ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...

Forests define East Texas, and to a great extent they always have.
— Mark Barringer, 2002
THE PINEYWOODS
CONTRIBUTED BY JAMES VAN KLEY (PAGES 76-106)
DEPARTMENT OF BIOLOGY, STEPHEN F. A USTIN STATE UNIVERSITY
NACOGDOCHES, TX 75962
OCCURRENCE OF THE PINEYWOODS
The Pineywoods vegetational area (Figs. 41, 42) forms the eastern edge of Texas. It occupies
an area of about 63,200 square kilometers (6.3 million hectares or 24,400 square miles),
about 9% of Texas, and extends roughly from Bowie County in the north to Orange and
Hardin counties in the south. Upshur, Smith, Anderson, Houston, Walker, and Montgomery
counties (north to south) form the approximate western boundary (Hatch et. al 1990),
much of which corresponds with the 98 cm (40 inches) mean annual precipitation line
(Larkin & Bomar 1983). Topographically, the area ranges from nearly flat to gently rolling
or hilly and varies in elevation from about 150 m (500 feet) above sea level in the north and
west to only slightly above sea level at the southern margin in the lower part of the Big
Thicket. The Pineywoods represents the western terminus of the pine and deciduous forests
of the southeastern coastal plain, which extends from Virginia to Texas (Christensen 2000;
Delcourt & Delcourt 2000). Floristically and ecologically, the area has more in common
with Louisiana and other southeastern states than it does with the remainder of Texas. Braun
(1950) divided the southeastern coastal plain into an oak-pine forest region, which in East
Texas mainly occurs to the north of Nacogdoches County and to the west of the Trinity River,
and the southeastern evergreen forest which occupies the remaining southeastern portion of the
Pineywoods. The ecological classification system used by the U.S. Forest Service (Keys et al.
1995; Turner et al. 1999) likewise divides the Pineywoods into two Provinces: the Southeastern
Mixed Forest Province and the Outer Coastal Plain Mixed Forest Province. A chief
difference is that longleaf pine (Pinus palustris) dominated many uplands on the Outer
Coastal Plain Mixed Forest Province prior to European settlement, whereas the region to the
north and west was outside of this range and its upland presettlement forests consisted of a
mixture of shortleaf pine (P. echinata) and deciduous hardwoods (Cruikshank & Eldredge
1939; Evans 1997). MacRoberts et al. (2003a) provide a similar delineation. Human activity
over the past two centuries has radically altered the region’s vegetation, and many formerly
extensive natural ecosystem types are rare on the modern landscape. Many of the best
remnants are threatened by human activity and time is running out to preserve them.
Within the Pineywoods are two long-famous areas, the Caddo Lake ecosystem in the northeast
and the Big Thicket in the southeast—both of these are discussed in more detail
beginning on page 149 and page 156, respectively.
GEOLOGY OF THE PINEYWOODS
At the beginning of the Tertiary Period (65 million years ago), the area now occupied by the
Pineywoods was covered by a shallow sea, an expanded Gulf of Mexico (Spearing 1991).
The Gulf gradually retreated southeastward, and eastern Texas was built up as a series of
east-west oriented bands of sedimentary deposits (Dumble 1918). As one travels from the
northern Pineywoods southward toward the Gulf of Mexico, surface layers become
progressively younger and the landscape shows progressively less topographic relief
(Bernard & LeBlanc 1965).
These deposits are variously of marine and continental origin, the result of multiple
advances and retreats of the Gulf over the ages (Sellards et al. 1932). The northern portion
is mainly of Eocene age (54–38 million years old) and is composed largely of sands