THE VASCULAR FLORA OF THE NORTH CENTRAL TEXAS WALNUT FORMATION

2012·16 MB·English

by  Rebecca K Swadek

THE VASCULAR FLORA OF THE NORTH CENTRAL TEXAS
WALNUT
FORMATION
Swadek
Rebecca Tony
Burgess
K.
L.
Texas Christian University Texas Christian University
Botanical Research Institute of Texas TCU Box 298830
700 University Drive Fort Worth, Texas 76 129, U.S.A
1
Fort Worth, Texas 76 107-3400, U.S.A. [email protected]
ABSTRACT
Jii
INTRODUCTION
have been defined by political boundaries
In Texas, few have been published, and these traditionally
floras
&
and Manual
such as Neill’s flora of Madison County, Texas (Neill Wilson 2000). Correll Johnston’s of the
published 42 years ago. Floras completed in Texas are
Vascular Plants Texas the only statewide flora,
of (1970) is
These
seldom and many languish as theses hidden in university libraries.
published peer-reviewed journals,
in
While
ecological data.
lacking detailed
during the survey,
are encountered
often merely
checklists of species
information.
with associated ecological
possible
checklists more useful insights are
are critical baselines,
determinant vegetation.
geology often a strong for
Cuyler and Tharp both stated that is
(1931) (1939)
on
and landform plant
geology
importance of
Kruckeberg an impeccable argument for the
provides
(2004)
data—
information often valuable
include geological
communities. and herbarium specimens rarely
Yet, floras
by works and
context inspired these
for This study has a geological
understanding and endemic
species.
rare
the endemic (Comanche Peak prairie clover).
Dalea
reverchonii
m
on Comanche Peak
was
collected
North Central Texas, first
Dalea endemic
to
reverchonii (Fabaceae),
was not found
Hood described as Petalostemum reverchonii, it
County, 1876 by Reverchon. Originally
Julien
almost
revealed that D. reverchonii is re-
Subsequent collections
“gain
until the 1980s (Mahler 1984).
early
nted comm.). This contradicts Poole
(O’Kennon
Formation pers.
Walnut
to rocky glades and barrens of the
726
et (2007), who stated D. reverchanii is observed only on Goodland Limestone. There is one exception: at the
al.
on Comanche Peak, the only population found south of the Brazos River, D. revercho-
type the butte of
locality
may
grows on Edwards Limestone; thus is not strictly endemic to the Walnut Formation. There be other
it
nii
undiscovered populations south of the Brazos River and on other formations.
While much of North Central Texas geology is limestone or chalk, the extensive glades of the Walnut
Formation are structurally and floristically unique to the region. Over a century ago William Bray, an early
Texas plant ecologist, stated, “before the flora of Texas suffers further radical changes, the schools of the state
by
ought to cooperate in securing a complete and authentic list of species represented carefully collected and
urban
well-preserved specimens” (Bray 1906). Since then, Texas has witnessed accelerated development, yet
we lack basic knowledge of the state’s natural history. This vascular flora of the North Central Texas Wal-
still
and an
nut Formation combines the goals of securing vouchered specimens generating ecologically relevant
circumscription of a floristic area.
This project had three objectives: Collect, identify, and archive specimens of the vascular plants found
1)
(McGowen
on the northern portion of the Walnut Formation as mapped by the Geologic Atlas of Texas et al.
and including major plant associations with
1987, 1991); 2) List all species delineate their preferred habitats,
relevant geological, pedological, and hydrological data; and 3) Analyze the flora for rare, endemic, invading,
and
disjunct taxa.
Geographical Context
Names among and ecoregions
different treatments designating physiographic regions, vegetation areas, dif-
thus the area covered by this flora has been included in different geographic contexts which are reviewed
fer;
running
Four currently recognized ecoregions dominate North Central Texas north of the Brazos River:
west to east, the West Cross Timbers, Fort Worth or Grand Prairie, East Cross Timbers, and Blackland Prairie
(Fig. In his monograph on Texas vegetation east of the 98th parallel, Tharp (1926) did not distinguish the
1).
better-known Blackland Prairie, which begins near Dallas, from the Grand Prairie; however. Hill (1901) de-
key between two The Grand much and has more angular
scribed differences the prairies. Prairie is flatter
scarps than the gentle rolling plains of the Blackland Shallower and bedrock of erosion-resistant
Prairie. soils
limestone strata alternating with softer sediments distinguish the Grand Prairie, which is recognized by the
name
“hard lime rock region,” where limestone-topped cuestas and mesas are part of the landscape (Hill 1901).
