enquist and Niklas (2002):
BBG = (BAG / 3.88)0.9803922 
I determined total oven-dry live-tree biomass by summing BAG and BBG. To supplement
data from an existing review of the literature (Bragg 2012b), I undertook
a new biomass analysis using cordwood data from a historical inventory report
(Cruikshank and Wheeler 1937) for uncut old-growth forests across the UWGCP.
This analysis assumed that 1 cord of pine yielded 2.55 m3 of green wood (470 kg/
m3 dry wt), and 1 cord of hardwood yielded 2.27 m3 of green wood (570 kg/m3 dry
wt) (conversion ratios adapted from Fonseca ). I calculated belowground
biomass using equation 2. The cordwood volumes did not include branch and foliar
biomass; thus I added a fixed adjustment of 25% to the aboveground biomass
calculation because separate analyses (data not shown) using several different approaches
to component ratios (e.g., Gonzalez-Benecke et al. 2014, Jenkins et al.
2003) have suggested that branches and foliage contribute between 20% and 30%
of total aboveground biomass, depending on tree size.
This part of Ashley County has been utilized by humans for millennia, primarily
as a source of game and botanical resources. Archeological evidence of prehistoric
Native American use of the lands that would eventually become the CEF dates to
at least 10,000 y ago, with periodic occupation and utilization fluctuating during
the intervening years. At first European contact (circa 1542), the settlements and
farms of the agriculturally oriented Mississippian culture were concentrated along
the floodplains of the major waterways rather than upland sites (Gibson 1983, Jeter
and Early 1999). By the time of the 1803 Louisiana Purchase, Quapaw Indians had
wrested control of this region from the Tunican and Koroa tribes, and it was the
Quapaw who ceded the land to the US government in an 1818 treaty (Sabo 1992).
Although it was probably not farmed, much of the pine-dominated upland in the
UWGCP experienced fires deliberately set by Native Americans to improve hunting
and foraging conditions. Centuries of frequent fire helped establish and maintain
pine dominance in an area that would otherwise have succeed to hardwood forests,
and it is likely that this pyrogenic regime was a factor in the historical prominence
of Shortleaf Pine across much of the UWGCP (Bragg 2002, 2008).
Vol. 15, Special Issue 9
The interior uplands of Ashley County remained largely unsettled by Euroamericans
until the mid-1800s; an 1842 plat map of the area showed only a single road
passing through the lands that became the CEF, and no settlers are documented
(Bragg 2012a). Between 1850 and 1860, Euroamerican settlement rapidly expanded
across the area (Bragg 2004c). Although the first formal land patents for the eventual
CEF property were not filed until 1861 (Bragg 2012a), other documentary evidence
indicates that settlers had started clearing some of the virgin timber for crops by
1853. For example, Russell R. Reynolds described an old-field stand of pine in
Compartment 1 (Fig. 2) located at one of the earliest permanent photographic points
on the CEF. In his captions written on these photographs, Reynolds provided the
following narrative: “About 1860, this road passed through a rich farming section.
The fields have since seeded into Shortleaf and Loblolly Pine and the road has been
abandoned.” Locally, most of the upland farms that developed during the latter half
of the 1800s had failed by the early 1900s (Bragg 2012a, Darling and Bragg 2008).
The Crossett Lumber Company acquired most of the still-timbered lands between
1900 and 1920 prior to cutting them with crews from their Hickory Grove Lumber
Camp (Darling and Bragg 2008).
Figure 2. Historical road passing
through former farmlands (originally
cleared before the Civil
War), now old-field Loblolly and
Shortleaf Pine, in Compartment
1 of the Crossett Experimental
Forest, AR. Photograph #352495
from the US Forest Service archives.
2016 Vol. 15, Special Issue 9
Reynolds (1959) described most of the forests on the CEF when it opened
in 1934 as burned-over, populated with numerous, low-quality hardwoods, and
with insufficient quantities of the larger pines needed to viably manage them using
the conventional approaches available at the time. In 1937, a 100% inventory
(by 2.54-cm size classes) of pines (Loblolly and Shortleaf Pines), Southern Red
Oak, White Oak, and other hardwoods, was completed on the CEF (Reynolds
1955). According to a map developed from this inventory (Fig. 3), Compartments
1, 2, 11, and 12 were primarily natural-origin pine stands in “light condition” or
“heavy condition”. The map identified more limited areas in the study compartments
as old-field stands, ~43 y old, with a small amount of open land on the
extreme eastern edge (Figs. 2, 3). Between 1937 and the early 1950s, the old-field
e r i m e n t a l
the late 1930s
open areas in
this map reflect
l i v e s t o c k
p r o b a b l y
c o m p a r t -
of the experimental
Vol. 15, Special Issue 9
portion in the center of the study compartments was part of a pulpwood-thinning
project (Guttenberg 1954; Reynolds 1937, 1980). This thinning study had a
number of treatments that reduced the overstory significantly from the dense original
old-field stand (Fig. 4a), some of which were substantial enough to permit
the recruitment of pine seedlings (Fig. 4b).
