PHYTOGEOGRAPHY OF THE BIG THICKET, EAST TEXAS

2007·4.4 MB·English

by  Michael H Macroberts

PHYTOGEOGRAPHY OF THE THICKET, EAST TEXAS
BIG
MacRoberts and MacRoberts
Michael Barbara
H.
R.
Bog
Research
740 Columbia^ Shreveport, Louisiana 71104, U.S.A.
and
Museum
l-lerbarium, of Life Sciences
Louisiana State University in Slireveport, Slireveport, Louisiana, 71 U.S.A.
15,
1
ABSTRACT
We We
examined the floristic relationship between the Big Thicket of east Texas and the remainder of North America. found that floristi-
cally the Big Thicket overwhelmingly eastern and notably southeastern. There very western influence on
is is little
it.
RESUMEN
Hemos Hemos
examinado las relaciones floristicas entre el Big Thicket del este de Texas y el resto de Norte America. encontrado que
florlsticamente el Big Thicket es sorprendentemente oriental y notablemente del sureste. Hay muy poca influencia occidental en el.
INTRODUCTION
made
Extraordinary claims have been regarding the ecology of the Big Thicket of east Texas. has been
It
described as exceptionally species rich, unusually diverse in plant communities, and a biological "crossroads"
&
between eastern and western floras (see Cozine 2004; MacRoberts MacRoberts 2004; Diggs et al. 2006
On
for reviews and literature). the other hand, recent examinations of these claims have led to the conclu-
sion that the Big Thicket is not a crossroads but is southeastern with levels of habitat diversity and species
&
richness comparable to other areas of the southeast (MacRoberts MacRoberts 2004; Diggs et 2006;
al.
MacRoberts 2007). As Diggs (2006:166) conclude "these conflicting views need examination."
et al. et al.
However, such an examination has been hampered by a lack of adequate floristic data. Until recently, the Big
now
Thicket flora has been understudied and undocumented (MacRoberts et 2002b), a problem largely
al.
overcome by inventory of the major part of the Big Thicket National Preserve (MacRoberts
a floristic et al.
Brown
2002b; et al. 2005, 2006a, 2006b, in prep.), by a reexamination of earlier plant collections from the
Big Thicket National Preserve (L.E. Brown pers. comm.; Warren Pruess pers. comm.), and by the publica-
and
tion oi Atlas of the Vascular Plants of Texas (Turner et al. 2003) Illustrated Flora of East Texas (Diggs et al.
much now
2006). Additionally, better distribution information on the flora of North America available
is
&
USDA
Meacham
North America 1993-2006).
Kartesz 1999; 2007; Flora of
(e.g.,
Figure shows the location of the Big Thicket. While the exact geographic boundaries of the Big
1
Thicket are ill-defined, it is generally considered to consist at least of Newton, Jasper, Hardin, Tyler, Polk,
and northern Liberty county, or an area of approximately 13,500 square kilometers (see Diggs et [2006]
al.
and Within
for a discussion of the Big Thicket location a description of its ecology). this area is located the
Big Thicket National Preserve, with 12 units ranging from 222 ha to 10,100 ha and totaling about 34,000 ha.
Since the units were originally selected to represent the Big Thicket community structure and flora (Peacock
1994; Cozine 2004; Diggs et al. 2006), a floristic inventory of the units should constitute a fair sample of
the area.
As part of a continuing study of the flora of the West Gulf Coastal Plain, in this paper we examine the
relationship between the Big Thicket and the remainder of North America north of Mexico.
floristic
METHODS
Brown
Using the vouchered of MacRoberts (2002b), (2005, 2006a, 2006b, in
1. floristic lists et al. et al.
Warren we
prep.), Pruess (pers. comm.), for the Big Thicket National Preserve, developed a master of the
list
-
J. Bot. Res. Inst. Texas 1(2): 1149 1155.2007
1150 Journal of the Botanical Research Institute of Texas
1(2)
Location of Big Thicket (hatched area) and Caddo Parish (stippled area).