The Blackland Prairie is underlain by chalk and shale, which weather deeply to form characteristic black, cal-
heavy The dominated by An-
careous, clay soils (Diggs et 1999). Blackland Prairie a true tallgrass prairie
al. is
dropogon gerardii, Panicum virgatum, Schizachyrium scoparium, Sorghastrum nutans, and Tripsacum dactyloides,
with wildflowers and occasional mottes. Only the Austin Chalk Formation capable of forming escarpments
is
new
with
in the Blackland Prairie region (Diggs et al. 1999, Hill 1901). The fertile, rich, deep clays, combined
1800s,
plowing technologies, allowed cotton farming to proliferate in the Blackland Prairie during the late
much
destroying of the native tallgrass prairie (Diggs
et 1999).
al.
as a
with keen subprovince
Hill, a geologist a eye for landforms, defined the Grand Prairie physiographic
“northern continuation of the Edwards Plateau” This subprovince extends from the Red River to the
(1901).
Colorado River, bounded on the east by the Eastern Cross Timbers and, farther south, by the Balcones Fault
zone. “The northern and irregular western borders of the Grand Prairie terminate in the low inward-facing
escarpment which overlooks the valley of the Western Cross Timbers” This escarpment in-
(Hill 1901).
. . .
many Walnut of
cludes of the Formation outcrops north two subdivisions
of the Brazos recognized
River. Hill
the main body of the Texas Grand Prairie: Fort Worth Type Prairie and ampasas Cut Plain.
I
The Lampasas Cut was numerous low buttes
Plain described as “plains more scarped and dissected into
and mesas” (Hill 1901), starting south of the Trinity River in Parker County along the western edge of the
in
Grand Prairie and increasing in width south of the Brazos River. This includes most of the Walnut outcrops
andJohnson
Parker counties.
Worth Hill
Hill’s Fort Type Prairies extend north and east of the Lampasas Cut Plain to the Red River.
727
728 Journal of the Botanical Research
Institute of
Texas
6(2)
described two subdivisions of Fort Worth Type Prairies north of the Brazos River, aligned approximately
par-
allel between the two Cross Timbers. The Gainesville Prairie is to the east, and the ‘true’ Fort Worth
Prairie
is
on the west in Tarrant, Denton, Wise, and Cooke counties. Thus, within the area of this flora, the northern
Walnut outcrops are within Hill’s Fort Worth Prairie, while the southern are included within the northward
attenuation of Lampasas Cut
Hill’s Plain.
Worth
Dyksterhuis defined the Fort Prairie as “the northern portion of the physiographic unit known
as
Grand and mapped
the Prairie” (1946), it to cover all of Hill’s province north of the Brazos River Valley, includ-
ing areas of Parker, Hood, and Johnson counties that Hill considered Lampasas Cut Plain. Diggs
et al. (1999)
subdivided the Grand Prairie vegetational region into the Fort Worth Prairie north of the Brazos, as Dykster-
huis had, with the Lampasas Cut Plain to the south. In these maps, the area of this flora lies in the western edge
Worth
of the Fort
Prairie.
Names map
are different in the Ecoregions Texas which shows two
of (Griffiths et al. 2004), hierarchical
classification levels. At Level Texas Blackland Prairies are distinguished from Cross Timbers. Within
III, the
Cross Timbers Ecoregion, Level IV ecoregions are Eastern Cross Timbers, Western Cross Timbers, Grand
Prairie, and Limestone Cut Plain. The Grand Prairie Ecoregion between the East and West Cross
is timbers,
extending from the Red River south to the Brazos Valley, corresponding to the Fort Worth Prairie as defined by
Dyksterhuis (1946). Using the Environmental Protections Agency Level IV map, the area of along
this flora is
the western boundary of the Grand Prairie, with outliers in the nearby Western Cross Timbers.
