The Big Thicket
2009 Southeastern Naturalist 8(Special Issue 2):1–30
An Ecological Classification System for the National
Forests and Adjacent Areas of the West Gulf Coastal Plain
James E. Van Kley1,* and Rick L. Turner1
Abstract - We developed a multifactor ecological classification system (ECS) for
the National Forests and adjacent lands of Texas and Louisiana. The ECS classifies
lands into ecosystem types: repeating combinations of potential natural vegetation,
soils, and physiography. This paper uses results of a portion of this effort from the
northern part of Louisiana’s Kisatchie National Forest as an example. Forest stands
were sampled across a range of soil and topographic situations. Non-metric multidimensional
scaling ordinations and TWINSPAN classification of the samples based on
ground-layer vegetation corresponded to gradients of topographic position, fire frequency,
disturbance, and soil nutrients. A separate ordination of only upland stands
clarified relationships between upland vegetation and soil texture. Ordination and
TWINSPAN results formed the basis for a final classification of the sample stands
and for descriptions and dichotomous keys for seven “land-type phases”—local ecosystem
types that share soil and topographic attributes, natural plant communities,
and responses to management or disturbance. ECS provides an ecologically relevant
way to stratify the landscape for inventory, conservation, research, or management
and gives the Forest Service and other professionals a valuable tool to aid in making
ecologically informed decisions. Future goals include mapping ecological units on
National Forest lands and expansion of the area covered.
Introduction
Most land classifications focus on only one aspect of the land resource such
as ownership or political boundaries, existing vegetation types, topography, or
soils. Classifications based on soils are widely used in forest inventory, but if
their relationship to the biota is unknown, they are not fully relevant to forest
management. Transitory phenomena such as existing plant communities or
forest cover types form the basis for other classifications; these can become obsolete
due to logging, storms, other disturbances, or natural succession.
An ecological classification system (ECS) provides an alternative approach.
An ECS expresses in simplified terms the interrelationships between
vegetation and other parts of an ecosystem such as physiography (landform and
topography) and soils and uses repeating combinations of these multiple ecosystem
components to classify land. Physiography infl uences microclimate,
drainage, and solar radiation, and correlates with soil conditions. Soil texture,
nutrients, and moisture-holding capacity affect plant species composition and
productivity, while the vegetation on a site serves as a “phytometer” that integrates
environmental factors and gives them ecological meaning (Barnes et
1Department of Biology, PO Box 13003, Stephen F. Austin State University, Nacogdoches,
TX 75963. *Corresponding author - jvankley@sfasu.edu.
2 Southeastern Naturalist Vol. 8, Special Issue 2
al. 1982). The product of an ECS is a manual containing descriptions of “ecological
units” consisting of predictable combinations of soils, potential natural
vegetation, and physiography. Ecological units are based on long-lived ecosystem
attributes (soil properties, topography, and potential vegetation), but at
the same time are relevant to existing vegetation patterns and thus highly relevant
to conservation or management. Descriptions of ecological units can be
used to identify the “ecological type” of any site in the covered region prior to
management, conservation activities, or research. ECS can also be used to generate
maps showing the distribution of ecological units across the landscape.
An ECS-based map does not become obsolete when vegetation changes—in
fact, several vegetative communities may be possible on one ecological type
depending on management or successional stage. This paper describes an ECS
for the national forest lands and adjacent areas of the Texas and Louisiana West
Gulf Coastal Plain, focusing on data collected in northern Louisiana to illustrate
the ECS development process.
Multiple-factor ecological classification systems
The earliest multiple-factor ECS, initiated by G.A. Kraus in the German
state of Baden-Württemberg, has been in use since about 1946 (Spurr and
Barnes 1980). In the US, Barnes et al. (1982) developed an ECS based on the
Baden-Württemberg model for the Cyrus McCormick Experimental Forest
in Michigan. Other examples are from the Piedmont and Upper Coastal Plain
provinces in South Carolina Jones (1991), Michigan’s Sylvania Recreation
Area (Spies and Barnes 1985), the Savannah River Plant in South Carolina
(Van Lear and Jones 1987), the Shawnee Hills in Illinois (Fralish 1988), the
Kickapoo River watershed in southwestern Wisconsin (Hix 1988), Huron
and Manistee National Forests in Michigan (Cleland et al. 1994), Hoosier
National Forest in Indiana (Van Kley and Parker 1993), Wayne National Forest
in Ohio (Hix and Pearcy 1997), and Hiawatha National Forest in Michigan
(Kudray 2002). In the western US, a related approach based largely on
old-growth vegetation (which is assumed to “integrate” multiple ecosystem
components), known as “habitat typing,” has long been in use on National
Forest lands (e.g., Daubenmire 1980, Daubenmire and Daubenmire 1968).
The initial ECS field guide for the Texas and Louisiana West Gulf Coastal
Plain was submitted as an unpublished report to the US Forest Service by
Turner et al. (1999) and revised and expanded into a 379-page, color-illustrated
“Second Approximation” (Van Kley et al. 2007) in 2007.
Vegetation studies on the West Gulf Coastal Plain
Numerous previous studies provided background for ECS including
descriptions of individual local plant communities (e.g., MacRoberts and
MacRoberts 1992, 1995, 2004; Marietta and Nixon 1983; Nixon et al. 1980).
Several papers also describe landscape-wide vegetation-environment relationships
from the Big Thicket area of southeast Texas (immediately south of
the ECS study area), the most notable being Marks and Harcombe (1981) and
Harcombe et al. (1993). While such literature formed a good working first
2009 J.E. Van Kley and R.L. Turner 3
approximation for ecological classification, we desired that ECS be based
primarily on independent quantitative data so that the previous studies could
be used to corroborate ECS results. Several theses and publications provide
detailed analyses and summaries of portions of the ECS data (collected in
stages over a period of more than 10 years) including Dehnisch (1998), Mundorf
(1998), Van Kley and Hine (1998), Turner, (1999), Van Kley (1999a),
Van Kley (1999b), and Quine (2000); a generalized version of the resulting
ecological units is presented by Van Kley in Diggs et al. (2006).
Objectives
Relating patterns of natural vegetation to natural environmental factors
is the core of ecological classification; of many possible soil and
physiographic factors, we desired to find ones strongly related to natural
vegetation. Once these factors were identified, ecological types could be
described. The aim of our study was to use field data to identify vegetation-
environment relationships and use these relationships to develop the
local-level (land-type and land-type phase) ecological units for the national
forests and adjacent areas of the West Gulf coastal plain. To accomplish
this goal, we sampled sites from a range of geological, topographic, and
soil settings covering much of the region and subjected the resulting vegetation
and environmental data to multivariate analysis. In this paper, we use
previously unpublished data collected in 2002 from a portion of Kisatchie
National Forest in northern Louisiana as an example.
National hierarchy of ecological units
The local ECS is nested within a pre-existing National Hierarchical
Framework of Ecological Units (Table 1): a scientifically derived regionalization
of ecosystems organized into nested, increasingly homogeneous
units of decreasing orders of scale from upper to lower levels (McNab and
Avers 1994). Our ECS inherits this hierarchy and extends it by developing
local-level ecological units. At the highest level, Texas and Louisiana lie
entirely within the Humid Temperate Domain and the Subtropical Division
(Bailey et al. 1994). Ecosystem units at a regional scale (“province,” “section,”
and “subsection”), are based on combinations of regional climate,
geology, and broad-scale vegetation types. Bailey et al. (1994) and McNab
and Avers (1994) described the domains, divisions, provinces, and sections
for the US, while Keys et al. (1995) mapped the eastern and southern US
sections and subsections. The greater study area (Fig. 1a) occurs across three
provinces and three sections: the Middle Coastal Plain, Western Section
(231E); the Coastal Plains and Flatwoods, Western Gulf Section (232F); and
the Mississippi Alluvial Basin Section (234A). We collectively refer to these
as the West Gulf coastal plain.
Local-level ecological units, based on local patterns of natural vegetation,
soils, geology, and topography are in decreasing order of scale, the
“land-type association” (LTA), “land-type'” (LT), and “land-type phase”
(LTP). The US Forest service previously delineated 18 LTAs across the
4 Southeastern Naturalist Vol. 8, Special Issue 2
national forest lands of Texas and Louisiana largely on the basis of geology
and broad vegetation differences mainly related to the former natural range
of upland Pinus palustris P. Mill (Longleaf Pine) communities (USDA Forest
Service 1996, 1997). Circumscription (though not mapping) of land-type
Table 1. Hierarchical levels of the USDA Forest Service Ecological Classification and Inventory.
