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2009 SOUTHEASTERN NATURALIST 8(3):445–470
Composition, Structure, and Dynamics of a Mature,
Unmanaged, Pine-dominated Old-field Stand in
Don C. Bragg1,*, and Eric Heitzman2
Abstract - This study describes the composition and structure of a mature, secondgrowth
Pinus taeda (Loblolly Pine) and Pinus echinata (Shortleaf Pine)-dominated
old-field stand. Now owned by the University of Arkansas, this 22.5-ha parcel just
outside of the city of Monticello, AR, has been protected as a de facto natural area
since the 1950s. Many of the overstory pines exceeded 75 cm in diameter at breast
height (DBH) and some have reached 100 cm. Increment cores indicated that most
of the pine overstory originated between 80 and 100 years ago, probably following
agricultural abandonment. Pine recruitment occurred somewhat gradually until
the canopy closed, after which tree species establishment became dominated by
hardwoods. Of the nearly 6000 tree seedlings/saplings per hectare in the interior of
this stand, just under 4% were pine—the under- and midstory were dominated by
shade-tolerant hardwoods. No obvious evidence of past land-management practices
remained, save the rare old stump or formerly open-grown pine or oak. Coarse
woody debris is beginning to accumulate in some portions of the stand, primarily
from the senescence of short-lived hardwoods. Comparisons with other tracts in
southern Arkansas suggest that this stand differs from other contemporary examples
of mature pine-dominated timber, with a richness in composition and structure not
apparent in managed stands of natural or planted origin.
As late as the early 20th century, many of the landscapes of the West Gulf
Coastal Plain in the southern United States were covered in old-growth pinedominated
forests (Bragg 2002, Eldredge 1952). Some of these pine systems
were open, verging on savanna, and contained large trees 200–400 years old
(Platt 1999), while others were more closed canopy, with a mixture of large
Pinus palustris Mill. (Longleaf Pine), Pinus taeda L. (Loblolly Pine), and/
or Pinus echinata (Shortleaf Pine) rising above and under midstory of hardwoods
(Eldredge 1952). Even the extensive hardwood-dominated forests of
the region often had a prominent if passing pine component (Quarterman and
Keever 1962). However, their commercial viability, the exhaustion of other
eastern forests, and improved logging and milling techniques destined the
southern pinery for exploitation (Schultz 1997).
Decades of logging, agriculture, and other intensive land practices have
dramatically reshaped the vegetation patterns of the southern United States.
Typically, the virgin forest was cleared and then the land was converted to
some form of agriculture. Over much of this region, marginal farms were
1Southern Research Station, USDA Forest Service, PO Box 3516 UAM, Monticello,
AR 71656. 2Division of Forestry and Natural Resources, West Virginia University,
Morgantown, WV 26506. *Corresponding author - firstname.lastname@example.org.
446 Southeastern Naturalist Vol. 8, No. 3
soon abandoned, and many quickly reforested into relatively dense stands
of pure pine, pure hardwood, or gradations in between (e.g., Bragg 2004a,
Quarterman and Keever 1962, Schultz 1999). During the 20th century, these
natural-origin stands matured and most were logged again (often repeatedly),
producing a landscape dominated by modified forests. Lately, forest
management has significantly intensified across most of the South, with pine
plantations replacing many stands of natural origin (Conner and Hartsell
2002). These most recent trends are not likely to slow—if anything, the pressure
to further intensify management on a stable to declining timber base is
increasing (e.g., Fox et al. 2007, Schultz 1999).
Very few mature second-growth southern pine-dominated stands have
escaped silvicultural manipulation. One such example is the Reynolds Research
Natural Area (RRNA) on the Crossett Experimental Forest (CEF)
near Crossett, AR. The overstory dynamics of the RRNA have been welldocumented
(e.g., Cain and Shelton 1994, 1995, 1996; Guldin and Baker
1984; Shelton and Cain 1999). This 32-ha stand, which had been heavily cutover
and high-graded before 1920, was reserved as an unharvested control
during the 1930s to demonstrate decreases in pine productivity when compared
to well-managed stands (Shelton and Cain 1999). Aside from decades
of fire protection and some minor salvage following limited Dendroctonus
frontalis Zimm. (Southern Pine Beetle) outbreaks in the early 1970s, this
stand has been allowed to develop virtually untouched.
However, the RRNA is far more the exception than the rule—very little
research has been done in mature, unmanaged second-growth pine stands
in the Upper West Gulf Coastal Plain (UWGCP) and few examples of this
covertype now remain. The extensive loss of older, natural-origin pinedominated
forests across the UWGCP, coupled with the rapid conversion
of whole landscapes to short-rotation, intensively managed pine plantations
will likely have important ramifications for system characteristics, including
carbon storage, community and landscape diversity patterns, endangered
species management, ecosystem services, and even local socioeconomic
well-being. For instance, changes to avian guilds have been repeatedly documented
as a function of recent silvicultural changes across the UWGCP (e.g.,
Aquilani 2006, Thill and Koerth 2005).
This study documents the composition and structure of a mature, natural-
origin Loblolly and Shortleaf Pine-dominated stand in the absence of
silvicultural manipulation. This particular stand, arising from an “old-field”
(former agricultural/pastoral land) condition, is a typical example of the second-
growth pine-dominated forest that once covered much of the UWGCP.
We compare the traits of this stand with published information from nearby
managed and unmanaged pine forests to assess the ecological implications
of large-scale conversion of forested landscapes in this region.
The study site (Fig. 1) is located in the UWGCP geographic province
on property owned by the University of Arkansas near Monticello, AR
2009 D.C. Bragg and E. Heitzman 447
(33o37'17.75"N, 91o43'31.33"W). Figure 2 shows the position of the study
area and includes a coarse-resolution covertype map with major geographic
points of reference. Only scattered records exist on the history of this particular
tract, but evidence of at least 1 old homesite, some overgrown traces,
and a few well-decayed stumps suggest the events leading to the stand seen
today. Prior to World War II, this tract was privately owned, but the area came
under federal control by 1942, with the property serving as a Women’s Army
Auxiliary Corps (WAAC) training facility before being converted to a prisoner
of war (POW) camp for Italian soldiers from 1943 until 1946 (Pomeroy
1976). The land developed for the prisoners was located to the west of the
study area (Fig. 2). After World War II, the property was deeded to the University
of Arkansas for forestry research and demonstration projects. Since
this time, much of the former Monticello POW Camp has received various
harvesting and planting treatments, with the exception of the de facto natural
area reported in this work. This 22.5-ha stand, hereafter referred to as the
POW Camp Natural Area (POWCNA), appears to have been protected from
natural and anthropogenic disturbance for most of the last 60+ years.
Elevations for most of the POWCNA range between 58 and 63 m
above mean sea level. The study area is largely comprised of Pleistoceneera
terraces, upon which are found low-gradient Calloway silt loams and
gently to steeply sloped Grenada silt loams (Haley et al. 1993, Larance et
al. 1976). The POWCNA receives an average of about 130 cm of precipitation
annually, and is dissected by an unnamed semi-permanent stream
and numerous small drains that flow only during the wettest times of the
year (typically in winter and spring). The ephemeral stream has carved a
small, steep, relatively incised (often ≥2 m deep) channel, flanked by terraces
comprised of a narrow band of Holocene alluvium (primarily Amy
silt loam). Widely scattered tip-up mounds can be found, especially along
the active stream terraces.