The Worth
Fort
Prairie is described as a grassland historically devoid of trees except in waterways (Diggs
et al. 1999; Dyksterhuis 1946). Dyksterhuis sampling between 1939 and found
(1946), 1944, that Nassella leu-
had common
cotricha the greatest coverage. Other perennial grasses were Aristida spp., Bothriochloa laguroi-
des, Bouteloua curtipendula, Buchloe dactyloides, Schizachyrium scoparium, and Sporobolus compositus. Among
these, only Schizachyrium scoparium is considered typical of tallgrass prairie, and Dyksterhuis proposed that
abundance was
its relative negatively correlated with grazing disturbance Dyksterhuis emphasized
(1946).
abundance
that “the of annuals is regarded as a most significant feature” of the Fort Worth Prairie, comprising
20% Common
about
of the vegetation
(1946). annuals included cool season species such as Bromusjaponicus,
Hordeum and
pusillum, Plantago spp., together with such warm season species as Gutierrezia dracunculoides
and
Sporobolus Grand
vaginiflorus. In the Prairie Ecoregion description, Sorghastrum nutans and Andropogon
gerardii are included as representative grasses (Griffiths et 2004), though Dyksterhuis (1946) indicated they
al.
were seldom dominant
except in “relict” sites protected from grazing.
The
upland Worth
soils of the Fort Prairie from They mapped calcareous
differ typical prairie are as
soils.
and
mollisols, inceptisols, entisols (Ressel 1981). Immature and parent mate-
soils overlie the limestone clayey
showing weakly
rial, developed horizons with h gh and organic
concentrations of calcium carbonate,
i clay,
matter (Dyksterhuis The
1946). xeric aspects of the Fort Worth Prairie are due to the structure of shallow cal-
which
careous
soils, retain limited moisture. much support
Hill (1887) hypothesized that they have too lime to
The
tree growth. shallow and hard make
soils limestone
tilling impossible, and thus have encouraged cattle
grazing primary
as the land use (Diggs and
et al. 1999; Dyksterhuis 1946; Hill 1901). Today grazing pressure
suppression have had
fire the greatest impact on the Fort Worth promoting weedy species introduced
Prairie,
and
for forage species that can withstand
grazing, and encouraging woody were not pres-
invasive species that
ent 60 years ago (Diggs
et al. 1999; Dyksterhuis 1946).
The Western
Cross Timbers
border
the western edge of the Fort Worth Often the boundary oc-
Prairie.
curs where the Walnut Formation
abuts deep, and Antlers
non-calcareous, sandy from Paluxy
derived
soils
The
Formations. Western
Cross Timbers
are strips of woodlands and with occasional
savannas, intermixed
openings
prairie (Francaviglia
2000; Harris 2008; Kendall 1845; Tharp The arenaceous and siliceous,
1939).
mildly acidic alfisols of the Western Cross Timbers which
tree
create a matrix with adequate water storage,
roots can penetrate deeply
(Dyksterhuis
1948; Harris 2008; Hill 1887; Sims and Risser 2000). Quercus stellata
and
(post oak) Quercus marilandica
(blackjack oak) are the dominant with elms, hackber-
interspersed
trees,
and
ries, greenbriars (Dyksterhuis
1948; Harris 2008; Hill 1887; Kendall 1845; Tharp 1939). Washington Ir-
ving
(1985) described these woodlands
as The adapta-
“forests of cast iron” due and
their hardiness density.
Swadekand Burgess, Flora of the North Central Texas Walnut
729
and
tions of post blackjack oaks to moderate drought allow them to expand further westward than most other
trees of the Eastern deciduous forest (Tharp 1939).
As noted above, the northern boundary of the Lampasas Cut Plain has differed tremendously over the
last
Gould
century (Diggs et al. 1999; 1960; Griffith et al. 2004; Hill 1901). In the Lampasas Cut Plain, Hill de-
most
scribed the representative portion of the Walnut Formation, the Walnut Prairie; where the strata are more
exposed McGowen
extensively (Griffith et al. 2004; Hill 1901; et al. 1987). In this region, Walnut geology sup-
on
more
ports prairies valley floors instead of xeric uplands as in the Fort Worth Kendall
Prairie. (1845) also
noted a difference in the landscape as he crossed north of the Brazos River during his expedition. In the Lam-
pasas Cut Plain, the Edwards Limestone outcrops more frequently as hard, resistant caps on the mesas and
buttes. Southward, the Lampasas Cut Plain and Edwards Limestone are less dissected, forming the beginning
Edwards
of the Plateau.
Walnut
Geology of the Formation
The Walnut Formation, underlying the western edge of the Fort Worth Prairie and parts of the Lampasas Cut
exposed
Plain, is in at least 18 counties in Texas, mostly south of the Brazos River (Sellards et al. 1932; United
States Geological Survey 2010). Mapped as Walnut Clay, part of the Lower Cretaceous Fredericksburg
is
it
Group, which formed during the Comanchean period 103 million years ago (McGowen et 1987, 1991). The
al.