Modified from Forest Service Handbook 1909.21 (USDA 1979).
Planning
Level Factors Approximate scale level
Province Geomorphology, climate Multi-state Nationalregional
Section Geomorphology, climate, 1000’s of square miles Regionalvegetation
subregional
Subsection Climate, geomorphology, 0 to 100s of square Multi-forest,
vegetation miles state
Landtype Landforms, natural overstory 10s to 10,000s of acres Forest
association (LTA) communities, soil associations
Landtype (LT) Landform, natural 10s to 100s of acres Ranger
vegetative communities, soils district,
Management
area,
Opportunity
area
Landtype Soils, landscape position, 1 to 100s of acres Project
phase (LTP) natural vegetative
communities
Figure 1 (opposite page). Study area. a) Locations of National Forest boundaries (dark
outlines) and the provinces, sections, and subsections of the national ECS hierarchical
framework on the West Gulf Coastal Plain of Texas and Louisiana. The subsections
with the majority of National Forest lands are: for the Southeastern Mixed Forest
province (231)—231Ea (South Central Arkansas), 231Ef (Piney Woods Transition),
231Eg (Sand Hills), and 231Eh, (Southern Loam Hills); for the Outer Coastal Plain
Mixed Forest Province (232)—232Fa (Southern Loam Hills) and 232Fe (Piney
Woods Transition). 232Fc and 232Fd are alluvial valley subsections associated with
major rivers. 234Ai is the Red River Alluvial Plain subsection of Louisiana. Eighteen
land-type associations (LTAs) occur in the portions of the subsections with USFS
lands. SHNF, DNF, ANF, and SNF = Sam Houston, Davey Crockett, Angelina, and
Sabine National Forests, respectively. The map is modified from Keys et al. (1995).
b) Location of the Caney Ranger District of Kisatchie National Forest (dark outlines)
within the South Central Arkansas subsection (231Ea) and North Louisiana Clayey
Hills (231Ea.9) LTA. Adjacent LTAs include 231Ea.8 (Caney Lakes Rolling Uplands),
231Ea.4 (Alluvial Floodplains and Terraces), and 234Ai.7 (Red River Alluvial
Plain). Numerals in the 3 Caney Ranger District units represent the number of stands
sampled from (left to right) the Caney, Middlefork, and Corney Units.
2009 J.E. Van Kley and R.L. Turner 5
phases and the land-types within which they are nested was the aim of our
study. This paper describes development of land-type phases for a land-type
association known as the “North Louisiana Clayey Hills,” or “231Ea.9,”
which is in the South Central Arkansas Subsection (231Ea) and contains
most of Kisatchie National Forest's Caney Ranger District (Fig. 1b).
Methods
Study area
The general study area included the lands of Louisiana's Kisatchie National
Forest and the four national forests in Texas (Fig. 1a). Louisiana and
6 Southeastern Naturalist Vol. 8, Special Issue 2
eastern Texas have a humid, subtropical climate with hot, humid summers,
mild winters, occasional frost, and negligible snowfall (Larkin and Bomar
1983). Precipitation occurs year-round, but more falls in winter and spring.
Summer precipitation is usually from afternoon thunderstorms, lightning
from which ignited low-intensity fires that frequently burned through the
pine-dominated woodlands typical of the region's presettlement uplands
(Christenson 1981, Frost 1993). Mean annual precipitation increases from
west to east, ranging from 42 inches (107cm) in Houston County, TX (Larkin
and Bomar 1983) to 57 inches (145 cm) in Rapides Parish, LA (Kerr et al.
1980). Surface geology consists of a series of largely east–west sedimentary
deposits that become progressively younger from north (Eocene) to south
(Miocene and Pliocene) (Bureau of Economic Geology 1975, 1979, 1993;
Sellards et al. 1932; Snead and McCulloh 1984).
The North Louisiana Clayey Hills LTA is a rolling terrain on Eocene-aged
Cook Mountain and Cockfield surface geology (USDA Forest Service 1997)
that encompasses most of the Caney Ranger District of Kisatchie National
Forest (Fig. 1b; Snead and McCulloh 1984). Presettlement upland vegetation
consisted of Shortleaf Pine-oak-hickory communities (Mohr 1896, Sargent
1884), although presently most stands are second-growth Pinus taeda L.
(Loblolly Pine)-Liquidambar styracifl ua L. (Sweetgum)-oak forests. The area
is outside of the natural range of Longleaf Pine communities (Frost 1993).
Field sampling
The overall ECS strategy involved sampling a series of stands in each
of the previously defined 18 LTAs on national forest lands, thereby compiling
a series of essentially independent data sets each covering one to
several adjacent LTAs. Here we describe sampling on Kisatchie National
Forest's Caney Ranger District; methodology for the remaining datasets
was similar and is described in Dehnisch (1998), Mundorf (1998), Turner,
(1999), Van Kley and Hine (1998), Van Kley (1999a), Van Kley (1999b),
and Quine (2000).
Desiring to reduce the infl uence of historical factors on plant communities
so as to not obscure relationships with soil and physiography, we only
used stands listed in the Forest Service’s Continuous Inventory of Stand
Conditions (CISC) database as being more than 60 years of age. To ensure
data represented the region's full ecological range, we generated a list of
age-eligible stands from each forest compartment in the District and used
USGS topographic maps and soil maps (Kilpatrick and Henry 1989, Kilpatrick
et al. 1998) to sort stands into “selection types” based on topographic
position and soils (Table 2). Random stands from each selection type were
field checked and approved for sampling if free from substantial recent disturbance
or excessive heterogeneity. “Unusual” sites (three forested seeps
and a fl oodplain depression with Taxodium distichum (L.) L.C. Rich. [Bald
Cypress]) were also selected if they met age and disturbance criteria.
In each stand, we established a transect from a random starting point and
located four points at 20-m intervals along the transect. Each point defined
2009 J.E. Van Kley and R.L. Turner 7
a plot with a series of nested subplots: A 1000-m2 “search area” a 250-m2
circular subplot, a 100-m2 subplot, a 10-m2 subplot, and a 1-m2 subplot. The
presence of ground-layer species (<1 m tall) in this series of subplots with
increasing area was scored: plants occurring in the 1-m2 subplot were given
an occurrence rank of 5, those not in the 1-m2 subplot but growing in the
10 -m2 subplot were given a rank of 4, those only in the 100-m2 subplot were
given a rank of 3, and those only within the 1000-m2 area were given a rank
of 2 if there were three or more individuals or colonies and a rank of 1 if
there were only one or two individuals or small colonies. The 1000-m2 search
area, its long axis perpendicular to the transect, extended 25 m on each side
of the transect and 10 m along the transect on each side of the plot center
point. Boundaries, located by pacing and marked with fl ags, were approximate,
but care was taken to insure no overlap with adjacent plots. A mean
occurrence rank was calculated for each species over the four plots in each
stand. This abundance measure was used in subsequent analyses because
multiple data were collected by multiple persons over several years and the
occurrence ranks were deemed more objective and uniform across datasets
than coverage estimates. Stems were counted for woody species less than 10
cm dbh occurring in the 100-m2 subplot; understory trees and shrubs were
not used in the analyses, but they contributed to LTP descriptions in the ECS
field guide. Diameters (dbh) were recorded for all stems greater than 10 cm
dbh. in the 250-m2 subplot. Taxonomy followed Kartesz (1999).
The texture, color, and depth of each soil horizon was described from a
soil pit located in a random direction roughly 3 m from the center point of the
2nd plot and three, likewise-located auger cores at plots 1, 3, and 4. A topsoil
sample from a depth of 10–15 cm was analyzed for texture (percentage clay,
sand, and silt) and soil properties including pH, nitrates (mg/L), phosphorus
(mg/L), potassium (mg/L), calcium (mg/L), magnesium (mg/L), zinc (mg/L),
sulphur (mg/L), manganese (mg/L), copper (mg/L), and iron (mg/L) at the
Stephen F. Austin State University Soil Testing Laboratory. Texture was also
estimated by feel at depths of 50 and 100 cm, and depth to gray redox depletions
was measured if observed within the top 150 cm.
Table 2. A list of the preliminary “selection types” used to stratify the landscape of the North
Louisiana Clayey Hills for sample selection. Soil textures refer to the finest texture within the
upper 50 cm of the profile. Even distribution of samples was impossible because of the rarity of
age/disturbance-eligible examples of certain types.