With the exception of the old-field study blocks, Compartments 1, 2, 11, and
12 were included in a series of large-scale experiments on uneven-aged southern
pine silviculture. Eventually, the pulpwood-thinning study area was incorporated
into the uneven-aged research. To address questions regarding the implementation
of uneven-aged silviculture in southern pines, a cutting-cycle–length study was
developed in 1937. Compartments 1 and 11 were placed on a 9-y cutting cycle,
Compartment 2 was on a 3-y cycle, and Compartment 12 was on a 6-y cycle (Reynolds
1955); these harvest-return intervals were maintained until about 1970 (Cain
and Shelton 2001, Reynolds 1969). When the CEF reopened after being closed
from 1974 to 1979, most of Compartments 1, 2, and 12 were transferred into the
experimental forest’s operational management areas, and Compartment 11 was
Figure 4. Images of the 43-y-old, old-field portions of the old-growth pine management
study on the Crossett Experimental Forest, AR, taken in 1936 (a), immediately prior to the
1937 thinning, and then 6 years after treatment (b) showing the released pine overstory
and a new cohort of pine seedlings emerging from the undergrowth. Overstory trees in (a)
that are still surviving are ~120 y old today; new seedlings in (b) are now nearly 80 y old.
Photographs #352494 and #427349 from the US Forest Service archives.
2016 Vol. 15, Special Issue 9
assigned to a study evaluating the influence of stand basal-area and different burning
regimes on uneven-aged stand structure (Baker and Bishop 1986, Cain 1993).
Current overstory species composition
The 2014 live-tree inventory identified 24 native tree species on the permanent
sample plots (Table 1). Loblolly Pine was the overwhelmingly dominant species,
composing 42% of the 166.4 live stems >10 cm DBH per ha in the study area. More
significantly, Loblolly Pine represented 73% of live-overstory basal area. Shortleaf
Pine accounted for less than 5% of live stems, had numerous large individuals, and therefore,
also disproportionately contributed to stand basal area (8% of the total). A
handful of hardwoods, including Sweetgum (11% of live stems), Winged Elm (8%),
White Oak (7%), Red Maple (6%), Southern Red Oak (6%), and Water Oak (6%),
each made up >5% of overstory stems counted, but most of these trees were small in
stature and when combined, accounted for only 16% of stand basal area (Table 1).
The remaining 16 species represented only a small fraction of the stand (less than 10% of
stems and 2% of basal area), and a number of them had only a single specimen.
Table 1. Species abundance and stand density of live trees (stems >10 cm DBH) in Compartments 1,
2, 11, and 12 on the Crossett Experimental Forest, AR, in 2014. Species nomenclature from Gentry
et al. (2013).
Abundance Basal area
Count Fraction Density Fraction
Common name Scientific name (stems/ha) (%) (m2/ha) (%)
Loblolly Pine Pinus taeda L. 69.72 41.90 14.451 73.05
Shortleaf Pine Pinus echinata Mill. 7.50 4.51 1.612 8.15
Sweetgum Liquidambar styraciflua L. 17.78 10.68 0.863 4.36
Southern Red Oak Quercus falcata Michx. 9.86 5.93 0.598 3.02
White Oak Quercus alba L. 12.36 7.43 0.547 2.76
Water Oak Quercus nigra L. 9.58 5.76 0.543 2.75
Winged Elm Ulmus alata Michx. 12.78 7.68 0.357 1.81
Red Maple Acer rubrum L. var. rubrum 10.56 6.34 0.353 1.79
Black Cherry Prunus serotina Ehrh. 0.97 0.58 0.057 0.29
Sassafras Sassafras albidum (Nutt.) Nees 2.78 1.67 0.053 0.27
Flowering Dogwood Cornus florida L. 3.19 1.92 0.050 0.25
Green Ash Fraxinus pennsylvanica Marshall 0.56 0.33 0.050 0.25
Blackgum Nyssa sylvatica Marshall 1.81 1.09 0.050 0.25
Post Oak Quercus stellata Wangenh. 0.97 0.58 0.039 0.20
Cherrybark Oak Quercus pagoda Raf. 0.14 0.08 0.038 0.19
Mockernut Hickory Carya alba (L.) Nutt. ex Elliott 1.25 0.75 0.035 0.18