Walnut Formation is largely composed of limestone and less consolidated strata variously termed marl, calcar-
thinning inland north and west (Sellers et al. 1932; Scott et al. 2003). The Walnut Formation is thicker and
more exposed farther south, eventually thinning again at the base of the Edwards Plateau (McGowen et
al.
1987, 1991).
By nomenclatural convention, the Walnut Formation overlies the Paluxy Sandstone south of Decatur,
Texas; whereas north, the Antlers Formation beneath. The Glen Rose Formation defines the separation be-
is
tween the Paluxy and Twin Mountains Formations; however, the Glen Rose Formation is absent north of De-
(McGowan
catur, forcing the combination of Paluxy and Twin Mountains into the Antlers Sands et 1987;
al.
McGowen
et 1991). For the remainder of Texas, the Glen Rose Limestone is the underlying formation in-
al.
stead of the Paluxy and Antlers sandstones This has been described as an unconformity because “the
(Fig.
2).
Paluxy was deposited in a regressive sea, which readvanced over the land, depositing the Walnut Formation”
(Sellards
etal. 1932).
The Goodland Limestone the Walnut Formation in Parker and Tarrant counties and is undiffer-
overlies
entiated from the Walnut on geologic maps in Wise and Montague counties, making outcrops harder to locate.
Goodland Limestone can be distinguished from Walnut Limestone by its nodular fabric, paler whitish color,
and decreased abundance of Texigryphaea In Hood,Johnson, and Somervell counties, nearer the Brazos
fossils.
River, the Goodland thi™ Walnut expands, and Comanche Peak and Edwards limestones are exposed as
the
The
the overlying The boundary between Goodland and Walnut Formations is not clearly defined.
formations.
County been southward
lower Marys Creek Member Goodland Formation in Tarrant has traced to
of the
match the upper marl Walnut Formation beneath the Comanche Peak Formation, leading to the
interval of the
Goodland
Marys Creek Marl be considered part of the
Proposal that north of the Parker-Hood County line the
The Walnut Formation
Formation; whereas the south within the Walnut (Scott et al. 2003). is also
to is
it
known and West where
in Oklahoma, where with Goodland Limestone (Hill 1901), in Texas, it
associated
is
it
on Double Mountain in Stonewall
is largely associated with the Edwards and Comanche Peak formations, as
County
(Eifler 1993).
making up
and nonchalky limestones the base of the
Hill (1901) described the Walnut Formation as clay
on
laminated weathering yellow oxi-
Fredericksburg of calcareous clays,
Division, consisting of “alternations
weather black
dation, and agglomerate. In places they into rich soils
semicrystalline limestone shell ...
flags,
and make many Walnut Limestone strata are
In the area of this flora,
extensive agricultural belts” (Hill 1901).
which
ca dominated by Texigryphaea, are relict
sily agglomerates fossil
recognizable
as coquinites or shell
aorm and Marls
and weather cream to yellow olive in flaggy layers.
beds. Fresh exposures are blue in color
730 Journal of the Botanical Research
Institute of Texas
6(2)
between limestone layers vary in thickness and are easily penetrated by The base of the Walnut consists
roots.
of calcareous clays intercalated with cemented limestone The Goodland, Comanche Peak, and
(Hill 1901).
Edwards
formations and
are paler chalkier than the yellows and browns Walnut Formation, helping to
of the
them
distinguish
visually (Hill 1901).
The Walnut Formation developed through marine sedimentation in the Lower Cretaceous when the Gulf
Mexico
of spread inland, covering Texas. The Lower Cretaceous formations tend to be some of the largest re-
gional formations, extending from mountainous
boundaries in Oklahoma Mexico. Deposited along belts
to
through marine
influence, the harder limestones alternate with clay and overlie sands, creating dip and cut
plains as well as low escarpments carved by erosion (Hill 1901). To the younger geological layers are en-
east,
on
countered
top of the Walnut, dipping
eastward. These until
layers are eroded into gentle east-facing slopes,
a resistant limestone layer is exposed. Here a steep, west-facing slope formed by rapid erosion of a less resis-
is
below
tant layer the harder
cap, creating a cuesta topography with and steep west-
gentle plains sloping east
facing escarpments. The make
limestone
layers erosion resistant shelves connected by erodible slope-forming
marl layers (Diggs
et 1999; Dyksterhuis
al. 1946; Hill 1901).