Selection type Number of samples selected
Sandy upper slopes and summits 0
Loamy upper slopes and summits 7
Clayey upper slopes and summits 11
Sandy lower slopes 2
Loamy lower slopes 4
Clayey lower slopes 5
Minor stream bottoms (<100 m wide) 7
Major stream bottoms (>100 m wide) 10
Other: seeps and swamps 4
8 Southeastern Naturalist Vol. 8, Special Issue 2
Physiographic measurements included slope gradient (%) and elevation
(m above sea level). Elevation of a sample site relative to that of the nearest
ridgetop or broad summit and to the nearest bottom (stream of 2nd or greater
order) was determined from a USGS topographic map. Topographic position
was calculated as [(site elevation - bottom elevation) / (ridge elevation - bottom
elevation)] x 100. Thus, summits and stream fl oodplains would have a
position of 100% and 0%, respectively. Each stand was evaluated on a scale
of 1–10 for evidence of fire (1 = extensive charred logs, blackened bark, fire
scars—indicative of recent and frequent fire; 10 = no visible evidence of
fire). Stands were also graded on a 12-point qualitative scale (1 = high, 12
= poor) for “natural quality” based on visible evidences of past disturbance
such as old stumps, fence remnants, exotic species, etc. Stand locations were
recorded with a global positioning system (GPS).
Data analysis
Species data (mean occurrence rank for ground layer and importance values
based on whole-stand relative density and basal area for overstory) were
subjected to non-metric multidimensional scaling (NMS; Mcune and Medford
1999) and two-way indicator species analysis (TWINSPAN; Hill 1979b). Data
were not transformed, but species found in only one sample were omitted and
a Taxodium distichum (L.) L.C. Rich (Baldcypress) swamp site was omitted
from the ordinations after a preliminary run showed it to be an outlier. We used
PC-ORD (Mcune and Medford 1999), which incorporates strict convergence
criteria, and corrected rescaling algorithms into TWINSPAN, addressing the
instability and sample order-dependence (Oksanen and Minchin 1997) of earlier
versions. For TWINSPAN, pseudopsecies cut-levels of 0, 2, and 4, were
used; all other options were left at their default settings. Divisions were recognized
down to the level (3rd and 4th in our case) where sample groups no longer
occurred in largely distinct regions when superimposed on a corresponding
ordination diagram and only species with mean occurrence >1.8 in at least one
of these groups were displayed in the final tabulation. The Sørensen distance
measure was used for NMS, and optimal dimensionality for each NMS was
determined by plotting stress against the number of dimensions. “Autopilot”
mode in PC-ORD was used: the optimal solution (minimum stress) from 40
runs with real data was selected, and a Monte Carlo test based on 50 runs with
randomized data tested the hypothesis that the stress of the final solution was
lower than that encountered at random. Resulting ordination axes (samples
ordered by species composition) were interpreted as refl ecting underlying
environmental gradients. Ground-layer vegetation was emphasized because
of the direct relationship between overstory and many common disturbances
such as selective logging, planting, pests (e.g., Dendroctonus frontalis
Zimmermann [Southern Pine Beetle]), and wind damage. Compositional gradients
(expressed by NMS scores) were compared with soil and physiographic
factors as well as with overstory NMS scores using Pearson’s correlations. To
clarify relationships among samples from upland sites, the upland samples, a
subset of 20, were ordinated separately and the initial TWINSPAN-derived
classification of upland samples revised accordingly. The resulting interpreted
2009 J.E. Van Kley and R.L. Turner 9
sample ordinations and classification were the basis for describing the landtype
phases for the North Louisiana Clayey Hills.
The Caney data were combined with the other ECS data sets from the
West Gulf Coastal Plain and the combined samples (420 stands and 815
species) subjected to detrended correspondence analysis (DCA; Hill 1979a,
Hill and Gauch 1980) based on mean ground-layer occurrence rank, thereby
allowing us to observe plant communities from the North Louisiana Clayey
Hills in the context of those from other LTAs. All samples, including those
from the Caney, were active, and no data transformations were used, but 23
non-forested samples from glades and prairies, the 19 samples from the Red
River Alluvial Plain, and species occurring in only one sample were omitted.
Samples in each non-Caney data set had been previously classified into
communities, and these classifications were pooled and displayed on the
resulting ordination diagram.
Results
We found 340 vascular plant species on 50 sample stands from the Caney
Ranger District of Kisatchie National Forest. A two-dimensional NMS ordination
(Fig. 2) of 49 stands and 286 groundlayer species based on mean
ranked-occurrence values showed a gradient of communities from those of
well-drained upland sites to those of irregularly and seasonally fl ooded valleys
of medium-sized and large streams (Corney Bayou and the Middle Fork
of Bayou D’Arbonne). Final “stress” for NMS was 15.29, final instability =
0.0001, and Monte Carlo P = 0.032. The ordination corresponded to several
soil and environmental factors: sites with low first- and second-axis scores
had higher topographic positions, were more acid, lower in nutrients, and
showed more evidence of fire than those with high scores (Fig. 2, Table 3).
Ground-layer ordination axes also correlated with the first and third axes
of a 3-dimensional NMS of samples based on overstory importance values
(Table 3; final stress = 14.97, instability = 0.00011, Monte Carlo P = .019):
lowlands were typically dominated by deciduous eudicotyledons (hardwoods),
sites from the middle of the gradient supported mixtures of Loblolly
Pine and hardwoods, and the uplands were pine-dominated. “Joint plot” vectors
on Figure 2 indicate the direction and relative strength of correlations;
the minimum r2 for joint-plot correlations displayed in the figure was 0.23.
TWINSPAN of all 50 samples resulted in classification of the samples
into seven groups (the six superimposed on Figure 2 and the Bald Cypress
swamp omitted from the ordination). Groups ranged from uplands dominated
by Shortleaf Pine-oak-hickory communities to the fl oodplains and
swamps along large streams (Appendix 1). TWINSPAN also classified the
species into seven species groups (Appendix 1). These groups were variously
characteristic of upland sites, mesic lower slopes and small-stream bottoms,
larger fl oodplains, forested seeps, and wetlands; an additional group
of widespread species occurred across a range of habits (Appendix 1). The
species groups were important in developing the descriptions of ecological
10 Southeastern Naturalist Vol. 8, Special Issue 2
units and also contributed to the “master” ecological species groups listed
in Van Kley et al. (2007) that were formed by combining equivalent species
groups from ECS data sets for all 18 LTAs. Appendix 1 provides the names
of the “master” ecological species groups to which each of the Appendix 1
groups are closest.
The gradients recovered by the ordination were dominated by topography
and soil nutrients; correlations with soil sand and clay were weak (Table 3).
Figure 2. A two-dimensional NMS ordination of 49 samples and 286 species from
the Caney Ranger District of Kisatchie National Forest based on mean rankedoccurrence
values for ground layer species. Final stress = 15.29, Monte Carlo P =
0.032, final instability = 0.0001. Dotted lines and labels indicate a classification of the
samples based on TWINSPAN. “Joint plot” lines indicate the direction and relative
strength of correlations between ordination scores and external environmental factors
(minimum r2 for joint-plot display = 0.23). Correlations with individual ordination
axes are shown in Table 3. “Less fire” is expressed on a scale of 1–10: 1= strong
evidence of recent or frequent fire, 10 = no evidence of fire. “MoDpth” = depth of
soil to gray redox depletions, “clay” = percentage of clay-sized mineral particles in
the topsoil. “T_Pos%” = topographic position % = vertical position of site relative
to the nearest local summit and steam bottom. “-NQ”= “natural quality” expressed
on a scale of 1–12: higher values = more evidence of disturbance and lower quality.
“OvNms1” and “OvNms3” = the 1st and 3rd NMS ordination axes of the 49 samples
based on importance values for trees >10 cm dbh.
2009 J.E. Van Kley and R.L. Turner 11
Among uplands, analysis resolved a “main” upland type with a Shortleaf
Pine-oak-hickory-Euphorbia corollata L. (Flowering Spurge)-Galactia
(milkpea spp.)-Desmodium spp. (ticktrefoil) community, and a more denselyshaded
Loblolly Pine-Sweetgum-Parthenocissus spp. (creeper) community
that was transitional fl oristically (and possibly topographically) to the mesic
sites (Fig. 2, Appendix 1). However, other West Gulf Coastal Plain data sets
and literature indicated relationships between soil texture and vegetation,
especially on upland sites (Marks and Harcombe 1981; Van Kley 1999a,
1999b). When we further investigated this possibility—eliminating most of
the strong upland/lowland gradient that might obscure other patterns by running
a separate 3-dimensional NMS (final stress = 10.7, instability = 0.00001,
Monte Carlo P = 0.02) with a subset of 20 “upland” samples and 185 species
(all the “dry-mesic” sites of Fig. 2 and two “borderline” mesic sites)—the first
axis of this upland NMS was indeed related to soil texture; clayey sites generally
had low scores and sites with loamy soils high scores, and percentages of
sand and clay throughout the soil profile were significantly correlated with the
axis (Fig. 3, Table 4). The third axis was correlated with natural quality (sites
with low scores showed more evidence of human impact) as well as to fire and
elevation (Fig. 3); the second axis also varied with fire and elevation (Table 4).