Eastern Hophornbeam Ostrya virginiana (Mill.) K.Koch 1.94 1.17 0.031 0.16
Red Mulberry Morus rubra L. 0.42 0.25 0.019 0.10
American Holly Ilex opaca Ait. 1.53 0.92 0.017 0.09
Willow Oak Quercus phellos L. 0.14 0.08 0.007 0.04
Black Hickory Carya texana Buckley 0.14 0.08 0.005 0.02
Slippery Elm Ulmus rubra Muhl. 0.14 0.08 0.003 0.02
Black Locust Robinia pseudoacacia L. 0.14 0.08 0.002 0.01
Eastern Redcedar Juniperus virginiana L. 0.14 0.08 0.001 0.01
Totals: 166.40 100.00 19.781 100.00
Vol. 15, Special Issue 9
Tree-diameter and basal-area distributions
Table 2 provides the minimum, maximum, and average DBH by species for the
study compartments. Quercus pagoda (Cherrybark Oak) had the highest average
DBH (58.7 cm), although this species was represented by only a single overstory
tree. Of the most common taxa, Shortleaf Pine had the highest average DBH (50.3
cm), followed by Loblolly Pine (48.5 cm). Most hardwoods were small in diameter,
averaging 10–30 cm DBH. Loblolly Pine (85.6 cm), Water Oak (80.5 cm), and
Shortleaf Pine (80.0 cm) were the only species whose maximum DBH exceeded 70
cm, a threshold sometimes used to help define types of old-growth in the eastern
US (e.g., Brown et al. 1997).
As noted earlier, Loblolly and Shortleaf Pine contributed >81% of the 19.8 m2/
ha of live-overstory basal area in the study area (Table 1). However, their contribution
to basal area was not evenly distributed. Figure 5 provides the basal-area
contributions by diameter classes for the 6 most-dominant species (Loblolly Pine,
Shortleaf Pine, Sweetgum, Southern Red Oak, White Oak, and Water Oak) plus a
group that includes all of the remaining taxa. Although Loblolly Pine clearly dominates
total stand basal area, it has only a minor presence in the understory (trees less than 10
Table 2. DBH distribution of live trees >10 cm DBH in Compartments 1, 2, 11, and 12 on the Crossett
Experimental Forest, AR, in 2014. For species with only 1 observation, only the average DBH
Minimum Maximum Average deviation
Common name n (cm) (cm) (cm) (cm)
Loblolly Pine 502 10.4 85.6 48.5 16.84
Shortleaf Pine 54 19.1 80.0 50.3 14.42
Sweetgum 128 10.2 61.5 22.5 10.61
Southern Red Oak 71 10.2 53.8 25.5 11.17
White Oak 89 10.2 57.9 21.1 10.87
Water Oak 69 10.2 80.5 23.3 13.53
Winged Elm 92 10.2 37.1 18.1 5.30
Red Maple 76 10.2 42.9 19.1 7.98
Black Cherry 7 15.0 45.2 25.5 10.30
Sassafras 20 10.4 22.4 15.2 3.69
Flowering Dogwood 23 10.2 20.3 13.8 3.10
Green Ash 4 11.2 45.5 30.4 16.90
Blackgum 13 10.2 34.3 17.7 6.33
Post Oak 7 15.2 27.7 22.1 5.03
Cherrybark Oak 1 - - 58.7 -
Mockernut Hickory 9 10.4 29.2 17.8 6.46
Eastern Hophornbeam 14 11.4 19.6 14.1 2.74
Red Mulberry 3 16.5 33.3 23.1 8.94
American Holly 11 10.2 14.5 11.9 1.58
Willow Oak 1 - - 26.2 -
Black Hickory 1 - - 20.8 -
Slippery Elm 1 - - 17.5 -
Black Locust 1 - - 15.0 -
Eastern Redcedar 1 - - 10.4 -
2016 Vol. 15, Special Issue 9
cm DBH) and midstory (10–35 cm DBH) and shares dominance with a number of
hardwoods to about 44 cm DBH. Shortleaf Pine is uncommon in size classes less than 40
cm DBH and only erratically present in the largest-diameter classes. The understory
of this stand is overwhelmingly comprised of hardwood species; only an occasional
oak or Sweetgum exceeded 50 cm DBH (Fig. 5).
Consistent with the basal-area results, Loblolly Pine and Shortleaf Pine contributed
the vast majority of the 199.1 Mg/ha of total oven-dry live-tree biomass
in the study compartments, 73% and 8%, respectively (Table 3). Even though most
hardwoods have higher wood specific gravity than pines, a difference reflected in
the predictive models used in this paper (Chojnacky et al. 2014), the pines were so
dominant in the largest tree-size classes, that their somewhat lower specific gravity
had little influence on total biomass contributions.