The Walnut
Formation is unique in the contrasting lithification of which creates the diversity of
its strata,
modern
habitats. There are deep clays, hard limestone and from marls
glades, shallow barrens derived
soils
and
fossil shell fragments. Seeps are also abundant on barrens and and with the un-
slopes, they often interact
derlying sands. Slope seeps
frequently occur where water and meets less
flows through fractured limestone
permeable
clay or weathered
less massive water to
limestone
layers, creating a perched water causing
table,
flow and emerge
laterally, as a seep where the stratum is exposed (Burgess and Busbey 2010, Llado 2011) (Fig-
Quaternary
2). alluvial deposits over Paluxy Sandstone make up the bulk of parent materials in river val-
soil
leys adjacent to upland Walnut exposures McGowen
McGowen
(Eifler 1993;
1991).
et al. 1987; et al.
Swadek and Burgess, Flora of the North Central Texas Walnut
Description
Site
and
Brazos
The Red, Trinity, rivers are the principle waterways, excluding lakes, that cross through the Walnut
The
Formation. Brazos is the southern boundary for the study site and the Red River the northern boundary.
and
Several tributaries headwater streams of the Trinity River run through the northern part of the Walnut
exposures within the study area. For this research, the targeted area of the Walnut Formation between ap-
lies
W
proximately 32.25° and 34°N and -97.25° and -98° within the study area. The Walnut Formation extends
much west and south beyond
farther the borders of the study
site (Fig.
1).
The area and elevation range of the Walnut Formation is difficult to calculate, as these data are not typical
in geologic maps, and have not been found in any geological literature. Based on estimates, the area equates to
km
(McGowen
around 390 sq et 1987). The elevation of collected vouchers ranges from a low of about 225
al.
m
m
County
in Tarrant to a high of 435 in Parker County.
cm
Tarrant County receives an average of 86 of rainfall per year decreasing to the west and increasing to
&
the east. The first freeze occurs around November 17 each year and the last freeze around March 15 (Alvarez
Plocheck yielding an average growing season of 249 days (National Oceanic and Atmospheric Adminis-
2011),
tration 2012). The climate described as humid subtropical with hot summers, having annually wide tem-
is
perature variations and mild winters (National Oceanic and Atmospheric Administration 2012). The rainfall
and temperature patterns during the duration of this study, yielded lower than normal rainfall, 51 to 56 cm,
KNFW
and 2011 was one of the hottest summers on record based on data from the weather station in south-
Worth
west Fort (National Climatic Data Center 2012).
METHODS
Vascular plants were collected on the Walnut Formation north of the Brazos River from January 2010 to June
2012, both on the formation and on slopes below Walnut outcrops, where colluvial deposits of marl and co-
quinite cover Paluxy and Antlers sands. Here the calcareous sediments interact with the sand, extending the
range of the prairie limestone flora downslope into the Western Cross Timbers.
Maps from The Geologic Atlas Texas identified approximate boundaries of the Walnut Formation. Mc-
of
Hood
Gowen and
et al. (1987) covers the area north of the Brazos River in Parker, Tarrant, Johnson, counties.
McGowen Goodland and Walnut
et (1991) covers Wise and Montague counties directly north; however, the
al.
Hood
formations are undivided on map. Tarrant, Parker, Wise, Johnson, and counties contained the study
this
sites, as no significant outcrops were known from Montague County.
Walnut maps and the presence of distinctive massive
Formation outcrops were verified using geologic
limestone strata with abundant Texigryphaea. First, potential sites were located using geologic maps, then
spanned broad north-south gradient, fewer private
publicly accessible areas were located. Since public parks a
lands were surveyed. GIS maps were created showing the Walnut Formation overlaid with county streets to
Walnut
target Outcrops.
stretches of road with high percentages of
&
method (Hartman Nelson
“meander
Voucher herbarium specimens were collected using the search”
was photographic voucher was taken to help
2008), in when only one plant present, a
triplicate - possible. If
&
Preserve the population. Specimens were identified using Skinners Mahler’s Illustrated Flora of North Central
and
North America recent publications
Texas nomenclature. Flora
(Diggs which of
the basis for
et al. 1999), is
&
were Nesom Smith 2003) for identifications of species
also used Small Kiger 2004; 2006; et al.
