Appendices & Glossary - Botanical Research Institute of Texas

1204 APPENDIX TEN/EAST TEXAS AS A UNIQUE HABITAT
royal fern. In presettlement times, even small areas of prairie were probably close by—based on early
explorer accounts (e.g., Lincecum 1835), there were numerous, scattered, small prairies at various
places in the Pineywoods. Names given by early settlers to at least 46 places in the forested area of East
Texas also confirm the presence of prairie—e.g., Mustang Prairie at Crockett, Tarrkington Prairie in Liberty
County, and Shawnee Prairie in Angelina County (Truett & Lay 1984).
3) Similarities to the tropics—Another particularly striking aspect of East Texas, particularly the Big
Thicket, is its resemblance in a number of respects to tropical rain forests. Similarities include the very
tall trees well over 100 feet in height, the swollen buttressed bases on bald cypresses and water tupelos,
the presence of epiphytes (e.g., Spanish moss, resurrection fern), numerous evergreen species (e.g.,
southern magnolia, sweetleaf, wax myrtle, red bay, cherry laurel, American and other holly species,
smilax species, etc.), high species richness (discussed above), abundant individuals of the palm family
(Sabal minor, dwarf palmetto, sometimes dominating the forest floor—e.g., palmetto-hardwood flats),
abundant Orchidaceae (45 orchid species), numerous and often conspicuous ferns and fern allies (74
species) (Diggs et al. this volume), bamboo (Arundinaria gigantea, giant cane, historically forming
large cane brakes), areas with standing water for long periods of time (e.g., Neuces River bottoms),
abundant lianas (= large woody vines) extending high into the canopy, the presence of leaf-cutter ants,
and even (until the early 1900s) jaguars (Bailey 1905). In addition, there are numerous representatives
of many characteristically tropical families such as Annonaceae (including pawpaw), Araliaceae
(hercules’-club), Bignoniaceae (crossvine), Lauraceae (red bay), Marantaceae (powdery thalia),
Mayacaceae (bog-moss), Melastomataceae (meadow beauty), Menispermaceae (moonseed), and
Symplocaceae (sweet-leaf).
4) Influence of glaciation—During the Quaternary Period (beginning ca. 1.8 million years ago and
including the Pleistocene and Recent epochs), there have been profound changes in the vegetation of
the southeastern U.S. including East Texas. During the Pleistocene Epoch (“ice ages”), there was significant
climatic variability and at least 20 glacial-interglacial cycles. Not surprisingly, widespread
changes in vegetation were associated with these climatic fluctuations (Delcourt & Delcourt 1993).
During the last major period of full glaciation (80,000 to about 18,000 years ago), vegetation of the
eastern U.S. was radically different than at present. Sea level was 100 to 120 meters lower than during
modern times and the Laurentide Ice Sheet extended south to approximately 40° N latitude (near the
junction of the Ohio and Mississippi rivers). Boreal forest could be found south to ca. 34° N latitude,
and between 34° and 33° N latitude existed a narrow ecotone between “northern boreal and more
southern temperate communities” (Delcourt & Delcourt 1993). In this regard, it should be noted that
the zone between 34° and 33° latitude cuts across the northern several tiers of East Texas counties (e.g.,
Bowie, Grayson, Hunt, Red River). “South of latitude 33°, across the southern Atlantic and Gulf coastal
plains, floristic elements of temperate deciduous forest occurred with plant taxa characteristic today
of southeastern evergreen forests” (Delcourt & Delcourt 1993). Thus, it was in areas such as East Texas
that some eastern deciduous forest species found refuge during full glacial times. Indeed, data from
East Texas bogs (e.g., Boriack Bog, Lee Co.) in the Post Oak Savannah confirms the presence of such deciduous
forest genera as Acer, Alnus, Carya, Castanea, Cornus, Corylus, Fraxinus, Myrica, Quercus,
and Tilia more than 15,000 years ago, and suggests the region was heavily forested near the end of the
last glaciation (Bryant 1977; Bryant & Holloway 1985b). While most of these genera can still be found
in East Texas today (generally farther east), the profound climatic differences at that time are reflected
in the presence of small amounts of Picea glauca (white spruce) pollen in late glacial deposits at
Boriack Bog (radiocarbon dated as older than 15,000 years before the present) (Bryant 1977; Holloway
& Bryant 1984; Bryant & Holloway 1985b). This cold loving species occurs today only much farther
north. Bryant and Holloway (1985b) concluded that as post-glacial warming occurred in East Texas,
the glacial age deciduous forest “lost certain key taxa such as Picea and Corylus yet the region remained
forested with a wide variety of deciduous tree taxa.” In other words, at 15,000 years before
present, the mean annual air temperature was 5° C less than at present, conditions were moister, and
there was a more widespread forest mosaic over most of Texas (Bryant 1977; Stahle & Cleaveland 1995).
Subsequently, there has been in general a warming and drying trend in Texas (Bryant & Holloway
1985b) with consequent effects on the vegetation.