Of the 139 pines cored for age estimates, 18 were Shortleaf Pine (just under
13% of all pines), or slightly more than the ~10% of the Shortleaf Pine stem counts
compared to the overall pine sample. Although I made no attempt to ensure the
randomized sample came from across the full size- (and age-) distributions, the absence
of young Shortleaf Pine (the youngest sampled had 49 rings) compared to the
presence of multiple young Loblolly Pine (the youngest had only 11 rings) indicates
Figure 5. Per-hectare live-overstory basal area contributions by 2.54-cm DBH class for the
most dominant taxa in Compartments 1, 2, 11, and 12 on the Crossett Experimental Forest,
AR, sampled in 2014.
Vol. 15, Special Issue 9
that Shortleaf Pine has not dependably regenerated in the study compartments for
decades. Both Loblolly Pine and Shortleaf Pine were well represented in trees estimated
to be 50 y old or older, with a particular concentration of pines between 50
and 70 y (Fig. 6). The oldest cored pine was a Shortleaf Pine that had 129 rings;
the oldest cored Loblolly Pine had 121 rings. On average, Shortleaf Pines had 86.5
rings (standard deviation = 22.5 rings), and Loblolly Pine had 65.8 rings (standard
deviation = 19.3 rings). The randomized sample did not purposefully seek out the
oldest living specimens; thus, it is possible that even older pines remain in these
OLS regressions fit to DBH and ring count produced similarly trending but
statistically different lines (Shortleaf Pine ring count = 32.0746 + [0.9563 ×
DBH], adjusted R2 = 0.3257, RMSE = 18.51; Loblolly Pine ring count = 19.7166 +
[0.8592 × DBH], adjusted R2 = 0.4743, RMSE = 14.01; Fig. 6). Even though both
species had considerable amounts of variability around these trend lines, the age/
Table 3. Calculated oven-dry biomass of live trees >10 cm DBH by species in Compartments 1, 2,
11, and 12 on the Crossett Experimental Forest, AR, in 2014. Total biomass = aboveground + belowground.
Aboveground A Belowground B Total
Common name (Mg/ha) (Mg/ha) (Mg/ha)
Loblolly Pine 119.512 25.642 145.154
Shortleaf Pine 13.270 2.848 16.118
Sweetgum 7.504 1.645 9.149
Southern Red Oak 5.432 1.187 6.619
White Oak 4.783 1.047 5.830
Water Oak 5.375 1.164 6.539
Winged Elm 2.421 0.542 2.963
Red Maple 2.002 0.447 2.449
Black Cherry 0.499 0.109 0.608
Sassafras 0.315 0.071 0.386
Flowering Dogwood 0.276 0.063 0.339
Green Ash 0.509 0.110 0.619
Blackgum 0.346 0.077 0.423
Post Oak 0.284 0.063 0.347
Cherrybark Oak 0.481 0.102 0.583
Mockernut Hickory 0.240 0.054 0.294
Eastern Hophornbeam 0.173 0.039 0.212
Red Mulberry 0.154 0.034 0.188
American Holly 0.084 0.019 0.103
Willow Oak 0.058 0.013 0.071
Black Hickory 0.032 0.007 0.039
Slippery Elm 0.020 0.005 0.025
Black Locust 0.014 0.003 0.017
Eastern Redcedar 0.003 0.001 0.004
Totals: 163.8 35.3 199.1
AAfter Chojnacky et al. (2014).
BAfter Enquist and Niklas (2002).
2016 Vol. 15, Special Issue 9
diameter slopes were different between Loblolly Pine and Shortleaf Pine (t = 4.238,
P < 0.001). According to these regressions, a 50-cm DBH Shortleaf Pine would be
17 y older on average than a similarly sized Loblolly Pine (80 y old compared to 63
y; t = 4.298, P < 0.001).
Snag composition and abundance
Only 18 snags occurred within the 144 study plots, and no new species were
added to the overstory species list. The standing-dead trees included Loblolly
Pine (5 snags); Shortleaf Pine, Red Maple, Southern Red Oak, and Winged Elm
(2 snags each); and Flowering Dogwood, Green Ash, Sweetgum, Water Oak,
and Sassafras (1 snag each). Most of the hardwood snags were small (10–25 cm
DBH), while most of the pine snags were >50 cm DBH. Snag density was so low
in this stand (2.5 snags/ha in 2014) that I undertook no further analysis of this
Figure 6. Age-class structure of randomly sampled pines from Compartments 1, 2, 11, and
12 on the Crossett Experimental Forest, AR, collected in 2014 (top histogram shows the
sample distribution). Solid line is for the ordinary least squares (OLS) linear regression
through the Shortleaf Pine; the dashed line represents the Loblolly Pine samples.
