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

118 INTRODUCTION/VEGETATION OF POST OAK SAVANNAH
Americans were present and possibly had significant impacts on the vegetation through such
mechanisms as increased fire frequency. Holloway et al. (1987), based on pollen analysis of
Weakly Bog in Leon County, suggested that the Post Oak Savannah became established only
between 1,500 and 2,000 years ago as increasing aridity resulted in a vegetational shift from
oak woodland to savannah-like plant communities. While the pollen data may represent a
significant one-time shift in the vegetation, there have been numerous changes in vegetation
since the end of the last glaciation (Bousman 1998), and the continuing “state of flux”
(Smeins 1984) mentioned above should not be forgotten. Because of all these complexities,
the exact presettlement vegetation pattern is particularly difficult to estimate.
Animal life on the Post Oak Savannah was in general a mixture of that found on the
adjacent Blackland Prairies and Pineywoods. Since detailed discussions are given for the
Blackland Prairie and Big Thicket portion of the Pineywoods, no further discussion of presettlement
animal life is given here.
As settlers moved into the area, much of the Post Oak Savannah was rapidly converted
to cropland or pasture. In the words of David Diamond of the Texas Natural Heritage
Program (in Bartlett 1995):
The prairies are more fertile, yet initially were harder to plow because they were clay soils, and so
they were not plowed as quickly as the Post Oak Savanna. A lot of the savannas were plowed. They
grew cotton or other crops, and the soil wore out quickly because it wasn’t as fertile as the Blackland
Prairies. Later on, when the prairies were plowed, the Post Oak Savanna went back into rangeland
of some sort and today is no longer plowed.
Today, much has been cleared and large areas are occupied by economically useful exotics.
As pointed out by Simpson (1988), it is “used largely for ‘improved’ pasture, with vast
acreages sodded to Bermuda Grass and seeded to Bahia Grass.” On the other hand, large
expanses of once-cleared land are now in second, third, or fourth growth woody vegetation.
Thus, as a result of human impacts, little of the Post Oak Savannah is as it was during
presettlement times.
VEGETATION OF THE POST OAK SAVANNAH
As mentioned above, while probably dominated originally to a significant extent by savannahs/open
woodlands/forests of post oak and blackjack oak with a tall grass understory, the
Post Oak Savannah was a complex mosaic of plant communities. The communities listed
below, modified in part from Wilson (1989), Bezanson (2000), and MacRoberts et al.
(2002b), represent the primary plant communities and give some indication of the complexity
of the vegetation of the Post Oak Savannah. It should be noted, however, that there were and
still are small areas of different, and in some cases, quite distinctive communities. An excellent
example of this can be seen at the Gus Engeling Wildlife Management Area in Anderson
Co., where Singhurst et al. (2003b) recently documented a number of interesting “vegetation
alliances,” some of which have similarities to communities of the Pineywoods. These include
the Sand Post Oak-Bluejack Oak Alliance (Quercus margaretta-Q. incana), the White Oak-
Southern Red Oak-Post Oak Alliance (Quercus alba-Q. falcata-Q. stellata), the Loblolly Pine-
Southern Red Oak Alliance (Pinus taeda-Quercus falcata), the Overcup Oak Seasonally
Flooded Forest Alliance (Q. lyrata), and the Planer Tree Seasonally Flooded Forest Alliance
(Planera aquatica).
POST OAK-BLACKJACK OAK UPLAND SAVANNAHS, WOODLANDS, AND FORESTS—The dominant natural
vegetation for much of the upland Post Oak Savannah was an open deciduous
savannah/woodland/forest composed of Quercus stellata (post oak), Q. marilandica (blackjack
oak), and other drought-tolerant species (e.g., Carya texana, black hickory) (Bezanson 2000)
and an understory of tall grasses such as Schizachyrium scoparium (little bluestem),