The second and third axes together largely represent the dimension previously
observed among the uplands in Figure 2.
ECS integrates fl oristic variation with soil and physiography, not disturbance
and site-history. However, ordering of upland samples in the analysis
of Figure 2 as well as the 2nd/3rd axes of the upland-only NMS (Fig. 3)
Table 3. Correlations between soil and topographic factors and the axes of a two-dimensional
non-metric multidimensional scaling (NMS) ordination of 49 samples and 286 species from the
Caney Ranger District of Kisatchie National Forest based on density-dependant ranked occurrence
of ground layer species. “Fire” is expressed on a scale of 1–10 with 1 = strong evidence
of recent or frequent fire and 10 = no evidence of fire. “Depth to gray mottles” = depth of soil
to gray redox depletions. “Topographic position %” = vertical position of site relative to the
nearest local summit and steam bottom. The critical value for r is 0.28 for P < 0.05.
NMS Axis
1 2
Topographic position % -0.53 -0.78
Elevation (m) -0.41 -0.71
Depth to gray mottles -0.76 -0.63
Fire 0.57 0.74
pH -0.69 -0.48
Manganese 0.30 0.51
Copper 0.46 0.71
Magnesium 0.47 0.55
Iron 0.51 0.51
Overstory NMS axis 1 0.60 0.64
Overstory NMS axis 3 0.59 0.67
Natural quality -0.453 -0.433
Percentage topsoil sand (10 cm) -0.300 -0.413
Percentage topsoil clay (10 cm) 0.221 0.316
12 Southeastern Naturalist Vol. 8, Special Issue 2
represented a confounding of disturbance with elevation. Moreover, classifi-
cation of upland sites based on the all-sites analyses or the 2nd/3rd axes of the
upland-only NMS resolved only one “true upland” group plus a group merely
transitional to the mesic sites. We therefore used soil texture (the gradient
expressed by the 1st upland NMS axis) as the basis for instead classifying
upland stands into loamy uplands and clayey uplands (Fig. 3). Treating the
samples in this manner also allowed the classification to be more consistent
with previously developed portions of ECS from adjacent LTAs.
Sites with deep, sandy soils (arenic soils) were not sampled on the
District as we did not locate stands that met minimum-disturbance and age
criteria. However, we encountered early successional and disturbed examples,
usually associated with Flo and Wolfpen soils, during site selection and
sampling. We used LTP descriptions from data for nearby land-type associations
in northern Sabine National Forest, TX (Turner 1999) and the Winn
Ranger District of Kisatchie National Forest (Dehnisch 1998) to describe a
local arenic-soil ecotype.
To observe vegetation of the North Louisiana Clayey Hills in the context
of other West Gulf coastal plain LTAs, we ordinated the Caney District
ground-layer samples with those from the other ECS datasets (DCA eigenvalues
= 0.543 and 0.274 for the first two axes, respectively). Figure 4 shows
the 50 samples from the Caney Ranger District (solid circles) in the context
of the greater ECS data set. Longleaf Pine communities were not encountered
in the North Louisiana Clay Hills: indeed, the area is well north of the
historic distribution of Longleaf Pine (Cruikshank and Eldredge 1939, Frost
1993, Mohr 1897, Williams and Smith 1995); however, the ordination does
clearly show that communities encountered in the Caney District were well
Table 4. Correlations between soil and topographic factors and the axes of a three-dimensional
non-metric multidimensional scaling (NMS) ordination of 20 upland samples and 185 species
from the Caney Ranger District of Kisatchie National Forest based on density-dependant ranked
occurrence of ground layer species. “Fire” is expressed on a scale of 1–10 with 1 = strong evidence
of recent or frequent fire and 10 = no evidence of fire. “Depth to gray mottles” = depth of
soil to gray redox depletions. “Topographic position %” = vertical position of site relative to the
nearest local summit AND steam bottom. The critical value for r is 0.43 for P < 0.05.
NMS Axis
Factor 1 2 3
Percentage topsoil clay (10 cm) -0.53 0.28 -0.08
Percentage clay (50 cm depth) -0.48 0.21 0.21
Percentage clay (100 cm depth) -0.63 0.06 -0.10
Percentage topsoil sand (10 cm) 0.63 -0.13 0.14
Percentage sand (50 cm depth) 0.59 -0.15 -0.18
Percentage sand (100 cm depth) 0.65 0.04 -0.07
Depth to gray mottles 0.75 0.05 0.42
Zinc 0.22 0.43 0.59
Natural quality index -0.13 -0.28 -0.76
pH 0.62 -0.17 -0.34
Fire -0.04 -0.55 -0.68
Topographic position % -0.01 0.19 0.54
Elevation (m) 0.04 0.64 0.77
2009 J.E. Van Kley and R.L. Turner 13
within the fl oristic range of equivalent communities from other portions of
the West Gulf Coastal Plain.
Figure 3. A three-dimensional NMS ordination of 20 upland samples and 185 species
from the Caney Ranger District of Kisatchie National Forest based on mean rankedoccurrence
values for ground layer species. Axes 1 and 3 are displayed. Monte Carlo
P = 0.02, Final “stress” = 10.7, final instability = 0.00001. Solid and open shapes
represent sites with >35% and <35% clay at 50 cm depth respectively; the resulting
soil-texture based classification of samples forms the basis for describing upland ecological
units. Squares and triangles represent a TWINSPAN-derived classification of
samples, respectively, into Shortleaf Pine- and Loblolly Pine-dominated communities
also presented in Figure 2 and Appendix 1. Right triangles represent 2 “borderline”
mesic sites (separated from other samples in ordination space by low 2nd axis
scores). “Joint plot” lines indicate the direction and relative strength of correlations
between ordination scores and external factors (minimum r2 for joint-plot display =
0.23). Actual correlations are shown in Appendix 1. “Less Fire” is expressed on a
scale of 1–10: 1 = strong evidence of both recent or frequent fire and 10 = no evidence
of fire. “MoDepth” = depth of soil to gray redox depletions. “Clay 10,” “clay 50,”
and “clay 100” represent the percentage of clay-sized mineral particles in the soil at
depths of 10, 50, and 100 cm respectively. “Sand 10,” “sand 50,” and “sand 100”
represent the percentage of sand-sized mineral particles in the soil at depths of 10, 50,
and 100 cm respectively. “-NQ”= “natural quality” on a scale of 1–12: higher values
= more evidence of disturbance and lower quality. “T_Pos%” = topographic position
% = vertical position of site relative to the nearest local summit and steam bottom.
14 Southeastern Naturalist Vol. 8, Special Issue 2
Table 5. A dichotomous key to the land-type phases of the North Louisiana Clayey Hills. Species
groups, described in Van Kley et al. (2007), are cross-referenced to their closest equivalents
in this paper in Appendix 1.
1a. Upper slopes, broad uplands, or ridgetops. Sites are typically pine-dominated 2
1b. Lower slopes, ravines, hillside seeps, stream terraces, or stream fl oodplains. Sites are
typically deciduous hardwood-dominated. 4
2a. Soils are arenic (sandy surface layer more than 50cm thick) or sandy throughout the
profile. Soils usually mapped as Flo or Wolfpen. The Tragia species group may be present.
231Ea.9.1.20 Shortleaf Pine-Blackjack Oak/ Tragia Sandy Dry Uplands
2b. Soils are loamy or clayey; any sandy surface layer is <50 cm thick. 3
3a. Soils are either loamy throughout or have a sandy loam, loamy sand, or gravelly surface
layer more than 30 cm thick over clay subsoil. Often mapped as Darley, Ruple, Mahan, Bowie,
Darbonne, or Angie. Species from the Callicarpa and Chasmanthium groups are abundant.
231Ea.9.1.30 Shortleaf Pine-Southern Red oak/
Callicarpa-Chasmanthium Loamy Dry-Mesic Uplands
Figure 4. A DCA ordination 420 sample sites and 815 species representing the combined
ECS datasets based on ground layer mean ranked occurrence. All samples,
including those from the Caney were active in the ordination solution. Disjunct
samples from non-forest prairies, glades, and other open communities were removed
prior to analysis. Eigenvalues were 0.543 and 0.274 for axes 1 and 2 respectively.