Figure 1. Location
of the POW Camp
Natural Area (POWCNA)
448 Southeastern Naturalist Vol. 8, No. 3
Figure 2. Configuration of the sample plot layout in the POWCNA (top) coupled with
a broad covertype distribution and geographic feature outline (bottom).
2009 D.C. Bragg and E. Heitzman 449
Before Euroamerican settlement, this region was covered by a mixture of
Loblolly and Shortleaf Pine intermingled with hardwood species, especially
along riparian corridors (Bragg 2002, 2008). The study area likely followed
a land-developmental trajectory that included being cleared 100–150 years
ago, farmed (either with row crops or pastured, or both) for years, then abandoned
and allowed to revert back to forest. Much of this historic landscape
became poorly timbered and was frequently burned until reforestation efforts
and fire control were implemented after 1930 (Bruner 1930, Reynolds
1980, Schultz 1999).
Using a series of fixed-radius plots, data on tree species composition,
stocking, and density were gathered on the POWCNA between December
2004 and May 2005. Four parallel transects spaced 80.5 m apart were established
in the POWCNA (Fig. 2). Starting along an overgrown woods road,
each transect extended due north to the northernmost edge of the university’s
property. Between five and seven 0.081-ha circular plots were established
along each transect (for a grand total of 23 overstory plots), with 80.5 m
between plot centers (Fig. 2). Each plot was at least 30 m from the boundaries
of the POWCNA to avoid edge effects caused by adjacent clearcuts. Plot
centers were marked with a piece of steel rebar and fl agged to assist in their
relocation. On these overstory plots, every live tree at least 9.0 cm diameter
at breast height (DBH) was tallied by species and DBH (to the nearest 0.1
cm) recorded. Ring counts at DBH for a subsample of 44 Loblolly and 15
Shortleaf Pines were taken with an increment corer. Because we did not
cross-date the cores, these age estimates are approximate. However, they are
a reasonable proxy for age given their broad interpretation in this paper.
Importance values (IVs) for all tree species in the mid- and overstory
were calculated using the number of stems of species i divided by the total
number of stems of all species (relative number, or RNi), the basal area of
species i divided by the total basal area of all species (relative basal area,
RBi), and the number of plots with i divided by the total possible number of
plots with all species (relative frequency, Rfi). These three values were then
averaged and scaled between 0 and 100:
IVi = 100 x ([RNi + RBi + Rfi] / 3) 
Equation 1 adjusts for the abundance and distribution of species—taxa that
are common but spatially limited will have a lower IV than those that are
as common but more evenly distributed. This approach also constrains the
infl uence of numbers or density by standardizing their quantity relative to
In addition to the plot information on tree abundance, a number of supplementary
measurements on diameter, height, age, and species occurrence
were taken on individual trees off the plots (but still on the POWCNA) to
450 Southeastern Naturalist Vol. 8, No. 3
better help describe tree and stand attributes. For instance, additional Loblolly
and Shortleaf Pines were sampled for age from outside of these plots
after the initial sample was drawn to help determine if apparent gaps in the
size or age structure were real or due to a limited sample size.
Woody understory plants were sampled using 0.0004-ha subplots nested
within each overstory plot and located at each of the 4 cardinal directions,
for a total of 92 subplots. Each plant had to be rooted within the plot to be
tallied. The woody understory was separated into 6 size classes by species.
The first 3 classes were based on height, with stems placed into individuals
15–76 cm tall, 77–137 cm tall, and >137 cm tall, but with stem <1.5 cm
DBH. Stems >1.5 cm DBH were divided into 3 DBH classes: >1.5–3.8 cm,
>3.8–6.4 cm, and >6.4–8.9 cm. These data were recorded as counts of plants,
so specific diameters within size classes are not known.
Understory IV were calculated in a similar fashion to the overstory (equation
) using their relative number (number stems of species i divided by the
total number stems from all species), relative basal area (density, in terms of
stem basal area of species i divided by the total basal area of all species) and
relative frequency (number of subplots with species i divided by the total
number of subplots for all species). Because we only had stem counts and no
cover measure for relative basal area (density) with the three smallest size
classes (A, B, and C), a diameter was assigned to each class (A = 0.004 cm, B =
0.008 cm, C = 0.025 cm) and these values were then multiplied by the number
of stems per size class to determine their contribution to density.
We were concerned that the small size of these subplots would not fully
capture the abundance of woody vines in this stand. Lianas comprised much
of the leaf cover in the midstory, yet their stems were typically tightly clustered.
Rather than using the small understory subplots, we nested a single
liana-only plot 6.22 m in radius (0.012 ha) based on the overstory plot center.
All woody vines ≥1.37 m tall rooted within this liana subplot were identified to genus or species and its DBH measured. No IVs were calculated for
the woody vines as this measure is inadequate to account for their extensive
foliar coverage in the midstory of this stand.
Coarse woody debris inventory
All coarse woody debris (CWD) falling within the 0.081-ha plots were
recorded following methodology reported in Bragg (2004b). Three classes
of CWD were tallied: logs (downed wood ≥1 m long and 10 cm minimum
diameter), snags (standing dead tree ≥2 m tall and with a minimum diameter
of 10 cm), and stumps (standing dead tree <2 m tall and a minimum of 10 cm
diameter, with a minimum solid wood volume of 0.01 m3). CWD pieces were
identified as either pine or hardwood, and the following attributes were measured:
length (to the nearest 0.03 m, if measured with a cloth tape, or 0.3 m, if
estimated with a tape and clinometer), large- and small-end diameters (to the
nearest 0.25 cm if measured with a caliper or diameter tape, or to the nearest
2009 D.C. Bragg and E. Heitzman 451
2.5 cm, if estimated for a standing snag), and decay class. Three decay classes
were distinguished: decay class 1 = freshly dead wood; decay class 2 = some
bark loss and wood decay, but piece is still sound; and decay class 3 = most or
all bark missing, wood structural integrity largely or completely absent.
CWD volume (V, in m3) for every piece of large dead wood that fell
within the overstory plot margins was determined with Smalian’s formula
V = (π[D + d] x L) / 8, 
where D represents the large-end diameter (in m), d is the small-end diameter
(in m), and L is piece length (in m). CWD frequency and volume per
hectare were extrapolated from summing each plot’s total and averaging
over all plots. Estimates of ranges and variance were determined by calculating
per hectare totals or volumes for each plot.
The POWCNA is a pine-dominated stand with emergent Loblolly and
Shortleaf rising above a dense mid- and overstory occupied largely by hardwoods.
The understory is relatively open and populated with increasingly
shade-tolerant hardwood tree species, woody shrubs, and lianas. Some small
gaps in the overstory have been opened over the years, and these are typically
rapidly occupied by dense thickets of new plant growth.
