Appendices & Glossary - Botanical Research Institute of Texas

1336 APPENDIX TWENTY-ONE/COMMERCIALLY IMPORTANT TIMBER TREES OF EAST TEXAS
QUERCUS STELLATA Wangenh. POST OAK
(FAGACEAE, BEECH OR OAK FAMILY)
Other Common Names: IRON OAK, CROSS OAK
Form and Size: shrubby to small or medium-size tree to 20(–30) m; trunk straight to crooked, 0.3–1 m in diameter, often
stunted in dryer western parts of East Texas and the adjacent Cross Timbers; crown broad and rounded.
Leaves: deciduous, simple, alternate, the blades 4–15(–20) cm long, 2–10(–12) cm wide, rather stiff in texture, dark green
and shiny above, lower surface lighter and covered with minute, stellate (= star-shaped) hairs visible with moderate
magnification, turning brownish or sometimes yellowish brown in autumn, basally rounded-attenuate to cordate,
sometimes cuneate, marginally shallowly to usually deeply lobed, the typically 2–3 lobes on each side rounded to
spatulate or with irregular shallow lobes, entire, usually the main lobe on each side rather large and perpendicular to
midvein, giving the leaf a roughly cross-like appearance, without bristle tips; petiole 3–7(–30) mm long, with stellate
hairs.
Buds: to ca. 4 mm long (terminal), reddish brown, ovoid, apically obtuse or acute, sparsely hairy.
Flowers: unisexual, male and female flowers occurring separately (plants monoecious), individually tiny and inconspicuous;
male flowers numerous in slender, dangling catkins 5–10 cm long; female flowers stalkless, in 1–4-flowered clusters
in the leaf axils
Fruits: acorns, often 1–3 clustered, maturing in 1 season; cup enclosing 1/4–2/3 nut; nut ovoid or globose, 10–20 mm long,
8–12(–20) mm wide.
Bark: light to dark gray, sometimes somewhat reddish brown, thin and scaly at first, developing deep lengthwise furrows
separating the rounded, sometimes broad, scaly ridges.
Wood: sapwood whitish to light brown, thin or thick; heartwood rich light brown to dark brown; wood hard, heavy, durable,
usually straight-grained; growth rings distinct except in slow-grown stock, nearly indistinguishable from other white
oaks.
Habitat: Usually on dry sites, including dry sandy and gravely-silty uplands and ridges, often in association with BLACK-
JACK OAK. While POST OAKS are remarkably tough in natural situations (e.g., withstanding dry conditions and repeated
droughts), they are extremely sensitive to disturbance of their roots and die quickly (e.g., in yard settings) when their
root zone has been compromised (e.g., by compaction).
Range: occurring in all areas of Texas except the High Plains and Trans-Pecos and dominant in the Cross Timbers and
Post Oak Savannah; widespread in the southeastern U.S. and adjacent areas west to KS, OK, and TX.
Principal Uses: limited use (commercially sold as WHITE OAK) in furniture, also flooring (widely used because of hardness,
resistance to abrasion, and ability to finish smoothly), railroad ties, siding, planks, construction and mine timbers, trim
molding, stairs, fence posts, pulp, veneer, particle boards, and fuel. The bark is a source of tannin.
Historical Uses: fence posts (since durable in contact with soil; hence the common name), railroad ties, flooring, lumber,
fuel. The acorns of post oak, like those of other white oaks, are rich in fat, protein, and starch as well as being relatively
low in tannins (compared to red oaks). Consequently, these acorns were used by Native Americans as food (when
ground into meal) and by early settlers as forage for pigs.
Other Significant Information: POST OAK is the widest-ranging oak in Texas and the dominant tree in the sandy-soil areas
of North Central and East Texas, where it dominates (sometimes in nearly pure stands) the Post Oak Savannah and
Cross Timbers in the forest-prairie transition area. This is a slow growing, long-lived species. Tree-ring chronologies
extending from about 200 to more than 300 years have been obtained from East Texas POST OAKS, with the oldest individual
trees dating back to 1658 (D. Stahle, pers. comm.). In some areas, particularly the Cross Timbers, the stunted size
and the poor quality of the wood obtainable from these ancient, often hollow and damaged trees have made them not
worth cutting from the commercial standpoint. As a result, a number of old-growth areas of “Ancient Cross Timbers”
still survive. Conservation efforts are underway to preserve these forests, which date back to presettlement times (see
page 125 of the introduction to this volume). Though sensitive to disturbance of its roots (and very difficult to transplant),
this species is sometimes used as a shade tree. It is also planted to stabilize dry rocky slopes where few other trees can
grow. Like many oaks, POST OAK is a mast-fruiting species—in other words, it produces a heavy crop of fruits only at
irregular intervals—this type of cyclical fruiting, with years of heavy fruit production occurring irregularly, is possibly
an adaptation to reduce seed predation by making the seeds an unpredictable resource. Toxicity of oaks to cattle due to
the presence of tannins can cause significant loss in some areas, particularly during drought years; mostly new foliage
is involved, but mature leaves and acorns can also cause poisoning if eaten in large quantities; the compounds actually
causing the toxic effects are apparently low molecular weight phenolic compounds produced as the result of biodegradation
of more molecularly complex tannins. POST OAK is sometimes confusing to identify, due to its variable leaf shape
and many different growth forms.
Recognition in the Field: leaves usually cross-shaped and lacking bristle tips; twigs and the lower surface of leaves with
dense stellate (star-like) hairs; fruit an acorn with cup enclosing 1/4–2/3 of nut.