(Estes 2007;
uamed were confirmed with herbarium specimens at the
or discovered in the area since 1999. Identifications
and
Bob O’Kennon, Barney Lipscomb,
Botanical Research Texas (BRIT). Experts consulted include
Institute of
Amanda type, habitat description, associated plants, species
Neill (BRIT). Specimen data include the date, soil
abundance, and GPS coordinates. References to protocol include
images of the plant and habitat, locality,
its
and Wilson Data and images were
Davis and (2000). field
Neill
(1961), Diggs Jennings et (2009),
et al. (1999), al.
imported an online biodiversity information system for public
into Atrium (BRIT Herbarium 2012),
Digital
TEX/LL and TAES. The
were shared with
access. Specimens BRIT Herbarium. Duplicates
were archived in the
Fmt TAES.
Worth Nature Center and Refuge received the duplicates of specimens collected there, instead of
732
made
There were 835 collections from the North Central Texas Walnut Formation by the authors. The
BRIT Herbarium was consulted for other collections not included in the 835; thus all specimens cited are de-
posited at BRIT. The authors did not personally verify the exposed geologic stratum for all specimens collected
by other botanists unless they were from specific sites or collecting events. Legacy collections, from BRIT, were
included due to their presence on the Walnut Formation based on GPS coordinates and associated plant spe-
m
GPS
Goodland Limestone was mapped within 200 of the plants location, the stratum the specimen
cies. If
was found upon was questionable and the collection omitted from the checklist.
A
full checklist of the flora was created, and the flora was analyzed for rare or endemic taxa, invasive or
common
potentially invasive species, and disjunct taxa. Releve plots were completed for plant communities
to
the Walnut Formation. Sites were subjectively selected based on local knowledge of representative sites and
Random was was homogenous and
availability. site selection avoided, as the objective to define repetitive plant
communities in similar topographic, geological, and pedological contexts. This was done to confirm plant as-
sociations within and across geological formations, and to facilitate future comparisons (Jennings et al. 2004).
Plots ranged in size and edges were avoided to reduce variability and to ensure the similarity of communities.
GPS
Data collected for each plot includes location, exposed geologic stratum, hydrologic regime, slope,
soil,
aspect, topographic position, percent cover and height class for each plant species present, and percent cover
and
of non-vascular species abiotic factors.
Plant communities were described as in Jennings et (2009). Associations are named using dominant
al.
and
diagnostic taxa for each community. Taxa found within the same stratum are indicated by a hyphen, in
by and The
different strata a slash, parenthetic notations indicate lower constancy or confidence. order of spe-
cies names indicates decreasing dominance (Jennings e 2009). No formal quantitative analysis on the
t al.
was
releve data done; these associations are based largely on observation and constancy of dominant and diag-
The many
nostic species. authors believe of the following communities are widespread enough to warrant
tentative recognition in the Association Records database (NatureServe 2012b).
AND
RESULTS
DISCUSSION
Results of the study are included in the following Major Comparison with the
sections: vegetational habitats,
Walnut Formation South of the Brazos River; Unique Comparisons; Range Extensions, Invad-
Sites; Floristic
Endemic and Summary
Taxa;
ers, of Taxa.
MAJOR VEGETATIONAL
HABITATS
may
While communities
plant not be mappable units as defined by the Ecological Society of America Vegeta-
tion Classification Panel (2011), these provisionally named were consistently
associations are patterns that
encountered throughout North
the Central Texas Walnut Formation and could be studied further for consid-
Plant communities aligned almost perfectly with and depth and
geological pedological boundaries. Soil
type were best indicated by vegetation structure and cover. As soil depth decreased, there was a strong correla-
tion with light intensity as the canopy cover decreased (Fig. The exception weathered limestone with
3). is
pockets of soil accumulation in deep crevices, allowing trees to take root and create a shady canopy as in a
limestone scrub woodland.
While Worth
the Fort was mixed
Prairie a grass and overgrazing
prairie in the 1940s, suppression
fire
&
&
converted to a savannah (Fuhlendorf Engle Mayer dominate with
it 2004; Khalyani Shorter grasses
2011).
decreasing soil depth. There are surges of annuals Within
in the spring and coinciding with seasonal rains.
fall
the herb stratum, perennial forbs, annuals, and perennial
succulents dominate herbaceous
the spring, while
bunchgrasses dominate
the
fall.