Understory woody vegetation
There were dozens of woody understory taxa, primarily the advanced
regeneration of tree species. Understory trees of prominence (Table 1) included
Sassafras albidum (Sassafras), Quercus alba (White Oak), Ostrya
virginiana (Eastern Hophornbeam), Acer rubrum (Red Maple), Nyssa sylvatica
(Blackgum), Ulmus alata (Winged Elm), Carpinus caroliniana (American
Hornbeam), Quercus falcata (Southern Red Oak), Symplocos tinctoria
(Sweet-leaf), and even a few Loblolly Pine seedlings, especially north of the
ephemeral stream. Moderate to very shade-tolerant hardwood tree species
(e.g., White Oak, Eastern Hophornbeam, Red Maple, American Hornbeam,
Cornus fl orida [Flowering Dogwood]) dominate this strata largely because
of their ability to reach larger understory size classes under this low-light environment
(Table 1). Ilex opaca (American Holly) was present in a number
of locations across the POWCNA, but only as advanced regeneration off the
There were relatively few woody understory species beyond the tree
component (Table 1). The most common shrub species found on the study
area plots included Vaccinium spp., Corylus americana (American Hazelnut),
Callicarpa americana (American Beauty Berry), and Ilex decidua
(Deciduous Holly). Vaccinium spp. dominated the IV of the understory and
were clearly the most important of the woody shrubs, with an IV (10.0) 2.5
times greater than then next highest shrub (Table 1). A number of other shrub
species were found off of the plots in other parts of the stand, including
452 Southeastern Naturalist Vol. 8, No. 3
Table 1. Average species abundance, basal area, subplot frequency, and importance values (IV) for understory woody plants (excluding lianas) in the POWCNA
near Monticello, AR.
Taxonomic group stems Stems/ha by size class codeB
RN c RBC RFC IVC
Species or genus A per ha A B C 1 2 3 (%) (%) (%) score
Shrubs 2551.5 2121.8 322.4 107.5 0 0 0 - - - -
Vaccinium spp.D 1611.5 1504.1 26.9 80.6 0 0 0 20.27 0.46 9.3 10.0
American Hazelnut (Corylus americana Walt.) 537.2 322.3 188.0 26.9 0 0 0 6.76 0.21 4.9 4.0
American Beauty Berry (Callicarpa americana L.) 161.1 107.4 53.7 0 0 0 0 2.03 0.03 3.7 1.9
Deciduous Holly (Ilex decidua Walter) 107.4 80.6 26.9 0 0 0 0 1.35 0.02 0.6 0.7
Red Buckeye (Aesculus pavia L.) 53.7 53.7 0 0 0 0 0 0.68 0.01 1.2 0.6
Rubus spp. 53.7 53.7 0 0 0 0 0 0.68 0.01 1.2 0.6
Serviceberry (Amelanchier arborea (Michx. F.) Fern.) 26.9 0 26.9 0 0 0 0 0.34 0.01 0.6 0.3
Trees 5398.8 4243.8 215.0 188.2 376.1 268.8 107.6 - - - -
Sassafras (Sassafras albidum (Nutt.) Nees.) 725.2 671.5 53.7 0 0 0 0 9.12 0.09 5.6 4.9
White Oak (Quercus alba L.) 698.3 617.7 0 26.9 26.9 0 26.9 8.78 11.05 9.9 9.9
Eastern Hophornbeam (Ostrya virginiana (Mill.) Koch.) 644.6 456.6 26.9 80.6 53.7 26.9 0 8.11 6.89 9.9 8.3
Red Maple (Acer rubrum L.) 590.9 537.2 0 0 0 26.9 26.9 7.43 14.22 5.6 9.1
Blackgum (Nyssa sylvatica Marsh.) 564.0 564.0 0 0 0 0 0 7.09 0.06 8.0 5.1
Winged Elm (Ulmus alata Michx.) 456.6 322.3 26.9 26.9 53.7 26.9 0 5.74 6.68 7.4 6.6
American Hornbeam (Carpinus caroliniana Walt.) 349.2 134.3 26.9 26.9 107.4 26.9 26.9 4.39 18.64 4.9 9.3
Southern Red Oak (Quercus falcata Michx.) 241.7 241.7 0 0 0 0 0 3.04 0.03 4.3 2.5
2009 D.C. Bragg and E. Heitzman 453
Table 1, continued.
Taxonomic group stems Stems/ha by size class codeB
RN c RBC RFC IVC
Species or genus A per ha A B C 1 2 3 (%) (%) (%) score
Loblolly Pine (Pinus taeda L.) 214.9 214.9 0 0 0 0 0 2.70 0.02 4.3 2.3
Sweetgum (Liquidambar styracifl ua L.) 188.0 26.9 53.7 26.9 0 80.6 0 2.36 13.20 4.3 6.6
Sweet-leaf (Symplocos tinctoria (L.) L'Hér.) 188.0 161.1 26.9 0 0 0 0 2.36 0.03 2.5 1.6
Flowering Dogwood (Cornus fl orida L.) 134.3 26.9 0 0 26.9 53.7 26.9 1.69 19.61 3.1 8.1
Mockernut Hickory (Carya tomentosa Nutt.) 134.3 53.7 0 0 80.6 0 0 1.69 3.27 3.1 2.7
Water Oak (Quercus nigra L.) 80.6 53.7 0 0 0 26.9 0 1.01 4.36 1.2 2.2
Black Cherry (Prunus serotina Ehrh.) 53.7 53.7 0 0 0 0 0 0.68 0.01 1.2 0.6
Cherrybark Oak (Quercus pagoda Raf.) 26.9 26.9 0 0 0 0 0 0.34 0 0.6 0.3
Hickory (Carya spp.) 26.9 26.9 0 0 0 0 0 0.34 0 0.6 0.3
Redbud (Cercis canadensis L.) 26.9 26.9 0 0 0 0 0 0.34 0 0.6 0.3
White Ash (Fraxinus americana L.) 26.9 0 0 0 26.9 0 0 0.34 1.09 0.6 0.7
Willow Oak (Quercus phellos L.) 26.9 26.9 0 0 0 0 0 0.34 0 0.6 0.3
AAll species nomenclature from Smith (1988) and Moore (1999). Totals may not add due to rounding errors.
BSize codes—for all stems <1.5 cm DBH: A = 15 to 74 cm tall, B = 75 to 136 cm tall, C = ≥137 cm tall; for all stems ≥1.5cm DBH: 1 = 1.5 to 3.8 cm DBH, 2 =
3.9 to 6.3 cm DBH, 3 = 6.4 to 9.0 cm DBH.
CRN (relative number) = 100 x (number of stems of species / total number of stems); RB (relative basal area) = 100 x (basal area of species / total understory
basal area); RF (relative frequency) = 100 x (number of subplots with species / total number of subplots for all species); IV (importance value) score = (RN +
RB + RF) / 3.
DProbably includes (in order of likelihood): Vaccinium arboreum Marsh. (Farkleberry) and Vaccinium stamineum L. (Deerberry).
454 Southeastern Naturalist Vol. 8, No. 3
Hamamelis virginiana (Witch-hazel), Aesculus pavia (Red Buckeye), and
Prunus spp. The vast majority of woody shrubs were 1 m or less in height
Woody vines were abundant in the study area, with >1000 stems/ha that
reached at least 1.37 m in height (Table 2). Vitis rotundifolia (Muscadine) and
Toxicodendron radicans Kuntze (Poison Ivy) dominated the lianas, comprising
nearly two-thirds of all stems. Greenbriers, grapes other than Muscadine,
Lonicera spp. (Honeysuckle), and Berchemia scandens (Rattan) composed
the remaining third. In the POWCNA, these lianas can grow to considerable
size—we found Muscadine and Vitis aestivalis (Summer Grape) vines >10
cm in diameter. In addition to large girth, it was not unusual for some species
of lianas (e.g., grapes and poison ivy) to grow into the highest layers of the
forest canopy, sometimes exceeding 30 m in height.