Fig. 1
.
vascular plant species occurring in the Big Thicket region of east Texas. This consists of 1076 species.
list
Using Kartesz and Meacham (1999) and Flora North America (1993-2006), we plotted the North American
of
by and
distribution of these species province, region.
state,
2. Because Texas is a large state and because there is a major floristic ecotone across its center where
&
east and west meet (MacRoberts MacRoberts 2003; Diggs et al. 2006), we divided the state into 24 areas
km
approximately 180 on a side and using Turner et al. (2003) and Diggs et al. (2006), we plotted the dis-
tribution of the species where possible in our master (see method above) across Texas to determine the
list 1
relationship between the Big Thicket and other areas of Texas. This consists of 1035 species.
floristic list
Using Matos and Rudolph Brown Turner and Diggs
3. (1985), et al. (2002), et al. (2003) et al. (2006),
we
located species from the Big Thicket area (Newton, Jasper, Tyler, Hardin, Polk, and northern Liberty
all
We
county) not in our master (see method above). combined this with our previous making a
list 1 list list
Meacham we
sample of 1462 species. Using Kartesz and (1999) and the Flora North America (1993-2006),
of
We
determined their North American distribution. then classified all species into one of five categories: 1)
western: species that occur exclusively or predominantly in the west (the floristic divide between east and
west is about 97 or 98 west longitude [MacRoberts et al. 2003]) (e.g., Loejlingia squarrosa Nutt.), 2) central:
species that are predominantly in the central plains area (e.g., Tradescantia occidentalis (Britt.) Smyth), 3)
MacRoberts and MacRoberts, Phytogeography of the Big Thicket, East Texas 1151
Fig. 2. Distribution of Big Thicket flora as percentage of total in each state, region, or province.
universal: species that occur in virtually states and provinces in North America Athyriumjelix-femina
all (e.g.,
(L.) Roth), 4) eastern-western: species that are not universals but which occur equally in both the east and in
the west (e.g., Evolvulus sericeus Sw., Phyla nodiflora (L.) Greene), 5) eastern: species that are either exclusively
found in the east or are predominantly in the east Xyris spp.)(this category includes West Gulf Coastal
(e.g.,
Our
Plain endemics [MacRoberts 2002a]). purpose was determine the influence of different regions
et al. to
on
the flora of the Big Thicket.
Brown
Using MacRoberts 2006a, 2006b, Turner
4. et al. (2002b), et al. (2005, in prep.). et al. (2003)
and Diggs et al. (2006), we located all species from the Big Thicket area (as in method 3) that also occurred
Gameron
in south Texas (Kenedy, Brooks, Jim Hogg, Zapata, Starr, Hidalgo, Willacy, counties) and deter-
mined North American Our purpose was determine
their distribution. to the distributional characteristics
common
between and what commonality
of species in the Big Thicket outlying regions to see their was.
The two have 303 common.
areas species in
we
3. In order to develop a comparative sample, using MacRoberts and MacRoberts (2006) applied
km
methods 1 and 3 to the flora of Gaddo Parish, Louisiana. Gaddo Parish is located about 200 north of
the Big Thicket in the northwestern corner of Louisiana, in the center of the West Gulf Goastal Plain (Fig.
We
used a random sample of 417 species of the Gaddo Parish flora as in method and 1168 species as
1). 1,
method
in
3.
Exotic species are excluded from of our data
all sets.
RESULTS
Figure 2 shows the distribution of Big Thicket flora as percent of total species found in each state, province,
shows shows
or region. Figure 3 the distribution of Big Thicket flora as percentage across Texas. Table
1
1152 Journal of the Botanical Research Institute of Texas
1(2)
Fig. 3. Distribution of Big Thicket flora as percentage across Texas: West Gulf Coastal Plain outlined in dashes. Big Thicket outlined in dots.
how
North America and Caddo shows
the regions of relate to the Big Thicket Parish. Table 2 the relationship
common
between the species that occur in between the Big Thicket and south Texas. Figure 4 shows the
Caddo
distribution of Parish flora as percent of total species found in each state, province, or region.