Due
and
to the structural similarity of these habitats with Kentucky,
limestone cedar glades in Alabama,
we
Tennessee, follow the habitat designations described by Baskin and Baskin 2003) and Quarterman
(1996,
(1950a, 1950b, 1989). Glades are open areas of exposed Walnut Limestone with 0 5 cm Here soil forms
to soil.
primarily in limestone cracks yielding patchy though some
vegetation,
typically less than 50 percent cover;

734 Journal of the Botanical Research Institute of Texas
6(2)
Our from
terminology limestone cedar
form the erosion-resistant scarps or glade habitats. differs glade habi-
in the southern Appalachians in that we use the term “Walnut Limestone Glade,” though this is somewhat
tats
misnomer because walnut do not dominate them as cedars do in the southeast; rather the Walnut Lime-
a trees
name no
having
stone the geological stratum of the these habitats, the formation relation to the dominant
is
plants.
n Walnut
and landscape the Formation. Glades
Glades are characteristic feature; ai
isive
ai
cm
und
areas of exposed limestone outcrops and rocky areas with soils a 0 to 5 deep. Texigryphae;
shell fragments usually dominate surfaces. The most common soils in Hood, Parker, and
Greenwade
clayey upland paralithic entisols in the Maloterre Series (Colburn 1978; et al. 1 7; Ressel 1981). In
Wise County, the Maloterre Series not mapped and glades are shown to be associated v
is
Venus Series, both mollisols (Ressel 1989), which, following field investigations, do not appear to be present on
glades. The soils associated with glades in Wise County are very gravelly, shallow, undeveloped soils over
limestone. They have no mollic epipedon and are likely entisols.
Glades are frequently found on ridge tops at the LBJ National Grasslands. Elsewhere glades are found next
hillslopes. During storm events, impermeable limestone provides little to no infiltration of runoff, creating
development
what arguably infiltration excess (Hortonian) overland flow, thus preventing or slowing soil
is
Thus, glades are free of trees, except for occasional mottes, and shallow soils are incapable of retaining
much
water, thus plants are often succulent or extremely shallow rooted. Deep-rooted perennials establish
their roots in limestone cracks; some probably extend roots to the marl, which has greater water holding poten-
The
Glades are dominated by gravel or open usually with than 50 percent herbaceous coverage.
tial. soil, less
glades are a distinct habitat of specialized, often endemic plants. Few plants are weedy or characteristic of ru-
purpurea Lime-
Aristida v
)
where
glade seeps the s well dra
5
and
cognata, Erioneuron pilosum, Tridens muticus. Limnodea arkansa
warm Other
cool season annual grasses, while Sporobolus ozarkanus the dominant season annual grass.
is
common
components of dry glades include perennial herbaceous dicots such as Dalea reverchonii, D. tenuis,
includ-
Grindelia lanceolata, Lesquerella engelmannii. Paronychia virginica, Sida abutifolia, scattered succulents
ing Coryphantha sulcata, Escobaria missouriensis, E. vivipara, Opuntia phaeacantha, and Talinum calcaricum.
Bouteloua curtipendula, Prunus rivularis, and Schizachyrium scoparium can be found in deep limestone
crevices or on glade edges where the hillslope begins. As the glade thins, at the edge of the hillslope, the vegeta-
The
tion thickens. species listed above are present in greater densities and Asclepias asperula, Artemisia ludovi-
and may
ciana, Bouteloua curtipendula, Liatris mucronata become dominant.
Dalea rexerchonii—Talinum calcaricum—Minuartia michauxii Limestone Glade Herbaceous Vegeta-
—
on
tion Association. In less disturbed sites, this association occurs where has been thinned by erosion
soil
the upslope side of a limestone expanse, or where shallow on downslope side
soil has started to accumulate the
may
and
of a glade. This interesting glade association is not locally extensive, but widespread among glades
is
it
be more appropriately called a sub-association; however, when and recog-
present the association distinctive
is
nizable on extremely shallow, clayey soils bordering expanses commune, Sedum nut-
of bare limestone. Nostoc
and common
tallianum, Sporobolus ozarkanus are very in these
associations.
Glades are often surrounded by barrens or areas of 5-25 cm with small patches
locally thin soils, at least deep,
of exposed bedrock, rock fragments, and cryptogamic crusts. Barrens may be on benches where there is
also
more topographic relief; often they are interspersed with seeps. Dominated by bunch grasses, Schizachyrium