Overstory richness, abundance, and importance
The POWCNA has considerable overstory richness, with 26 tree species
>8.9 cm DBH found in the established study plots (Table 3). In addition
to these taxa, several other tree species were found in the POWCNA that
never occurred in the study plots, including native species such as American
Holly, Quercus pagoda (Cherrybark Oak), Fraxinus pennsylvanica (Green
Ash), Carya cordiformis (Bitternut Hickory), and Diospyros virginiana
(Persimmon), and taxa that were probably introduced such as Liriodendron
tulipifera (Tulip-poplar). Thus, at least 32 tree species were found in this
Loblolly Pine dominated all measures of stocking, constituting 21.1% of
the 489.9 stems/ha and 56.3% of the 34.4 m2/ha of total live tree basal area
found in the POWCNA. Loblolly Pine was the sole species found on all 23
plots, with only Liquidambar styracifl ua (Sweetgum) and Red Maple also
found on >90% of the plots (Table 3). Loblolly was over twice as important
Table 2. Woody vine abundance, basal area, and DBH distribution in the POWCNA.
Stems Basal Min. Max. Avg. Std.
Common per area DBH DBH DBH dev.
name Scientific name ha (m2/ha) (cm) (cm) (cm) (cm)
Muscadine Vitis rotundifolia Michx. 374.2 0.078 0.1 5.0 1.4 0.88
Poison Ivy Toxicodendron radicans (L.) Kuntze 263.7 0.032 0.1 5.1 0.7 1.06
GreenbrierA Smilax spp. 114.0 0.002 0.1 1.0 0.4 0.19
HoneysuckleB Lonicera spp. 110.5 0.009 0.2 2.0 0.9 0.44
GrapeC Vitis spp. 103.3 0.099 0.3 14.0 2.4 2.58
Rattan Berchemia scandens (Hill) K. Koch 39.2 0.015 0.6 3.4 2.1 0.89
Totals (per hectare): 1005.0 0.236
AProbably includes (in order of likelihood): Smilax rotundifolia L. (Roundleaf Greenbrier),
Smilax bona-nox L. (Saw Greenbrier), Smilax glauca Walt. (Cat Greenbrier), and/or Smilax
smallii Morong. (Lanceleaf Greenbrier).
BProbably includes (in order of likelihood): Lonicera japonica Thunb. (Japanese Honeysuckle)
and/or Lonicera sempervirens Ait. (Trumpet Honeysuckle).
CProbably includes (in order of likelihood): Vitis aestivalis Michx. (Summer Grape), Vitis
cinerea Englem. ex Millard (Graybark Grape), Vitis vulpina L. (Frost Grape), and/or Vitis
palmata Vahl. (Catbird Grape).
2009 D.C. Bragg and E. Heitzman 455
as the next highest species, Sweetgum (IV = 28.9 versus 12.9). The other
pine species in the stand, Shortleaf, was noticeably less common, contributing
only about 2.4% of the total number of live stems per hectare and <7.5%
of stand basal area. Shortleaf Pine’s relatively high basal area helped infl ate
its IV compared to species with similar numbers—there were 7 hardwood
species with more trees per hectare than Shortleaf Pine, yet all had lower IVs
than Shortleaf’s 4.8 (Table 3).
Non-pine species contributed the majority of live stems to the tallies.
Sweetgum alone provided 20.6%, followed by Red Maple (12.2%), White
Oak (7.3%), and Southern Red Oak (5.2%). No other single species exceeded
5% of the relative abundance, and 4 species (Juniperus virginiana
[Eastern Redcedar], Amelanchier arborea [Serviceberry], Castanea pumila
[Chinkapin], and Sweet-leaf) were represented by a single individual on the
Table 3. Species abundance, basal area, plot frequency, and importance values (IV) of mid- and
overstory trees (those ≥9 cm DBH) from the plot samples in the POWCNA.
Trees Basal Plots
per area with sp.
Common name Scientific nameA ha (m2/ha) (%) IVB
Loblolly Pine 103.7 19.36 23 28.9
Sweetgum 101.0 3.14 22 12.9
Red Maple 59.6 0.88 21 7.7
White Oak 36.0 1.00 16 5.6
Southern Red Oak 25.3 3.39 14 6.9
American Hornbeam 21.0 0.24 15 3.7
Flowering Dogwood 17.2 0.21 14 3.2
Winged Elm 15.6 0.21 14 3.1
Sassafras 15.0 0.24 8 2.3
Eastern Hophornbeam 14.0 0.16 14 3.0
Blackgum 12.4 0.29 17 3.4
Post Oak Quercus stellata Wang. 12.4 1.21 4 2.6
Shortleaf Pine Pinus echinata Mill. 11.8 2.56 11 4.8
Water Oak 10.7 0.49 11 2.7
Black Oak Quercus velutina Lam. 7.5 0.23 9 1.9
Mockernut Hickory 6.5 0.17 5 1.3
White Ash 6.5 0.22 9 1.9
Black Cherry 5.4 0.22 8 1.7
Willow Oak 2.2 0.09 4 0.8
Redbud 1.6 0.01 1 0.3
Red Mulberry Morus rubra L. 1.6 0.03 3 0.5
American Elm Ulmus americana L. 1.1 0.03 2 0.4
Eastern Redcedar Juniperus virginiana L. 0.5 <0.01 1 0.2
Serviceberry 0.5 <0.01 1 0.2
Chinkapin Castanea pumila (L.) Mill. 0.5 0.01 1 0.2
Sweet-leaf 0.5 0.01 1 0.2
Totals 489.9 34.4 249 100.0
AScientific names presented in Table 1 were not repeated here.
BImportance value (IV) = (relative number + relative basal area + relative frequency) / 3, where
relative number = (species number / total number) × 100; relative basal area = (species basal
area / total basal area) × 100; and relative frequency = (number of plots with species/sum of
plots over all species ) × 100.
456 Southeastern Naturalist Vol. 8, No. 3
overstory sample plots. As a group, hardwoods easily were more numerous
than the conifers in this stand, comprising over 75% of all live stems per
hectare in the POWCNA, yet there impact on overall importance was noticeably
less, with just under 2/3 of the total (Table 3). Sweetgum was the only
hardwood to contribute more than 10% of the total stand IV, as most were
5% or less.
Overstory basal-area and size-class distributions
Even with the relatively high abundance of hardwoods, the basal area and
importance value measures refl ect the dominance of the stand by the pines.
Sweetgum, for example, though >20% of total live stems, contributed <10%
of total stand basal area, compared to Loblolly Pine’s 56.3% of stand basal
area from roughly the same number of stems. Even Shortleaf Pine managed
to contribute 7.4% of stand basal area from only 2.4% of total stems. The
large size of the pines in the POWCNA ensured that their basal area was
substantially higher than most hardwoods, and resulted in their dominance
of the IV measured for this stand (Table 3).
Many of the overstory pines on the plots exceeded 75 cm DBH, and some
approached or exceeded 100 cm (Table 4). The largest Loblolly Pine encountered
in the entire POWCNA was located off of the plots and measured 104.1
cm DBH. The largest observed Shortleaf Pine was considerably smaller, measuring
72.4 cm DBH, but on average the Shortleaf in the POWCNA study plots
were larger in diameter than the Loblolly Pine (51.6 cm versus 45.3 cm DBH).