Samples from the Caney Ranger District of Louisiana’s Kisatchie National Forest
(solid circles) are shown in context of plant communities from other regions of the
West Gulf Coastal Plain.
2009 J.E. Van Kley and R.L. Turner 15
Table 5, continued.
3b. Any loamy surface soil is less than 30 cm thick over clay subsoil. Soils are somewhat
poorly drained and usually have shrink-swell properties. Gray drainage mottles may be present
and a perched water table may occur. Includes most areas mapped as Sacul and Eastwood
soils. Species from the Callicarpa and Chasmanthium groups are abundant.
231Ea.9.2.10 Shortleaf Pine/ Chasmanthium Clayey Dry-Mesic Uplands
4a. Moderate to steep lower slopes and ravines or minor stream terraces. Species from the
Callicarpa, Chasmanthium, and Mitchella groups are common but the Bignonia and Justicia
groups are rare or absent.
231Ea.9.3.10 White Oak-American Beech-Loblolly Pine/
Chasmanthium Loamy Mesic Lower Slopes
4b. Valleys and fl oodplains of small or medium-sized intermittent or perennial streams or
areas of groundwater seepage. 5
5a. Constantly saturated groundwater seepage areas (baygalls) at the head of or along small
streams. Deep, gray, nearly permanently saturated, sandy loam soils. Soils belong to the Osier
series. Magnolia virginiana L. (Sweetbay Magnolia), Nyssa bifl ora Walt. (Swamp Tupelo),
and Acer rubrum L. (Red Maple) dominate the overstory. Ilex decidua Walt. (Possumhaw),
Rhododendron prinophyllum (Small) Millais (Early Azalea), andVaccinium fuscatum Ait.
(Arkansas Blueberry) are common in the understory. The Osmunda group is common.
231Ea.9.4.30 Sweetbay-Swamp Tupelo/ Osmunda Sandy Wet Forested Seeps
5b. Stream bottoms or fl oodplains without significant surface seepage of groundwater, the
Osmunda group absent. 6
6a. Small intermittent or perennial stream fl oodplains typically less than 100 m wide. Flooding
is intermittent and sites generally fl ood for less than 5% of the growing season. Soils are
commonly mapped as Iuka soils or as the soil type of adjacent uplands. Overstory includes
Quercus nigra L. (Water Oak), Liquidambar styracifl ua L. (Sweetgum), Pinus taeda L.
(Loblolly Pine), and often Fagus grandifolia Ehrh. (American Beech). The Chasmanthium,
Callicarpa, and Mitchella groups are common; species from the Bignonia and Justicia groups
are rare.
231Ea.9.4.10 Water Oak/ Mitchella Loamy Mesic Strea Bottoms
6b. Floodplains of medium-sized or large perennial streams, fl oodplains more than 100 m
wide. Flooding is irregular or seasonal; sites are fl ooded for more than 5% of the growing season.
Soils are commonly mapped as Guyton or Iuka. Flood-tolerant species such as Quercus
michauxii Nutt. (Swamp Chestnut Oak), Quercus phellos L. (Willow Oak), Ulmus Americana
L. (American Elm), and Quercus laurifolia Michx. (Laurel Oak) are often present. Members
of the Bignonia and Justicia groups are usually present. 7
7a. Floodplains are irregularly fl ooded (fl ood for <12.5% of a typical growing season).
Seasonally fl ooded (12.5–25% of season) areas exist as small, isolated areas in depressions.
Members of the Chasmanthium, Callicarpa, and Mitchella groups are common. Overstory is
a variable mixture of mesic and fl ood tolerant species, but Swamp Chestnut Oak, Water Oak,
and Loblolly Pine may be common.
231Ea.9.4.20 Sweetgum-Oak/ Bignonia Loamy Wet-Mesic Stream Bottoms
7b. Floodplains are largely seasonally fl ooded (12.5–25% of a typical growing season) or if
fl ooded less, exist on a landscape with a significant seasonally fl ooded component. Swampy
areas with Bald Cypress may also occur. In Kisatchie National Forest’s Caney Ranger
District, restricted to the lowest, most downstream parts of the fl oodplains of Corney Bayou
and the Middle Fork of Bayou D’Arbonne. Tbese areas lack the Chasmanthium, Callicarpa,
and Mitchella groups, but the Bignonia and Justicia groups are common. Flood-tolerant oaks
(Willow, Laurel, and Quercus lyrata Walt. [Overcup]) often dominate.
231Ea.4 Alluvial Floodplains and Terraces Landtype Association
16 Southeastern Naturalist Vol. 8, Special Issue 2
The results enabled us to circumscribe seven land-type phases for the
North Louisiana Clayey Hills (Table 5). The classifications of Appendix
1 for non-uplands and of Figure 3 for upland samples formed the basis for
the LTPs. Dichotomous keys (Table 5) and detailed data-derived descriptions
of the topography, soils, hydrology, known natural disturbances and
processes, ground-layer species, overstory, understory trees, and shrubs for
each land-type phase were generated. Each LTP is named after dominant
overstory species, a characteristic ecological species group, a soil or hydrologic
feature, and its typical topographic position (Table 5). The ecological
species groups in the names and keys (Table 5) are the pooled “master”
species groups of Van Kley et al. (2007), but they mainly correspond to the
TWINSPAN-derived species classification of Appendix 1 which “crosswalks”
its species classification with the “master” species groups. LTPs
were aggregated into four land-types: 231Ea.9.1 (sandy/loamy uplands),
231Ea.9.2 (clayey uplands), 231Ea.9.3 (mesic slopes and terraces), and
231Ea.9.4 (minor stream bottoms).
The unique code for a LTP (Table 5) incorporates the symbols or numbers
for all ecological units of the hierarchichy in which it is nested. For example,
the Caney Ranger District of Kisatchie National Forest is within the
Southeastern Mixed Forest Province (231), the South Central Arkansas Subsection
(231Ea), and the North Louisiana Clayey Hills LTA (231Ea.9; Fig. 1).
Upland sites with loam soils belong to the Sandy/Loamy Uplands Landtype
(231Ea.9.1) and the “Shortleaf Pine-Quercus falcata Michx. (Southern Red
Oak)/Callicarpa (beautyberry spp.)-Chasmanthium (woodoats spp.) Loamy
Dry-Mesic Uplands” Landtype Phase (231Ea.9.1.30). Keys and LTP descriptions
provided for each LTA comprise the bulk of the ECS fieldguide (Van
Kley et al. 2007). Figure 5 summarizes the main features of the Caney LTPs.
Two wet, low fl oodplain terraces and a Baldcypress swamp associated with
the larger downstream fl oodplains of Corney Bayou and Bayou D’Arbonne,
were interpreted as a result of the ordination in Figure 4 as belonging to the
adjacent Alluvial Floodplains and Terraces land-type association; data from
those sites contributed to descriptions of ecotypes of alluvial LTAs rather
than those of the North Louisiana Clay Hills (Table 5 - couplet 7b).
Discussion
The complete ECS effort of which the samples from the Caney Ranger
District are only a part consisted of 462 sample sites, 956 species, and 11
separate data sets representing the 18 land-type associations of the region
(Table 6). Results from the various data sets generally yielded similar results:
topographic position, percentage of soil sand and clay, nutrients, fire history
(when available), and hydrologic factors (depth to gray mottles, high-water
marks, fl ood depth) were among those most consistently and strongly correlated
with vegetation gradients (Table 6). Accordingly, we emphasized these
factors when describing environmental components of ecological units.
2009 J.E. Van Kley and R.L. Turner 17
ECS results are largely supported by local literature. Marks and Harcombe
(1981) related woody plant communities from the Big Thicket area
of southeast Texas to environmental gradients. Compositional variation correlated
primarily with percentage of sand in the surface soil and secondarily to
aspects of soil fertility. Harcombe et al. (1993) examined plant communities
in the Longleaf Pine region of the West Gulf Coastal Plain. Vegetation corresponded
to a soil-texture gradient which appeared to co-vary with soil depth
and topography, both of which may infl uence soil moisture more strongly
than texture alone. Nixon et al. (1987) described changes in woody vegetation
along a topographic and soil gradient from an east Texas creek bottom to an
upland. Soil texture and topography were likewise important factors in most
ECS datasets (Table 6). Bridges and Orzell (1989) conducted a qualitative assessment
that identified four subtypes of upland Longleaf Pine woodlands and
three subtypes of wet savanna Longleaf Pine communities; ECS generally resolved
two types in most LTAs: one on sandy soils and one on loam. Wet pine
savannas lie mainly outside (south) of the ECS study region.