Vol. 15, Special Issue 9
Similarity of study compartments to old-growth, past and present
Virtually no functional examples of open, pine-dominated old-growth forests
remain across the UWGCP to serve as a basis of comparison with the study compartments.
Available reference conditions from historical sources (e.g., Bragg 2002)
suggest that Compartments 1, 2, 11, and 12 have a number of attributes consistent
with past examples of old-growth pine forests. In addition to a substantial Shortleaf
Pine component, the study compartments are dominated by large-diameter pines in
many age classes, with only a scattering of smaller hardwoods. At just under 20 m2/
ha of live-overstory basal area, the study compartments are at the upper end of the
stand-density ranges reported in historical records for old-growth pine stands from
the UWGCP (Table 4). Unlike historical old-growth, which usually had many pines
from 150 to 300 years of age (Bragg 2002, 2010; Chapman 1913), lumbering followed
by decades of uneven-aged silviculture seem to have capped the maximum
pine age at ~130 years in the study compartments, with most (72%) overstory pines
between 50 and 90 years old (Fig. 6).
In addition to the relatively high basal area and a scarcity of old pines, the biomass
range of these compartments (nearly 200 Mg/ha) exceeds the biomass range
historically reported for old-growth pine forests in the UWGCP (Bragg 2012b;
see also Table 4). This distinction is important because some researchers have
theorized that both high basal area and aboveground live-tree biomass can serve as
indicators of certain types of old-growth, particularly when concentrated in large
individual trees (Brown et al. 1997, Held and Winstead 1975). For example, Brown
et al. (1997) used a collection of known old-growth hardwood-dominated forests
from the eastern US, with aboveground biomass between 220 Mg/ha and 260 Mg/
ha and 30% of all stems in trees >70 cm DBH, to identify potential old-growth
stands from large-scale inventory data. While these criteria may be acceptable for
mesic hardwood-dominated old-growth forests, they overstate the stand density
and biomass for fire-prone, pine-dominated systems in the UWGCP. Table 4 clearly
shows that in historical pine-dominated old-growth stands from this region, basal
area was generally 10 m2/ha to 20 m2/ha and tree biomass was 100 Mg/ha to 150
Mg/ha, or approximately one-half of that reported for contemporary examples of
mature, unmanaged, pine-dominated forests in southeastern Arkansas, including a
few remaining unrestored examples of old-growth.
The biomass estimates I derived from inventories conducted in the mid-1930s
of remaining old-growth stands within the UWGCP (summarized in Cruikshank
and Wheeler ; reference 6 in Table 4) are the most-comparable target for the
biomass management goal of the current study compartments. Although most of
the virgin pine-dominated UWGCP forests had been cut by the 1930s, Cruikshank
and Wheeler’s (1937) old-growth inventories covered hundreds of thousands of
hectares, and likely represent a reasonable estimate of the range of stand biomass
(104 Mg/ha to 163 Mg/ha in live trees, mostly from an overstory dominated by
large pines) under most circumstances in this fire-prone region. Unfortunately,
2016 Vol. 15, Special Issue 9
Table 4. Comparison of certain stand attributes of Compartments 1, 2, 11, and 12 on the Crossett Experimental
Forest, AR, with selected historical and contemporary examples of old-growth and mature
second-growth pine-dominated forests across the Upper West Gulf Coastal Plain.