Loblolly and Shortleaf Pine were the only species with average diameters >45
cm, and amongst the non-pine taxa, only Southern Red Oak (37.8 cm DBH) and
Quercus stellata (Post Oak; 33.8 cm DBH) averaged >30 cm.
The POWCNA overstory stocking was dominated by hardwoods, although
these made up a minority of the basal area. Overstory hardwoods
were concentrated in the 2 smallest sets of size classes (Fig. 3b, c), and only
dominated the smallest of these (Fig. 3b). Few hardwoods were found on
these plots in the co-dominant and dominant size categories, and the largest
of these was a 72-cm DBH Southern Red Oak. However, within the POWCNA
as a whole (including areas off-plot), a considerable number of hardwood
specimens >75 cm DBH can be found, including White Oaks, Southern
Red Oaks, Water Oaks, Cherrybark Oaks, and Sweetgums (Table 4). Most
of the biggest pines in the POWCNA are the 30 to 35 m tall individuals that
emerge well above the 20 to 30 m tall hardwood canopy.
Pine age structure
Increment cores indicated that most of the pine component originated
between 60 and 100 years ago (Fig. 4). Of the original 59 pines sampled,
the oldest Loblolly and Shortleaf Pines were between 100 and 110 years old.
Ages ranged considerably, with some pines as young as 22 years old, and the
majority of stems ranging between 30 and 90 years old. The supplemental
pine age sample noticeably extended the age range of the pines. A number
of these additional trees fell in a small gap that formed approximately 50
2009 D.C. Bragg and E. Heitzman 457
years ago. Several others were collected north of the ephemeral stream in
part of the hardwood-dominated section on the east side of the POWCNA.
In this section of hardwoods, scattered overstory pines are found. However,
the under- and midstories are thoroughly dominated by hardwoods, and
the few small pines growing in this strata have been long suppressed—one
Loblolly Pine 12.4 cm in diameter had 31 annual rings at DBH and another
nearby Loblolly 18.0 cm in diameter had 37 rings. In the western section of
hardwoods just north of the intermittent stream, an 85.3-cm-DBH Loblolly
Pine was cored that had at least 120 rings, and may have exceeded 130 years
old (the rings near the pith were decayed and did not extract from the tree).
Table 4. Diameter at breast height (DBH) distribution by species of mid- and overstory trees (≥9
cm DBH), including a selection of off-plot individuals, in the POWCNA.
Diameter at breast height (cm) Standard large DBH
Common name Minimum Maximum Average deviation trees (cm)
Loblolly Pine 12.7 97.5 45.3 18.03 104.1
Sweetgum 9.4 61.0 17.7 9.14 78.0
Red Maple 9.4 30.7 13.2 3.71 40.9
White Oak 9.4 56.9 16.8 8.47 111.8
Southern Red Oak 9.9 71.6 37.8 16.85 93.7
American Hornbeam 9.7 16.3 11.8 1.85 21.1
Flowering Dogwood 9.7 16.5 12.2 2.02 21.3
Winged Elm 9.4 22.6 12.9 3.05 48.3
Sassafras 9.7 23.6 13.9 3.79 29.7
Eastern Hophornbeam 9.7 16.0 12.0 1.87 24.1
Blackgum 9.7 32.5 16.0 6.33 55.6
Post Oak 12.7 61.2 33.8 10.48 70.4
Shortleaf Pine 30.0 68.6 51.6 10.07 72.4
Water Oak 9.4 44.2 21.8 10.44 93.5
Black Oak 9.4 33.8 18.2 7.87 -B
Mockernut Hickory 9.4 24.6 17.0 6.35 42.9
White Ash 9.4 36.8 18.8 9.57 -
Black Cherry 9.7 46.2 20.7 10.86 48.0
Willow Oak 13.0 38.1 21.0 11.62 70.4
Redbud 9.9 12.2 10.8 1.21 18.0
Red Mulberry 10.9 20.6 14.9 5.07 24.4
American Elm 10.9 22.9 16.9 8.49 -
Eastern Redcedar 9.9 9.9 9.9 -C 48.3
Serviceberry 10.2 10.2 10.2 - -
Chinkapin 17.8 17.8 17.8 - 24.1
Sweet-leaf 10.9 10.9 10.9 - 19.0
Off-plot only species
Cherrybark Oak 92.5
Green Ash (Fraxinus pennsylvanica Marsh.) 65.5
Witch-hazel (Hamamelis virginiana L.) 9.1
Bitternut Hickory (Carya cordiformis (Wang.) K. Koch) 69.1
Persimmon (Diospyros virginiana L.) 19.8
ADBH measurements for very large individuals found outside of the 23 established study plots,
but within the general boundaries of the POWCNA.
BNo larger tree observed than on study plots.
CStandard deviations are not applicable to species with only one measured tree in the entire study.
458 Southeastern Naturalist Vol. 8, No. 3
A considerable range in pine ages for a given size class is also apparent
(Fig. 4). At the greatest extreme, our sample found several pines between 30 and
35 cm in DBH that varied from about 40 rings to as many as 105 rings—over 60
years difference. Most of the pines of similar diameter were not as different
Figure 3. Aggregate size class distribution of the trees >9.0 cm DBH (a) in the
POWCNA. This distribution can be broken down by species into suppressed (b),
intermediate (c), co-dominant (d), and dominant (e) size classes (note the different
scales for b–e).
2009 D.C. Bragg and E. Heitzman 459
in age, but 2–3 decades of age range were not unusual (Fig. 4). Furthermore,
though the data suggest a positive linear trend between DBH and pine age, this
relationship becomes less reliable with increasingly large stems. In fact, the
largest known (104.1 cm DBH) Loblolly Pine on this site produced only 81
rings when cored at DBH—considerably younger than some pines that were
much smaller in diameter (Fig. 4). The presence of low, large branch stubs and a
broad spreading crown are good indicators (Marks and Gardescu 2001) that this
particular pine was probably open-grown for most of its early years.
Coarse woody debris
Of the approximately 213 pieces of CWD per hectare in the POWCNA, a
decided majority (91%) were classified as logs, with 4.5% of the pieces being
snags and 4.5% called stumps (Table 5). Combined, these pieces of CWD
averaged 28.9 m3/ha in volume. Logs were found on all sample plots, but not
every location had a snag or stump. Logs contributed just over 92% of the
CWD volume in this stand, followed by snags (4.1%) and stumps (3.8%).
On average, most (73.4% of the 213.2 pieces/ha) of the CWD was assigned
to decay class 2 (Table 5). Very little freshly dead (decay class 1;
3.8%) or long-dead (decay class 3; 22.8%) material was encountered. These
abundance patterns were also roughly mirrored with their corresponding
Figure 4. Age-class structure of the pine component of the POWCNA. Filled symbols
are from the plot-based random sample, while the open symbols are from supplemental
pines chosen to fill data gaps.
460 Southeastern Naturalist Vol. 8, No. 3
volumes: decay class 2 had the most (79.9% of the total volume), followed
by decay class 3 (15.9%) and decay class 1 (3.8%).
The dead wood was more equitably divided between functional groups
than either abundance or volume. There was slightly more pine CWD than
hardwood (54.1% versus 45.9%, respectively; Table 5). In terms of volume,
pines were somewhat more dominant, comprising 64.4% of the 28.9 m3/ha
of CWD measured in the POWCNA. This discrepancy is due to the larger
average size of pine CWD compared to hardwoods. For instance, the biggest
individual piece of CWD was a 4.4-m3 pine log (decay class 2) that was
22.2 m long. In terms of volume, this single pine log contributed just over
8% of all of the CWD sampled in this study. Given that an average piece
of CWD totaled only 0.14 m3, this particular piece was highly infl uential in
determining the volume statistics found in the data in Table 5.