DISCUSSION
98%
The method show
results of that the Big Thicket phytogeographically eastern; notably southeastern:
1 is
88% 48% New
of the Big Thicket flora occurs in Louisiana, 91% in Mississippi, in Florida and Georgia, in
New common
York, but only 19% in Mexico. In fact, the Big Thicket has more of its flora in with Wisconsin,
New
Michigan, Minnesota, Ontario, and England than has with any western state or province. Method
it
2, not surprisingly, shows that within Texas the Big Thicket is floristically most similar to east and central
Texas, notably to the West Gulf Coastal Plain region of which it is a part. Method 3 shows that eastern spe-
cies dominate the Big Thicket, with 81% of the total, followed by eastern-western species, with 10%, and
96%
universal species, with 5%. Western and central species account for slightly less than 4%; that over
is,
Method shows
of species are eastern associates (eastern, universal, eastern-western). 4 that, of the species
MacRoberts and MacRoberts, Phytogeography of the Big Thicket, East Texas 1153
and Caddo
Table Regional affiliation of Big Thicket Parisli flora
1
.
Caddo
Big Thicket
Parisli
Number Number
Region of Percent of of Percent of
Species Species Species Species
Western 19 17
1.3 1.4
Central 36 2.4 51 4.4
Universal 77 5.3 85 7.3
Eastern-Western 143 9.8 181 15.5
Eastern 1187 81.2 834 71.4
1462 1168
Total 100.0 100.0
common
Table 2. Regional affiliations of species in to floras of Big Thicket and south Texas.
Number
Region of species Percent of Species
Western
9 3.0
Central 12 4.0
Universal 33 10.9
Eastern-Western 102 33.7
Eastern 147 48.4
Total 303 100.0
common
in between the Big Thicket and south Texas, eastern species dominate, with 48%, followed by
93%
eastern-western species, with 34%, and universal species, with 11%; in other words, of the species are
7%
eastern associates (eastern, universal, eastern-western). Western and central species account for only of
common
the total. This last analysis also makes clear that the vast majority of species held in between such
areas as south Texas and the Big Thicket are eastern, not western, indicating that the Big Thicket not an
is
ecotone or "crossroads" between east and west but located fully in the eastern part of the North Ameri-
is
can region (Austroriparan subprovince) (McLaughlin 2007). Almost without exception western and
floral
central species that occur in the Big Thicket are very rare there and are usually associated with specialized
uncommon
and such and barrens Smith) Smith,
habitat, as prairies Croptilon rigidijolium (E.B. E.B.
(e.g.,
Hedeoma drummondii
Benth.).
The Caddo Parish analysis (method 5) reinforces this conclusion. While Caddo Parish has more in com-
mon
with states and provinces north of Arkansas, Oklahoma) than does the Big Thicket (MacRoberts
it (e.g.,
&
New New
MacRoberts 2006, unpublished has approximately the same relationship with Mexico,
data),
it
York, Mississippi and Florida as does the Big Thicket. Additionally, while Caddo Parish partakes of the same
percentage of western species as does the Big Thicket, has a higher percentage of central, universal, and
it
West
east-west species than does the Big Thicket. Clearly, therefore, the Big Thicket not exceptional in the
is
Gulf Coastal Plain in its affinities to other regions except perhaps the east and/or southeast.
What many
can be truthfully said about the Big Thicket that eastern plants reach their western and
is
Some
southern limit in that region. of these species are: Cypripedium kentuckiensis C.F. Reed, Cy villa racemijlora
Eriocaulon compressum Lam., Fagus grandijlora Ehrh., Hypericum galioides Lam., Lechea minor Leucothoe
L., L.,
racemosa (L.) Gray, Rhexia petiolata Walt., Rhododendron canescens (Michx.) Sweet, Stewartia malacodendron
Many
and Chapman.
L., Triantha racemosa (Walt.) Small, Trillium recurvatum Beck, Xyris stricta other eastern
much
species get farther west than the Big Thicket; examples include: Drosera capillaris Poir., Eriocaulon
decangulare L., Liatris pycnostachya Michx., Rhexia mariana L., Sarracenia alata Wood, and Xyris torta Sm.
Eew
truly western or central species reach the Big Thicket; western and central habitat simply not there
is
very
or limited.
is
1154 Journal of the Botanical Research Institute of Texas
1(2)
4. Distribution of Caddo Parish flora as percentage of total in each state, region, or province.
Fig.
ACKNOWLEDGMENTS
Warren Pruess provided an updated (January 20, 2007) of the plants collected from the Big Thicket
list
was by Agreement
National Preserve, a project that supported, in part, a National Park Service Cooperative
Two
(No. 14001004) Paul Harcombe, Department of Ecology and Evolutionary Biology, Rice University.
to
anonymous made
reviewers useful suggestions.
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