Figure 5. A landscape profile showing characteristic topographic position and summarized
soils and natural vegetation for seven ecological units (land-type phases) for
the North Louisiana Clayey Hills. Names corresponding to the codes for the units are
in Table 5. The unique code for each land-type phase indicates the ecological units
of the hierarchy in which it is nested: the LTPs shown are in the Southeastern Mixed
Forest Province (231), the South Central Arkansas Subsection (231Ea), and the North
Louisiana Clayey Hills Landtype Association (231Ea.9). Species group names refer
to the “master” combined ecological species groups of Van Kley et al. 2007; their
closest equivalents from the current study are shown in Appendix 1.
18 Southeastern Naturalist Vol. 8, Special Issue 2
Table 6. Summary of the datasets used to develop ECS for the West Gulf Coastal Plain showing numbers of sample stands, LTAs covered, analyses used, selected
correlations between ordinations and environmental factors, and the publication, report, or thesis in which the data were originally presented. The Red
River Alluvial Plain and Alazan Wildlife Management Area ordinations were based on overstory; all others shown in the table used ground layer vegetation.
P > 0.05 for all reported correlations. Locations of the forests sampled are shown in Figure 1. CCA and DCCA are described in Ter Braak and Smilaur (2002).
NF = national forest; RD = ranger district.
Dataset, location, Ordination axis (1, 2, or 3) and
and year sampled Land-type association(s) Sites Type of analysis environmental factor correlations (r) Publication
1) Kisatchie NF: Calcascieu Ft. Polk Rolling Uplands; 47 DCA Topographic position (1) r = -0.84; Van Kley 1999b
and Catahoula RD (1994) High Terrace Rolling Uplands Fire frequency (1) r = -0.91;
Nitrogen (1) r = 0.51;
Phosphorus (1) r = 0.64;
Sand (2) r = 0.61;
Clay (2) r = -0.47
2) Angelina and Davy Crockett Western Clayey Uplands; 51 Hybrid DCA/ Sand (1) r =0.78; Van Kley, unpubl.
National Forests (1994) Eastern Clayey Uplands DCCA Clay (1) r = -0.58; data
Calcium+ Magnesium (1) r = -0.57;
Topographic position (2) r = 0.65
3) Kisatchie NF: Kisatchie RD Kisatchie Sandstone Hills 51 Hybrid DCA/ Topographic position (1) r = -0.83; Van Kley 1999a
(1995) DCCA Sand (2) r = 0.63;
Calcium (2) r = -0.47
4) Caddo Lake Wildlife Mgt. Alluvial River Floodplains 30 DCA Water depth during fl ood stage (1) Van Kley and Hine
Area (1995) r = 0.86 1998
5) Kisatchie NF: Winn and Rolling Clayey Uplands; 39 DCA Topographic position (1) r = -0.76; Dehnisch 1998
Catahoula RD (1996) Winn Rolling Uplands Sand (2) r = -0.39;
Clay (2) r = 0.49;
Clay (3) r = 0.51
6) Sam Houston National San Jacinto Flatwoods; 54 DCA Topographic position (1) r = 0.36 Van Kley and Turner,
Forest (1996) Raven Hills; Western Big (2) r =-0.55; Unpubl. data
Thicket Elevation (2) r = -0.69;
Slope steepness (1) r = 0.49;
Sulfur (2) r = 0.40
2009 J.E. Van Kley and R.L. Turner 19
Table 6, continued.
Dataset, location, Ordination axis (1, 2, or 3) and
and year sampled Land-type association(s) Sites Type of analysis environmental factor correlations (r) Publication
7) Combined national forests LTAs listed for datasets 2 164, CCA Topographic Position (1) r = 0.45, Turner 1999
in Texas: All samples from and 6; Mayfl ower Uplands; (59 new) (2) r = -0.49;
data-sets 2 & 6 plus 59 Sandy Uplands; Redlands; Depth to gray mottles (1) r = 0.48;
samples mainly from Lignitic Uplands Sand (3) r = 0.48; pH (2) r = 0.36, (3) r = 0.34;
Angelina and Sabine NF N (3) r =- 0.50; K (3) r = -0.32;
(1995-1996) Mg (3) r = 0.33); S (3) r = 0.33;
Latitude (3) r = -0.70;
Longitude (1) r = 0.54, (3) r = -0.37;
Mean low Temperature (1) r = -0.39;
Mean Evaporation (1) r = -0.51
8) SFA Experimental Forest, Alluvial River fl oodplains 33, DCA High water mark height (1) r = -0.83; Mundorf 1998
Angelina, Davy Crockett, (21 new) % bare (litterless) soil surface (1) r = -0.82;
and Kisatchie NF: incl. 12 Soil color: less “grayness" (1) r = 0.68;
samples from other datasets (1996) Sand (1) r = 0.53; Clay (1) r = -0.62
9) Alazan Bayou Wildlife Alluvial River fl oodplains; 41 DCA Topographic position (1) r = 0.67; Quine 2000
Management Area (1999) Redlands Elevation; (1) r = 0.69;
High water mark height (1) r = -0.79;
Depth to gray mottles (1) r = 0.73
10) Kisatchie NF: Caney RD North Louisiana Clayey Hills; 50 NMS Topographic position (1) r = -0.53, Van Kley, previously
(2002) Caney Lakes Rolling Uplands (2) r = -0.78; unpubl. data:
Fire evidence (1) r = 0.57, (2) r = 0.74; current paper
Depth to gray mottles (1) r = -0.76;
Additional information: Table 3, Figure 2.
11) Kisatchie NF: Calcascieu, Red River Alluvial Plain 19 NMS Estimated fl ood regime (1) r = 0.47, Van Kley et al. 2007;
Catahoula, and Kisatchie RD (3) r = 0.61; Van Kley, unpubl.
plus selected non-USFS lands Soil drainage (3) r = 0.86; data
(2004) Topographic Position; (3) r = 0.72
Total 462
20 Southeastern Naturalist Vol. 8, Special Issue 2
Most published descriptions of individual local plant communities also
had counterparts in the ECS results. Dry uplands described by Marietta
(1979), Marietta and Nixon (1983), and Ward and Nixon (1992) correspond
to communities that develop on the arenic (and grossarenic) dry upland LTPs
of Van Kley et al. 2007. Mesic forest communities of Nixon et al. (1980) and
beech-hardwood forests of MacRoberts and MacRoberts (1997) typically
occur on the ECS mesic slope and mesic stream bottom LTPs. Brooks et al.
(1993) describe two types of “wet creek bottoms” for eastern Texas, a northern
type and a southern one. Called “forested seeps” in ECS, and “Baygalls”
by MacRoberts and MacRoberts (2004), those on the Caney District were of
the northern type. Chambless and Nixon (1975), Nixon and Raines (1976),
and Nixon et al. (1977) and describe bottomland forest communities which
correspond to the vegetation component of ECS wet-mesic and seasonally
fl ooded fl oodplain LTPs.
A total of 137 land-type phases in 18 land-type associations are described
in the current ECS field guide (Van Kley et al. 2007). However, the
rigid nature of the National ECS hierarchy belies the occurrence of strikingly
similar land-types and land-type phases across the different LTAs
(see Fig. 4). The chief difference between many LTAs was the distribution
of ecological types within them or the presence and absence of “unusual”
types such as glades and prairies rather than major differences in the dominant
types. Principal exceptions include the well-documented absence of
Longleaf Pine communities in the northern and western part of the West
Gulf coastal plain (Fig. 4) and the obvious restriction of most wetland LTPs
to floodplain LTAs. Although some variation in species composition was
associated with larger-scale geographic variables (Turner 1999), communities
and ecotypes described in one LTA had close analogues in most others
(see Fig. 4); the ECS data provide no strong support for the current LTA
subdivisions. Of all ECS levels, the current LTAs with their strong geology
emphasis, are the closest to being a single-component classification. Additional
investigation may re-define (and possibly combine several) LTAs
to be more relevant to documented differences in vegetation across the region.
Recognizing this issue, Van Kley et al. (2007) describe 18 LTP-level
“general ecological types” applicable across most of the West Gulf Coastal
Plain that largely correspond to the ecosystem-type descriptions in the introduction
to Volume 1of the Illustrated Flora of East Texas (Van Kley, in
Diggs et al. 2006).