The POWCNA shares some attributes with other mature pine-hardwood
stands in the UWGCP of southern Arkansas. One of these common features is
the shift away from a fire-dominated disturbance regime towards one dictated
by wind, ice, and insects. Though fires periodically still burn through the area,
their frequency has undoubtedly diminished during the last century. These
changes to disturbance regimes have produced a cascade of interrelated biological
legacies that shape the stands seen today (e.g., Brewer 2001).
Understory woody vegetation patterns
Unlike many managed mature pine stands of natural origin in the UWGCP,
the POWCNA understory is dominated by hardwood tree seedlings and saplings.
In intensively managed pine forests, decades of herbicide use have
typically produced a pine- and shrub-dominated understory. This pattern is
seen, for example, in the Good and Poor Forestry Farm Forties on the Crossett
Table 5. Stand-level coarse woody debris attributes by the type of coarse woody debris (CWD)
found in the POWCNA. V = volume, D = diameter, and L = length. SD = standard deviation.
Largest piece by
CWD Pieces (number per ha) Volumes (m3 per ha) V D L
type AverageA SD Range AverageA SD Range (m3) (m) (m)
Log 193.8 91.4 61.7–395.1 26.6 18.4 4.9–77.9 4.4 0.7 22.2
Snag 9.7 9.8 0.0–37.0 1.2 2.5 0.0–11.9 1.0 0.4 15.2
Stump 9.7 11.1 0.0–37.0 1.1 1.8 0.0–7.7 0.6 0.6 2.7
DC1B 8.1 11.5 0.0–37.0 1.1 2.6 0.0–11.9
DC2 156.7 74.2 49.4–296.3 23.1 16.5 6.0–77.9
DC3 48.3 33.3 0.0–111.1 4.6 4.6 0.0–20.2
Hardwood 97.7 62.9 0.0–222.2 10.2 9.1 0.0–35.6
Pine 115.4 108.4 0.0–370.4 18.6 18.9 0.0–72.2
Totals 213.2 28.9
ADue to rounding, totals of average values may not be exact between CWD types.
BDC1 = decay class 1; DC2 = decay class 2; DC3 = decay class 3. See text for definitions.
2009 D.C. Bragg and E. Heitzman 461
Experimental Forest, while the adjacent untreated RRNA has experienced a
decades-long dominance of a hardwood understory to the almost complete exclusion
of pines (Cain and Shelton 1995, 1996). Most of these hardwoods are
of greater shade tolerance than pines or early successional hardwood species,
further reinforcing the RRNA’s transition (barring severe catastrophic disturbance)
to closed-canopy hardwood forest.
Lianas are abundant in many managed and unmanaged forests of the
UWGCP (e.g., Blair and Brunett 1976), especially when not treated to limit
their competition with trees. Presumably, lianas have increased during the
decades since canopy closure in the unmanaged POWCNA. Unfortunately, we
lack longitudinal data on the dynamics of lianas in this particular stand. However,
this trend has been noted by Allen et al. (2007) in bottomland forests in
other parts of the southeastern United States. It is apparent when crossing the
POWCNA that the spreading crowns of woody vines occupy much of the midstory
canopy, and hence intercept a considerable portion of the light that otherwise
would have reached the understory. This, in turn, produces an increasingly
shaded environment for shade-intolerant tree species already struggling to
survive under a partial tree overstory. Whether the result of long-term fire suppression
(Bragg 2004b) or changing climatic conditions (Allen et al. 2007),
the increase in lianas in unmanaged southern forests and their interception of
a large portion of the light available has serious implications for the regeneration
of many different tree species, especially the shade-intolerant pines.
Overstory recruitment dynamics
At the POWCNA, early tree establishment was primarily pine. Following
canopy closure, tree regeneration shifted to increasingly shade-tolerant
hardwoods including Quercus, Carya, Acer, Cornus, Ulmus, Nyssa, and Ostrya.
Only a few small pine seedlings can be found in the present-day stand
(Table 1). This shift in recruitment is certainly not due to a dearth of pine
propagules but rather a function of shading, the long-term absence of surface
fires, and the lack of suitable pine seed germination conditions (Blair and Brunett
1976, Schultz 1997).
Unlike some studies that have repeated measures of species composition
to show the long-term trends of mature pine-dominated forests in the Gulf
Coastal Plain (e.g., Blair and Brunett 1976, Bragg 2006, Fail 1991, Shelton
and Cain 1999, Switzer et al. 1979), our interpretation of the future trajectory
of the POWCNA is based solely on the current picture of the stand. However,
barring a catastrophic disturbance severe enough to open the stand and provide
favorable germination sites, the Loblolly and Shortleaf Pine-dominated
overstory will inevitably die, and the lack of advanced pine regeneration implies
that only hardwoods will remain to exploit the gaps formed (Quarterman
and Keever 1962; Schultz 1997, 1999). Halls and Homesley (1966) came to
the same conclusion in a second-growth, unmanaged, pine-hardwood stand in
southeastern Texas, even though this stand had experienced surface fires often
during its first 50 years; 25 years of fire suppression resulted in hardwood occupation
and dominance of the lower crown levels.
462 Southeastern Naturalist Vol. 8, No. 3
Over time, researchers have gradually learned more about the role of natural
disturbances in healthy forest ecosystems (e.g., Crow 1978, Glitzenstein
et al. 1986, Oosting 1944). For example, barring stand-replacing disturbances
such as fire, Switzer et al. (1979) noted that comparable unmanaged pinehardwood
stands transition into hardwood-dominated forests at 100–130
years after old-field abandonment. This change, though dramatic, was not
abrupt—they defined a middle successional stage in which pine composition
declined from 80% of total stand basal area to 65% between years 45
and 100. Pine dominance continued to fall during the next 150 years, until
it comprised <10% of the density at 250 years (Switzer et al. 1979). In the
POWCNA, pine constituted just under 64% of the basal area (Table 3), suggesting
that the stand most closely resembles a 100-year-old pine forest just
beginning its transition to hardwood dominance—even though most of the
pines are between 60 and 85 years old.
Unmanaged multi-aged pine stands (such as the POWCNA) are likely
to transition differently than the even-aged stands assumed in the original
Switzer et al. (1979) study. Both the RRNA on the Crossett Experimental
Forest (Shelton and Cain 1999) and the Levi Wilcoxon Demonstration Forest
(Bragg 2004b) had higher pine basal areas (61% and 57%, respectively) than
expected for their pine overstory ages (between 70 and 140 years and 100 to
300 years, respectively). Some of these discrepancies probably arose from
differences in the management and environmental history of these stands,
while others are associated with the dilution of cohort-based mortality in
older, uneven-aged stands of pine prior to the suppression of fire and extensive
invasion by hardwoods. Regardless of age structure, most unmanaged
older pine-dominated forests are rapidly losing their pine overstory without
replacement (Bragg 2006). Attempts to restore fire to these locations to suppress
hardwoods and promote pine regeneration have been complicated by
the establishment of persistent hardwood rootstocks capable of resprouting
after top-killing fires (Garren 1943, Hodgkins 1958, Reynolds 1956).