Region Min Total % pine Trees % Basal % pine
and DBH biomass bio- per ha pine area basal
Source A state B (cm) (Mg/ha) mass (tph) tph (m2/ha) area Notes
1 SE AR 36.8 102.6 47.1 67.7 54.6 12.1 57.9 Old-growth, pine ridge type
1 SE AR 34.5 109.0 49.5 75.4 54.3 13.0 60.0 Old-growth, pine flat type
2 E TX 2.5 170.6 51.7 519.4 28.2 22.9 57.3 Old-growth, poorly
3 SE AR 30.5 107.2 100.0 50.0 100.0 13.8 100.0 Old-growth, pines only
4 SE AR 5.1 128.8 100.0 222.5 100.0 18.9 100.0 Old-growth, pines only
5 E TX 10.2 54.0 100.0 168.3 100.0 8.9 100.0 Old-growth, pines only
6 NE TX 12.7 130.0 91.9 n/a n/a n/a n/a Uncut old-growth
6 NE TX 12.7 104.5 53.8 n/a n/a n/a n/a Uncut old-growth
6 N LA 12.7 145.1 89.0 n/a n/a n/a n/a Uncut old-growth
6 N LA 12.7 127.4 47.8 n/a n/a n/a n/a Uncut old-growth
6 SW AR 12.7 163.2 84.4 n/a n/a n/a n/a Uncut old-growth
6 SW AR 12.7 131.9 54.4 n/a n/a n/a n/a Uncut old-growth
7 SE AR 8.9 233.5 64.1 390.4 41.1 32 69.8 Old-field–second-growth
8 SE AR 8.9 284.6 21.7 429.9 4.3 31.4 22.7 Bottomland hardwood–
Loblolly Pine old-growth
9 SE AR 9.1 224.8 48.2 349.2 16.2 28.2 51.9 Unmanaged pine–hardwood
10 SE AR 9.1 259.4 61.3 506.5 22.8 34.5 63.5 Old-field–second-growth
11 CEF AR 9.1 310.0 47.7 454.7 13.9 36.9 52.7 Reynolds Research Natural
12 SE AR 9.1 317.3 37.4 333.9 16.3 37.1 52.2 Mature pine–hardwood, oldgrowth
13 CEF AR 9.1 101.8 97.8 253.5 91.7 15.9 97.3 Average of Good and Poor
Farm Forestry Forties
14 CEF AR 9.9 199.1 72.9 166.4 46.4 19.8 81.2 Compartments 1, 2, 11, 12
ASize, oven-dry biomass, trees per hectare, and basal area derived from the following sources: 1 =
Olmsted (1902), 2 = Zon (1905), 3 = Chapman (1913), 4 = Forbes and Stuart (1930), 5 = Garver and
Miller (1933), 6 = Cruikshank and Wheeler (1937), 7 = Bragg (2004b), 8 = Heitzman et al. (2004), 9
= Bragg (2006), 10 = Bragg and Heitzman (2009), 11 = Bragg and Shelton (2011), 12 = Bragg (2013),
13 = Bragg and Guldin (2015), 14 = current study.
BRegion and state abbreviations: AR = Arkansas, LA = Louisiana; TX = Texas, E = eastern, NE = northeastern,
N = northern, SW = southwestern, SE = southeastern, CEF = Crossett Experimental Forest.
Vol. 15, Special Issue 9
these inventories lack the species and tree-size detail needed to provide the required
context; other sources (including some found in Table 4) are required to help set
specific compositional and structural objectives.
The impacts of long-term management on stand development
The study compartments had been maintained at their 3-, 6-, or 9-year unevenaged
cutting cycles for at least 29 years; this regimen had a decided influence on
current age-class structure. Of the 139 overstory pines aged during this study, 28.1%
originated prior to the establishment of the cutting-cycle study in 1937, 64.7% during
the years of the study (1937–1969), and only 7.2% since 1970 (Fig. 6). This
skewed, broadly modal multi-aged distribution differs notably from that observed
in the nearby Farm Forestry Forties (Bragg and Guldin 2015), and is considered silviculturally
“unbalanced”. The failure to achieve significant pine regeneration over
the last 45 years is largely due to decreased overstory regulation (D.C. Bragg, pers.
observ.). Lack of management activities in the CEF during the 1970s profoundly
impacted uneven-aged stand structure, with increased pine-overstory basal area
and cover by shade-tolerant hardwoods in the understory (Cain and Shelton 2001).
Harvests conducted since 1980 have focused on thinning the overstory of the study
compartments from below. Not surprisingly, the combination of a relatively continuous
overstory, coupled with a dense, hardwood-dominated understory has greatly
limited pine regeneration. Furthermore, it appears that the periodic prescribed fires
conducted in recent years have also removed some of the younger, less fire-tolerant
Loblolly Pine without improving establishment conditions sufficient to promote the
recruitment of new Shortleaf Pine.
Perhaps more surprising than the influence of past cutting cycles is the persistence
of the oldest pines in this long-managed stand. Even after nearly 80 years
of rigorous management based on cutting cycle and periodic thinning, about 12% of
the overstory pines may have originated prior to the late-1910s lumbering of the
virgin timber—including a number that germinated prior to 1900. Years ago, Reynolds
(1969:2) noted some of these old trees in his descriptions of the initial stand
conditions when the compartments were included in the uneven-aged-stand study:
“Except for a few acres of abandoned fields, the land has always been in forest …
in 1937, none of the stands had been previously managed. The pines consisted of
grown-up residuals (stems less than 31 cm DBH) from the virgin forest scattered among
second-growth trees that had seeded in after the virgin timber had been cut.” Undoubtedly,
many of the pines that had established before 1937 have been harvested,
and mortality will continue to take others, but it is apparent from this study and
others (Bragg and Guldin 2015) that uneven-aged silvicultural practices in Loblolly
Pine and Shortleaf Pine forests can retain some of the oldest size classes.