ECS currently covers a large part of the West Gulf Coastal Plain at the
LTP level, and is becoming a valuable conservation, management, and inventory
tool. Its chief advantage over existing single-attribute
classifications is that it integrates multiple ecosystem components into the
classification thereby forming an expression of the “ecological potential”
of the land: sites classified as the same ecological unit should respond in
similar ways to most forms of management, support similar old-growth and
late-successional plant communities, and support a similar array of seral
communities and succession pathways. Nonetheless, vegetation-only
2009 J.E. Van Kley and R.L. Turner 21
classifications such as The Nature Conservancy's US National Vegetation
Classification (Allard 1990, Anderson et al. 1998, Grossman et al. 1998) or
the Texas plant community classification framework (Diamond et al. 1987)
have an important role, especially in the number of finely-defined community
types they resolve; cross-walking vegetation-based types with the
ecological land units of ECS will enhance the usefulness both ECS and
the vegetation classifications.
In addition to being a management and inventory tool, ECS provides a
framework for ecological research. Huston (2007) used ECS as a framework
to describe bryophyte communities for the principal east Texas ecological
types, and Fakhritidinova (2008) used molecular methods to describe community
patterns of arbuscular mycrorrhizal fungi on three widespread native
host plants across contrasting east Texas ecological types.
A high future priority is generating LTP maps on US Forest service lands.
Mapping allows ECS to reach its full potential as a basis for decision making
and planning. Other needs include continued testing and refinement of
existing ecological units and extending the geographic coverage of ECS. In
particular, the Big Thicket National Preserve in southeastern Texas, an area
for which there is rich preexisting data (Marks and Harcombe 1981, etc.)
that could be tapped, forms a major gap in present ECS coverage. Describing
possible succession pathways and additional components of the ecosystem
such as bryophytes, soil microbes, insects, and mycorrhizal fungi for the
ecological units will also greatly enhance the power of ECS.
Acknowledgments
Numerous individuals and organizations contributed to this large, multi-year
project. We thank The Nature Conservancy, the US Forest Service, and Stephen F.
Austin State University for multiple seasons of funding. Assistance was provided by
numerous staff from The Nature Conservancy, the National Forests and Grasslands
in Texas, Kisatchie National Forest, and other agencies. Ike McWhorter and Bill
Bartush helped define the scope of this project and provided administrative support.
Philip Hyatt, John Novosad, Susan Carr, David Moore, and Calvin Baker of
Kisatchie National Forest provided administrative and logistical support. Guy Nesom
assisted with site selection and data collection on Sam Houston National Forest.
Kevin Mundorff, Mike Dehnisch, John Quine, and Matthew Welch collected and
analyzed field data while pursuing graduate degrees at Stephen F. Austin State University.
Dr. Larry Brown helped with plant identification. Raymond Dolezel’s aid in
classifying soils was greatly appreciated. We thank Dr. Scott Beasley of the College
of Forestry, Stephen F. Austin State University, for use of the GIS Laboratory and Dr.
Paul Harcombe, Alan Weakley, and Jim Keys, for their helpful suggestions. Finally,
we acknowledge Forest Supervisors Alan Newman, Danny Britt, Ronnie Raum, Lynn
Neff, Fred Salinas, and Gretta Boley for their support of ECS.
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26 Southeastern Naturalist Vol. 8, Special Issue 2
Appendix 1. A synoptic table derived from a TWINSPAN classification of 50 samples and 340 species from the Caney Ranger District of
Kisatchie National Forest. Values = mean occurrence rank (frequency %). Only species with mean occurrence >1.8 in at least one community
are displayed. SOU= Shortleaf Pine-oak-hickory uplands, LSU = Loblolly Pine-Sweetgum uplands, MLS = mesic lower slopes and stream
bottoms, WMF = wet-mesic fl oodplains, WMT = wet-fl oodplain terraces, FS = forested seeps, and SWP = Baldcypress swamp. Species group
names in parenthesis indicate the “master” ecological species group(s) of Van Kley et al. 2007 to which the Appendix 1 group is closest.
Species SOU LSU MLS WMF WMT FS SWP
Species of upland pine oak-hickory communities (“Tragia + Schizachyrium groups”)
Carya texana Buckl. 2.5 (64) 1.9 (43) 0.7 (17) - - - -
Desmodium paniculatum (L.) DC. 1.9 (64) 1.1 (43) - - - - -
Dichanthelium acuminatum (Sw.) 2.0 (64) 0.3 (14) - 0.8 (25) - -
Gould & C.A. Clark
Euphorbia corollata L. 3.5 (91) 0.7 (29) 0.1 (6) - - - -
Galactia volubilis (L.) Britt. 2.0 (64) 0.4 (29) - - - - -
Hypericum hypericoides (L.) Crantz 3.1 (100) 0.4 (14) 0.5 (33) 0.8 (25) - - -
Lespedeza violacea (L.) Pers. 1.5 (45) - - - - - -
Pinus echinata P. Mill. 3.0 (82) 0.1 (14) 0.2 (6) - - - -
Pteridium aquilinum (L.) Kuhn 1.8 (45) - 0.7 (28) - - - -
Quercus stellata Wangenh. 1.8 (45) - - - - - -
Rhus copallinum L. 2.7 (91) 0.9 (43) 0.1 (6) - - - -
Vaccinium arboreum Marsh. 3.9 (100) 2.3 (86) 0.8 (39) - - - -
Vernonia texana (Gray) Small 1.9 (64) - - - - - -
Viburnum rufidulum Raf. 2.8 (91) 1.1 (43) 0.9 (44) - - - -
Species of upland and mesic sites (“Callicarpa group”)
Aesculus pavia L. 2.4 (73) 0.7 (29) 1.1 (56) - - - -
Celtis laevigata Willd. 0.4 (18) 2.0 (71) 0.5 (17) - - - -
Callicarpa americana L. 3.9 (100) 3.4 (100) 3.6 (94) 1.4 (75) - 3.7 (100) -
Chionanthus virginicus L. 2.6 (82) 1.7 (71) 1.7 (67) - - 2.3 (100) -
2009 J.E. Van Kley and R.L. Turner 27
Species SOU LSU MLS WMF WMT FS SWP
Clitoria mariana L. 2.4 (73) 2.6 (86) 0.8 (39) - - - -
Cornus fl orida L. 2.9 (100) 3.3 (86) 2.4 (89) 0.4 (25) - 1.7 (67) -
Desmodium obtusum (Muhl ex. Willd) DC 3.0 (100) 3.0 (100) 1.9 (61) 0.4 (13) - - -
Dioscorea quaternata J.F. Gmel. 0.4 (18) 0.9 (29) 2.2 (72) - - - -