Pine age distribution
Data from the POWCNA indicates that the pine component of the
overstory recruited to the canopy over multiple decades. This distribution
(Fig. 4) indicates that this particular second-growth pine-dominated stand
is uneven-aged and implies gradual canopy closure, rather than a pulse of
recruitment following a specific disturbance. In contrast, Turner (1937)
provided examples of second-growth Loblolly and/or Shortleaf Pine stands
in southern Arkansas with much narrower ranges of pine ages (80–95 years,
78–91 years, 109–116 years, and 104–119 years). Their relatively pure,
pine-dominated species composition, coupled with narrow age ranges,
was thought to result from old-field recolonization or recovery following a
catastrophic natural disturbance, specifically severe winds (Turner 1937).
Bragg (2004a) also described a 1930s-era second-growth pine-dominated
Loblolly stand in Ashley County, AR, as even-aged. This age structure was
inferred from some unpublished correspondence cited in Bragg (2004a) of
2009 D.C. Bragg and E. Heitzman 463
a different old-field stand of Loblolly Pine witnessed by Ike Rawls, former
superintendent of the Crossett Experimental Forest. In his letter, Rawls reported
a visit with Professor H.H. Chapman of Yale University and remarked
that these old-field pines were about 76 years old, and ≤71 cm in DBH (with
an average of 51 cm DBH), not including smaller suppressed pines. It was
logical, Bragg (2004a) concluded, that the 1930s-era stand was similarly
aged—other examples of dated and similarly structured stands can be found
in the literature (e.g., Glitzenstein et al. 1986).
The results of the POWCNA study offer a different possibility—the pines
in the 1930s-era stand may actually have much more variation in age than
first thought. Both stands display a range of pine size classes, though the largest
pines (and hardwoods) in the POWCNA are noticeably bigger (Table 4)
than those in the 1930s-era stand (Table 2 in Bragg [2004a]). Otherwise, both
stands exhibit a comparable, broadly unimodal pattern, with Loblolly primarily
occupying the larger classes (Fig. 3, and Fig. 3 in Bragg [2004a]) and
smaller hardwoods dominating the smallest classes. Regrettably, there is no
way to document the actual age structure of the 1930s-era stand, as these data
were not collected in the original sampling (Bragg 2004a). Conventional wisdom
has often labeled the mature, second-growth pine forests of the region as
even-aged, and the variation in pine size resulting from differences attributable
to local site conditions, competition/suppression, or genetic variation.
Undoubtedly, these factors have come into play, as the extensive logging,
land clearing, and agricultural abandonment of the UWGCP has produced
myriads of even-aged, second-growth pine stands. However, it is also obvious
that exceptions to this overstory recruitment pattern can be found—stand
history can be considerably more complicated than presently assumed.
As an example, the logging that started in the late 19th century and continues
to the present has not completely eliminated old pines in the UWGCP,
even though it greatly diminished their abundance across the landscape.
Rather, early logging operations typically “high-graded” standing timber,
with the choicest and most merchantable trees and species removed and the
remainder left behind (e.g., Hall 1945, Reynolds 1980). Hence, in addition
to the gradual recruitment and occupation of cleared former agricultural
lands, the inefficiency of this lumbering often produced stands with scattered
large cull stems, now-released intermediate and suppressed stems, and
an abundance of new seedlings. Over time, these stands often developed
into what was sometimes thought of as even-aged second-growth, even
though they may be better identified as multi-aged stands with scattered oldgrowth
individuals. The RRNA, as an example, was cut prior to 1920 using
a diameter-limit cut, with pines >38 cm or larger at the stump felled and all
other “submerchantable” stems left (Cain and Shelton 1994). Thus, given the
eventual protection of this stand in the RRNA, a few trees 130–150 years
old can still be found (Cain and Shelton 1994). Hence, it was not surprising
to find an isolated individual on the POWCNA that appears to be ≥120 years
old—it would have been too small and isolated when major logging occurred
464 Southeastern Naturalist Vol. 8, No. 3
to have been cut at that time, and decades of protection have allowed it to
emerge over a stand of younger hardwoods.
Historical and ecological legacies
Very little obvious evidence of the historical logging or agricultural practices
remains. Only a handful of stumps with signs of cutting still survive,
and these are well-decayed and weathered, indicating that they are decades
old (these are not remnants of the virgin forest, but rather pines felled in the
mid-20th century). In fact, most of what remains of this particular legacy
is the resin-soaked pine heartwood. No specific evidence (e.g., furrows)
of historical row cropping is apparent, although a handful of old trails or
roads are visible, especially where they eroded some of the steeper slopes
on the site. There may also be indications of an old fire break along a portion
of the stand, although there is no way to confirm this feature. A handful of
old stumps have some charring from past fires, but there is no fire scarring
(“catfaces”) on any of the standing timber, indicating that if fire had occurred
in the forest following agricultural abandonment, it was either too low in
intensity to damage the trees, or it happened long enough ago to have been
completely encapsulated by the trees.
Beyond available written records, the best biological evidence of the
open-grown origins of this stand can be found in the morphology of some
of the trees scattered throughout the stand. Marks and Gardescu (2001) provided
a blueprint for the examination of modern stands for historical land use.
Features such as well-defined edges in the age-and size-class structure of the
overstory, remnant species of old-field conditions, “wolfy” tree forms, and
other evidence of the presence or absence of human activities (e.g., the lack of
tip-up mounds in plowed fields) are example indicators of past treatments. The
POWCNA displays several of these characteristics. The largest Loblolly Pine
found in the entire stand, for example, still shows the remnants of branches
within 3 m of the ground and many large, stout branches in its crown, indicating
that this tree grew most of its early life under open conditions. A high rate
of Phellinus pini Ames (Red Heart) infection is also suggestive of old-field
stand development. Pines that grow in more open conditions tend to develop
larger, more persistent branches, which better serve as avenues for heart rot
fungi to enter than branches that form under closed canopy conditions (Hepting
and Chapman 1938). Similar wolfy branch patterns and widely spreading
crowns are also evident with the biggest oaks found on the site.
While past farming practices are known to produce long-term impacts
on forest recovery (e.g., Flinn and Vellend 2005, Hedman et al. 2000), given
the estimated 80–100 years of relatively undisturbed reforestation that has
occurred in the POWCNA, little remains to suggest agriculturally based
human infl uences. Because most of the upland agricultural efforts in southern
Arkansas were abandoned before they depleted the land in the late 19th
and early 20th centuries, site conditions have not been drastically changed
in most locations. After about 60 years, Switzer et al. (1979) reported that
most soil properties, including litter composition and depth, organic matter
2009 D.C. Bragg and E. Heitzman 465
content, and soil chemistry, had largely recovered to “undisturbed” levels in
a chronosequence of pine-hardwood forests in eastern Mississippi. If historical
disturbance regimes had also been imposed on the POWCNA following
agricultural abandonment, at least the stand overstory may have also returned
to what may have been expected in a comparably aged pine-hardwood
virgin forest. However, continued fire protection, coupled with the presence
of invasive species, will ensure that some departure from presettlement forest
structure, composition, and function will persist.
One such biotic legacy can be seen in the tree composition of the POWCNA.