Shortleaf Pine has long been known to be less productive than Loblolly Pine
on most sites (Mattoon 1915, Mohr and Roth 1897). For example, several studies
of soils and site index across southeastern Arkansas and northeastern Louisiana
(Turner 1936, Zahner 1958) found that Loblolly Pine produced larger trees than
Shortleaf Pine at the same base ages. This pattern also appears in the age structure
of the study compartments, with Shortleaf Pines significantly older on average than
2016 Vol. 15, Special Issue 9
Loblolly Pines of comparable diameter (Fig. 6). This slower growth, though not inherently
problematic, suggests that Shortleaf Pine could have been selected against
by foresters who marked timber for harvest (Bragg 2016). This practice likely occurred
on the CEF, which did not traditionally manage for one pine species over
another for most of its history. Reynolds (1951) reported that the implementation
of uneven-aged silviculture on the CEF appeared to gradually favor Loblolly Pine
over Shortleaf Pine—a tacit recognition that marking preferences and the suppression
of fire were affecting forest development.
Conservation challenges and their management implications
There are many challenges to the conservation of the diverse and dynamic
natural-origin pine-dominated forests of the UWGCP, not the least of which is
the widespread expansion of short-rotation, intensively managed Loblolly Pine
monocultures. As a direct consequence of this conversion, one of the primary conservation
concerns is the rapid decline of Shortleaf Pine (Bragg 2016, Moser et al.
2007, Oswalt 2012), due in part to increased coverage of Loblolly Pine plantations.
However, Shortleaf Pine is also disappearing from many otherwise intact naturalorigin
forests. Presumably, biased silvicultural selection favoring Loblolly Pine,
and the absence of frequent fire that helped to maintain the historically prominent
UWGCP Shortleaf Pine component, have been the primary causes of the decline in
natural-origin stands (Bragg 2016).
Although Compartments 1, 2, 11, and 12 have more Shortleaf Pine today than
most of the UWGCP, there is some evidence for a pronounced decline within this
study area. Professor H.H. Chapman and Yale forestry students helped to inventory
some of the properties of the Crossett Lumber Company in this part of Ashley
County, and he stated Shortleaf Pine and Loblolly Pine were found “… in an almost
equal mixture …” in the virgin timber, with more Shortleaf Pine on the drier sites
(Chapman 1913:4). Reynolds et al. (1984) reported a somewhat lower fraction of
Shortleaf Pine (25%, compared to 50% for Loblolly Pine and 25% for hardwoods)
in the virgin forests of the Crossett area. The second-growth stands that arose
following the original agricultural clearing and lumbering at the turn of the 20th
century also had a significant Shortleaf Pine component—many reports list Shortleaf
Pine as 30–40% of the saw-timber volume (Turner 1936, USDA Forest Service
1933, Wackerman 1936). More locally, Guttenberg (1954) noted that the old-field
stands of the pulpwood-thinning study in Compartments 1, 2, 11, and 12 were about
80% Loblolly Pine and 20% Shortleaf Pine prior to their cutting in 1937.
A 2000 inventory conducted in Compartments 2 and 12 (then the only compartments
in this study) noted about 26% of the pine basal area was Shortleaf Pine
(Bragg 2004a). A later (2007) 100% inventory of Compartment 12 found just over
15% of the pine overstory basal area was Shortleaf Pine (D.C.. Bragg, unpubl.
data); Compartment 2 is slightly higher in elevation and more Shortleaf Pinedominated
than Compartment 12. Shortleaf Pine currently accounts for ~10% of
the pine overstory basal area in all 4 compartments (Table 1). Restoring the study
compartments to the 25–50% Shortleaf Pine overstory composition once common
Vol. 15, Special Issue 9
to the uplands of the UWGCP (Bragg 2002, 2016; Chapman 1913; Reynolds 1959;
Reynolds et al. 1984) represents a major conservation challenge, especially given
recent research suggesting that many putative Shortleaf Pine seedlings are actually
Shortleaf Pine–Loblolly Pine hybrids (Stewart et al. 2012). Fire appears to be a crucial
environmental factor in maintaining the genetic identity of both Shortleaf Pine
and Loblolly Pine. Burning tends to only top-kill young Shortleaf Pine, which can
resprout, while it kills both Loblolly Pine and Shortleaf Pine–Loblolly Pine hybrid
seedlings (Stewart et al. 2015, Tauer et al. 2012, Will et al. 2013). Because there
are as yet no mechanical or chemical treatments that can cost-effectively emulate
this selection process, the use of frequent fire to bolster the abundance of Shortleaf
Pine appears to be a potentially useful management tool.