Fraxinus americana L. 1.1 (45) 0.4 (29) 2.2 (83) 0.3 (25) - 1.0 (33) -
Frangula caroliniana (Walt.) Gray 1.0 (45) 4.0 (100) 1.9 (78) 0.3 (13) - 0.7 (33) -
Gelsemium sempervirens St.-Hil. 2.5 (73) 2.7 (86) 0.5 (17) - - - -
Hamamelis virginiana L. 0.7 (27) 1.0 (29) 3.8 (100) 0.4 (13) - 1.3 (33 -
Ostrya virginiana (P. Mill.) K. Koch 1.1 (27) 1.1 (43) 3.2 (94) - - 1.3 (33 -
Prunus serotina Ehrh. 3.8 (100) 3.6 (100) 3.1 (89) 0.3 (13) - 0.7 (33) -
Quercus alba L. 4.0 (100) 3.4 (100) 3.6 (94) - - 3.3 (100) -
Quercus falcata Michx. 3.1 (82) 3.6 (100) 1.5 (56) 1.1 (25) - 0.7 (33) -
Sassafras albidum (Nutt.) Nees 2.4 (64) 3.1 (100) 3.1 (94) 0.3 (13) - - -
Scleria oligantha Michx. 3.3 (100) 2.6 (57) 1.9 (56) - - 0.3 (33) -
Smilax bona-nox L. 3.5 (91) 1.7 (43) 1.3 (44) 0.6 (25) - 1.0 (33) -
Smilax smallii Morong 2.0 (64) 1.0 (29) 1.0 (39) 0.3 (13) - - -
Vaccinium virgatum Ait. 3.8 (100) 2.9 (86) 2.2 (56) 0.1 (130 - - -
Viburnum dentatum L. 3.1 (91) 0.7 (29) 1.7 (56) - - 1.0 (33) -
Vitis aestivalis Michx. 2.5 (91) 3.4 (100) 2.7 (94) 2.1 (88) - - -
Wide-ranging species (“Chasmanthium + Mitchella groups”)
Acer rubrum L. 3.6 (91) 4.7 (100) 3.7 (94) 1.3 (50) 3.5 (100) 3.3 (100) 1.0 (100)
Berchemia scandens (Hill) K. Koch 0.9 (45) 2.0 (57) 1.1 (39) 2.6 (88) - 1.7 (67) -
Bignonia capreolata L. 1.8 (64) 1.7 (57) 3.2 (100 4.1 (100) 2.0 (50) 3.3 (100) -
Chasmanthium sessilifl orum (Poir.) Yates 4.5 (100) 4.6 (100) 2.7 (78) 0.1 (13) - - -
Chasmanthium laxum (L.) Yates 0.3 (9) 0.3 (14) 1.8 (44) 3.1 (88) 3.5 (100) 3.7 (100) -
Dichanthelium dichotomum (L.) Gould 1.5 (55) 0.1 (14) 0.4 (17) 2.0 (63) 0.5 (50) 2.7 (67) -
28 Southeastern Naturalist Vol. 8, Special Issue 2
Species SOU LSU MLS WMF WMT FS SWP
Dichanthelium boscii (Poir.) Gould & 3.2 (82) 2.1 (57) 3.1 (89) 3.4 (88) - 1.3 (33) -
C.A. Clark
Diospyros virginiana L. 1.4 (82) 2.0 (57) 0.8 (33) 0.5 (25) 3.0 (100) - -
Ilex opaca Ait. 1.2 (55) 2.9 (100) 3.4 (94) 2.6 (75) 2.5 (100) 3.7 (100) -
Liquidambar styracifl ua L. 3.3 (82) 2.9 (71) 1.6 (67) 2.4 (75) 3.5 (100) 2.3 (67) -
Lonicera japonica Thunb. 0.5 (18) 2.4 (86) 1.6 (50) 1.3 (38) - 2.3 (67) -
Wide-ranging species (“Chasmanthium + Mitchella groups”)
Mitchella repens L. 1.8 (55) 2.4 (86) 2.2 (67) 4.1 (100) 2.5 (100) 2.7 (67) -
Nyssa sylvatica Marsh. 3.1 (91) 3.3 (100) 2.9 (94) 2.8 (100) 3.0 (100) 2.3 (100) -
Parthenocissus quinquefolia (L.) Planch. 3.8 (91) 4.7 (100) 4.4 (100) 2.0 (63) - 2.0 (100) -
Pinus taeda L. 1.2 (36) 1.9 (57) 1.7 (61) - 3.5 (100) 2.7 (67) -
Polystichum acrostichoides (Michx.) Schott 0.1 (9) 0.9 (43) 2.6 (72) 0.5 (13) - - -
Quercus nigra L. 2.9 (73) 4.3 (100) 3.4 (89) 2.9 (75) 4.0 (100) 3.0 (100) -
Rubus argutus Link 0.8 (27) 1.4 (43) 0.7 (22) 2.6 (75) 1.0 (50) 2.0 (67) -
Smilax glauca Walt. 3.5 (100) 3.6 (100) 3.4 (100) 2.6 (88) 2.5 (100) 2.3 (67) -
Smilax rotundifolia L. 1.9 (55) 2.1 (57) 2.3 (67) 3.3 (88) 3.5 (100) 4.0 (100) -
Toxicodendron radicans (L.) Kuntze 3.9 (91) 4.9 (100) 4.0 (100) 4.4 (100) 1.5 (50) 2.3 (67) -
Trachelospermum difforme (Walt.) Gray 0.3 (9) 0.3 (29) 0.3 (11) 2.5 (88) 1.5 (50) - -
Ulmus alata Michx. 1.7 (64) 3.1 (100) 2.7 (83) 1.8 (75) - 0.7 (33) -
Vaccinium elliottii Chapman 0.1 (9) 1.7 (57) 1.0 (33) 1.0 (38) 3.5 (100) - -
Vitis rotundifolia Michx. 4.5 (100) 4.4 (100) 4.3 (100 3.9 (100) 1.0 (50) 4.0 (100) -
Species of mesic, wet-mesic, and forested seep sites (“Arisaema group”)
Acer barbatum Michx. - 0.6 (29) 1.9 (50) 0.9 (25) - - -
Arisaema triphyllum (L.) Schott - 1.4 (57) 1.7 (33) 0.9 (38) - 3.7 (100) --
Athyrium filix-femina (L.) Roth - 0.3 (14) 0.6 (17) 0.8 (38) - 4.7 (100) -
Carpinus caroliniana Walt. - 1.6 (43) 2.2 (61) 3.6 (100) 1.0 (50) 1.7 (67) -
Carex abscondita Mackenzie - 0.1 (14) 1.5 (39) 4.0 (88) - - -
2009 J.E. Van Kley and R.L. Turner 29
Species SOU LSU MLS WMF WMT FS SWP
Euonymus americana L. - 0.3 (14) 2.5 (89) 1.1 (38) - 1.0 (33) -
Fagus grandifolia Ehrh. - 1.7 (71) 2.2 (67) 0.5 (25) - 2.0 (67) -
Ligustrum sinense Lour. - 0.3 (14) 0.1 (6) 1.6 (88) - 2.3 (100) -
Quercus laurifolia Michx. - 0.3 (14) 0.3 (11) - 4.5 (100) 1.0 (33) -
Quercus michauxii Nutt. - 1.1 (29) 0.5 (17) 1.8 (63) 1.5 (50) 0.3 (33) -
Species of fl oodplains and wetlands (“Bignonia + Justicia groups”)
Arundinaria gigantea (Walt.) Muhl. - - 0.3 (11) 2.0 (63) - - -
Bidens aristosa (Michx.) Britt. - - 0.2 (6) 1.5 (75) - - 5.0 (100)
Boehmeria cylindrica (L.) Sw. - - 0.3 (17) 2.6 (75) 1.5 (50) 2.0 (67) 4.0 (100)
Brunnichia ovata (Walt.) Shinners - - - 2.4 (75) 2.0 (50) - 2.0 (100)
Carex debilis Michx. - - 1.1 (28) 1.9 (50) 1.5 (50) 4.3 (100) -
Carex fl accosperma Dewey - - 0.3 (17) 2.0 (63) 1.5 (50) - -
Carex joorii Bailey - - 0.2 (6) - 4.5 (100) - 4.0 (100)
Carex louisianica Bailey 0.4 (9) - 0.2 (6) 3.8 (100) 2.5 (100) - 1.0 (100)
Carya glabra (P. Mill.) Sweet - - 1.7 (39) 2.1 (50) - - -
Cephalanthus occidentalis L. - - - 1.3 (63) - 2.0 (67) 5.0 (100)
Commelina virginica L. - - 0.2 (6) 2.9 (100) - - -
Itea virginica L. - - 0.2 (6) 0.4 (25) - 3.3 (100) 4.0 (100)
Justicia ovata (Walt.) Lindau - - 0.5 (17) 1.8 (63) - - -
Leersia oryzoides (L.) Sw. - - 0.2 (6) 1.9 (50) - - -
Leersia virginica Willd. - - 0.6 (22) 2.0 (63) - 1.7 (67) -
Lycopus rubellus Moench - - 0.1 (6) 1.0 (38) - 2.0 (67) 4.0 (100)
Quercus phellos L. - - 0.2 (6) 1.4 (38) 2.0 (50) - -
Saururus cernuus L. - - 0.1 (6) 2.1 (88) 2.5 (100) 2.0 (67) 2.0 (100)
Styrax americanus Lam. - - - 0.5 (25) 3.5 (100) - 4.0 (100)
Species of forested seeps ('”Osmunda group”)
Magnolia virginiana L. - - 0.1 (6) - 1.0 (50) 3.7 (100) -
Osmunda cinnamomea L. - - - - - 2.6 (100) -
30 Southeastern Naturalist Vol. 8, Special Issue 2
Species SOU LSU MLS WMF WMT FS SWP
Viburnum nudum L. - - - - - 4.0 (100) -
Woodwardia areolata (L.) T. Moore - - 0.1 (6) - - 4.7 (100) -
Wetland species (“Ceratophyllum group”)
Hydrolea unifl ora Raf. - - - - - - 2.0 (100)
Lemna valdiviana Phil. - - - - - - 4.0 (100)
Ludwigia glandulosa Walt. - - - - - - 2.0 (100)
Planera aquatica J.F. Gmel. - - - - - - 3.0 (100)
Proserpinaca palustris L. - - - - - - 4.0 (100)