Eastern Redcedar, for instance, was not used as a witness tree in the
General Land Office (GLO) public land survey notes from Ashley County,
AR, just south of the study area (Bragg 2003) or near Warren, AR, just to the
west (D.C. Bragg, unpubl. data). Although not abundant in the POWCNA,
Eastern Redcedar is present in places on the natural area. Most of these individuals
are fairly large, with many dead low branches, and probably are 70
or more years old (the only Eastern Redcedar cored had at least 70 obvious
annual rings). In this part of Arkansas, our personal experience has found
that Eastern Redcedar is comparatively uncommon and usually associated
with old homesites, fields, pastures, and fencerows. Indeed, a number of
dead and fallen large Eastern Redcedars were found surrounding the historic
homesite on the POWCNA.
Coarse woody debris
Dead trees have long been recognized as important substrates for southern
forests (e.g., Lemon 1945, McMinn and Crossley 1996). A history of
agricultural use, followed by reforestation, has been shown to depress CWD
for decades (e.g., Lõhmus and Lõhmus 2005). CWD is not a prominent
part of the current biophysical structure of the POWCNA, even though it is
accumulating in some portions of the stand. Much of the CWD is in smallsized
pieces, often of easily decayed hardwoods, and hence has a fairly short
residency. Large pine logs, snags, and stumps are usually the most persistent
pool of CWD in stands such as the POWCNA. Given that few truly decay-resistant
species are found in these stands, most dead wood disappears quickly
in the warm, humid, termite-filled environment of southern Arkansas. This is
true for the dead pine—their long-term persistence is more a matter of sheer
size and their tendency to develop a core of resin-soaked, decay-resistant
heartwood (also called “rich pine”). Unless consumed by fire, these resinous
cores can last for decades, even when in contact with moist ground.
Only a few of the overstory pines have recently died. However, because
of the relatively short lifespan of Loblolly and Shortleaf on mesic sites in
this region, pine mortality is expected to increase significantly over the next
few decades. Observations on dead-wood abundance and volume show
that the POWCNA has roughly the same volume of CWD as a comparably
aged, managed Loblolly-Shortleaf Pine stand on the Crossett Experimental
Forest and dramatically less than 2 older, unmanaged pine-hardwood
stands (Table 6). However, the POWCNA is rapidly approaching a stage in
466 Southeastern Naturalist Vol. 8, No. 3
its developmental history likely to be marked by significant pine mortality,
with each dead pine contributing a large quantity of CWD. The dense stand
that has developed over the last century has slowed the growth of the pine
overstory appreciably. The emergent pines are more susceptible to events
such as lightning strikes or wind gusts that may kill or injure them. Wounded
pines can serve as the focal point for insects, including bark beetles such as
Dendroctonus and/or Ips spp., and this can lead to larger outbreaks. Cain and
Shelton (1996) reported such a sequence of events in the RRNA that quickly
killed about 10% of the pine overstory. Severe windstorms have also disproportionately
affected exposed pine timber in other mature pine remnants near
the POWCNA (e.g., Bragg 2006). These exogenous factors will progressively
reduce the pine dominance to a fraction of its past total, and almost all pines
will die before they reach 300 years of age (Switzer et al. 1979).
The relatively small stature of most hardwoods in the POWCNA limits
their contribution to the stand CWD totals—on average, their volumes
are appreciably less than the much larger overstory pines. However, for a
stand of the age of the POWCNA, this is probably not the only reason why
hardwood CWD totals are limited. Spetich et al. (1999) found that 50 - to
120-year-old hardwood-dominated forests tend to have lower CWD volumes
than either younger or older stands. Hardwood stands of intermediate age
typically have less CWD largely because they lack the dead wood legacies
from the previous stand and decay-prone hardwood snags are also shortlived
across most of the region. Cain (1996) noted that hardwood snags had
changed from 56.3% “hard” (i.e., relatively sound) and 43.7% “soft” (i.e.,
decayed) 2 years after being injected with herbicides to 8.7% hard and 91.3%
soft by 6 years after treatment.
The POWCNA’s prominence of pine (and to a lesser extent, certain
shade-intolerant species of hardwood) is consistent with the dominant
Table 6. Coarse woody debris abundance and volume in some mature pine-hardwood stands of
Arkansas Count Volume
Stand county Management regime (#/ha) (m3/ha) Source
POWCNA Drew Unmanaged second-growth 213.2 28.9 This study
Good FortyA Ashley Managed second-growth -B 35.5 Zhang (2000)
Reynolds RNAA Ashley Unmanaged second-growth -B 93.7–309.7 Zhang (2000)
(with some old-growth culls)
Levi Wilcoxon Ashley Old-growth 33.0 191.0 Bragg (2004b)
DFC (some salvage of dead pine)
AThe Good Forty and Reynolds Research Natural Area are found on the Crossett Experimental
Forest of the USDA Forest Service.
BNo count data for all types of CWD.
CThe Levi Wilcoxon Demonstration Forest is owned by Plum Creek Lumber Company.
2009 D.C. Bragg and E. Heitzman 467
vegetation patterns this particular site would have had prior to Euroamerican
settlement of the region. The multiple age classes currently found
in the pine component also probably reflect the often complex nature of
stand origin in this region, with numerous cohorts periodically recruited
as the landscape responded to geological and edaphic controls, natural
disturbances, and human influences (Bragg 2006, Peacock et al. 2008).
However, the recovery of the arboreal component of forests is but
one of many indicators of ecological restoration following agricultural
abandonment and reforestation. This study considered only the woody
plant components of the POWCNA—forest herbs, non-vascular taxa,
fauna, fungi, etc. were not studied. These components can take decades
longer to recover pre-disturbance levels, especially if propagule dispersal
limitations are present (Flinn and Vellend 2005). The presence of invasive
woody species such as Ligustrum sinenese Lour. (Chinese Privet) and
Lonicera japonica Thunb. (Japanese Honeysuckle) in the area, coupled
with the absence of regular surface fires, decades of native hardwood expansion,
and alterations to historic disturbance regimes further complicate
the return of historical forest cover. Hence, additional study is needed to
examine the full suite of environmental conditions presented in the POWCNA
to determine if this stand should be considered a viable example of
mature southern pine-dominated forest, or if it still suffers from a legacy
of past land-use practices.
Over 60 years ago, H.H. Chapman advocated for natural-area establishment
to be driven by more than just the desire to protect unique
environmental attributes. Rather, he envisioned a wide range of stand
conditions being protected from human intervention but still under the
full influence of natural disturbance regimes, even if they occasionally
obliterate the original feature for which the stand was preserved (Chapman
1947). In doing so, the full range of ecosystem functionality would
be preserved. Decades of practice, however, have proved antithetical to
this vision, as resource managers have diligently worked to keep certain
natural disturbances (e.g., fire) from protected remnants, or to minimize
the impacts of other events (e.g., insect outbreaks, ice or wind storms)
through salvage harvests. The fact that most natural areas are small and
imbedded within intensively manipulated landscapes has not helped, as
liability issues pressure managers to stem events propagating from their
properties. Perhaps the best conservation value of this protected parcel
is that the POWCNA represents a rapidly vanishing example of a mesic,
mature, unmanaged pine-hardwood forest on the UWGCP in southern
Arkansas. Given the South-wide conversion of structurally and compositionally
diverse natural-origin pine-dominated forests to pine plantation
monocultures, agricultural lands, and commercial/residential areas (Conner
and Hartsell 2002), this loss may become a key conservation issue in
the 21st century.
468 Southeastern Naturalist Vol. 8, No. 3
We thank the following for their contributions to this project: Brad Sears, Kirby
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