A related conservation issue is the failure of recent management efforts to
recruit sufficient pine seedlings of either species to help ensure that these compartments
remain pine-dominated. Although not specifically inventoried for this paper,
I observed only limited pine regeneration (stems ≤10 cm DBH) across most of the
compartments. Decades of experience in uneven-aged southern pine silviculture
at the CEF have provided a reliable blueprint for achieving good Loblolly Pine
recruitment—the evidence is less convincing that this system is effective for reproducing
Shortleaf Pine in quantity. Although fire appears to be vital to retaining
significant proportions of Shortleaf Pine, it has long been considered antithetical
to uneven-aged southern pine silviculture because it kills too many pine seedlings
to ensure proper stocking, especially if stands are burned frequently enough to
control non-pine competing vegetation (e.g., Baker et al. 1996, Guldin 2011). Research
on the CEF has shown that hardwood, shrub, vine, and briar competitors are
insufficiently controlled by infrequent dormant-season fires or mechanical releases
(Cain 1993, Cain and Shelton 2002). Hence, a blended approach to pine regeneration
may be required, with locally intense treatments (including some herbicides or
mechanical removals) to control non-pine vegetation and permit pine establishment
immediately after an overstory harvest, coupled with a fire of sufficient intensity
shortly thereafter to help reduce the number of Loblolly Pine and Shortleaf-Loblolly
hybrid seedlings while simultaneously stimulating Shortleaf Pine to resprout.
Once sufficient pine regeneration has been accumulated, additional burning treatments
of understory woody vegetation could be implemented to help encourage the
development of a forb- and graminoid-dominated understory.
Managing mature second-growth forests for old-growth-like conditions presents
distinct challenges, and is made even more difficult when initial conditions
are unknown. However, this study was initiated in a stand with a reasonably welldocumented
history. The baseline data presented in this paper will help guide the
long-term restoration of these study compartments to develop old-growth-like
characteristics by providing both starting conditions and benchmarks for evaluating
success. For instance, a survey of pine age-classes found that a small portion of the
overstory dates back to before the original “big cut”, suggesting that the biological
2016 Vol. 15, Special Issue 9
legacy of the virgin forest has not vanished even after decades of silviculture
at these sites. The overstory of this Loblolly Pine-dominated stand is decidedly
uneven-aged, due largely to decades of selective cutting in the middle of the 20th
century. However, limited pine regeneration following more-recent lighter harvests
and periodic prescribed fires suggests that additional treatments will be needed to
maintain dominance of pine in the overstory and the presence of Shortleaf Pine,
which has continued to decline in prominence.
The long management history of Compartments 1, 2, 11, and 12 on the CEF has
had both obvious and subtle influences on the present-day forest that affect future
restoration efforts. As an example, even though the pine overstory represents a single
layer of dominant and codominant trees and is thus reminiscent of an even-aged
stand, this simplicity is not reflected in the pine age-structure of the study compartments.
Silvicultural practices from years ago continue to influence this stand.
Decades of selective harvesting and the absence of prescribed fire during this critical
period (1940–1970) both contributed to the decline of Shortleaf Pine and provided
better establishment conditions for Loblolly Pine. The failure to reverse this trend has
significant implications for the long-term viability of the overall restoration strategy
for these stands, and suggests further interventions are required to ensure a continued
Shortleaf Pine presence. The resulting evenly distributed, well-stocked overstory is
not conducive to regeneration of either Shortleaf Pine or Loblolly Pine, an aspect that
will need to be remedied in order to maintain pine dominance.
I thank the following people for their contributions to this effort: Jim Guldin, Kirby
Sneed, Rick Stagg, and Donovan Stone (USFS SRS); Mike Shelton (USFS SRS, retired);
Bruce Walsh (USFS SRS, deceased); and many other scientists and technicians who helped
shape the forest in which this study was conducted. Nancy Koerth (USFS SRS) and several
anonymous reviewers graciously provided feedback on earlier drafts of this article. This
article was written by a US government employee on official time, and is therefore in the
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Appendix A. Scientific names with authorities and common names of other species named
in this paper (nomenclature from Gentry et al. 2013).
Scientific name Common name
Pinus palustris Mill. Longleaf Pine
Callicarpa americana L. American Beautyberry
Rhus glabra L. Smooth Sumac
Vitis rotundifolia Michx. Muscadine
Gelsemium sempervirens (L.) J.St.-Hil. Carolina Jessamine
Toxicodendron radicans (L.) Kuntze Poison Ivy
Rubus L. Blackberry
Smilax L. Greenbriar
Ligustrum sinense Lour. Chinese Privet
Lonicera japonica Thunb. ex Murray Japanese Honeysuckle
Lygodium japonicum (Thunb. ex Murray) Sw. Japanese Climbing Fern
Triadica sebifera (L.) Small Chinese Tallow-tree