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

100 INTRODUCTION/CURRENT VEGETATION OF PINEYWOODS
to streams historically protected these sites from fires, most of which would have had to
burn downhill to reach them. Moreover, lower hydrologic position on the landscape results
in more available soil moisture and nutrients than for uplands. In presettlement times, firesensitive
species including loblolly pine were probably more restricted to these sites than
they are today.
Of all Pineywoods forest types, Mesic Lower Slopes and Terraces have the closest affinity
with the Eastern Deciduous Forests of the Appalachians, the Midwest, and the northeastern
U.S. (Braun 1950; Blackwelder 2000). Natural stands develop a diverse mixture of
Pinus taeda (loblolly pine) and various deciduous hardwoods, including Quercus falcata
(southern red oak), Q. alba (white oak), Q. nigra (water oak), Nyssa sylvatica (black-gum),
and Liquidambar styraciflua (sweetgum). Fagus grandifolia (American beech) and Magnolia
grandiflora (southern magnolia) often grow on undisturbed sites. Ilex opaca (American
holly), Ulmus alata (winged elm), Acer barbatum (Florida maple), Cornus florida (flowering
dogwood), Ostrya virginiana (eastern hop hornbeam), Callicarpa americana (American
beauty-berry), and Viburnum acerifolium (maple-leaf viburnum) are important in the
understory. Chasmanthium sessiliflorum (narrow-leaf wood-oats), Parthenocissus quinquefolia
(Virginia creeper), Mitchella repens (partridge berry), Smilax pumila (sarsaparilla-vine), and
Sanicula canadensis (black snakeroot) are common ground layer species. Vines such as Vitis
rotundifolia (muscadine grape) commonly festoon the trees. Less frequent are “vernal herbs”
more typical of the deciduous forests of the Appalachians or the Midwestern U.S:
Podophyllum peltatum (mayapple), Erythronium albidum (white trout lily), Arisaema triphyllum
(jack-in-the-pulpit), A. dracontium (green-dragon), and Sanguinaria canadensis (bloodroot).
Such spring ephemerals typically flower in early spring as soon as suitable temperatures
permit and before the canopy closes and available light is thus greatly reduced (Schemske
et al. 1978).
Preliminary observations suggest the existence of both a “sandy soil” variant more likely
to support high populations of Mitchella repens, Smilax pumila, Fagus grandifolia, Magnolia
grandiflora, and others and a “rich-mesic” variant on nutrient-rich clayey-loamy soils where
“vernal herbs” such as Podophyllum peltatum, Arisaema dracontium, Erythronium spp., and
Polygonatum biflorum (great Solomon’s seal), along with Tilia americana (American basswood),
are more likely to occur. However, we have not yet documented these differences
with quantitative data.
MESIC STREAM BOTTOMS—On the narrow floodplains of small tributary streams, a mixed
loblolly pine-broad-leaved deciduous forest very similar to that of adjacent Mesic Lower
Slopes develops (Fig. 58). It is also known as “mesic creek bottom” (Nixon 2000), and “floodplain
hardwood-pine forest” (Marks & Harcombe 1981). The small streams usually have a
deep, well-developed stream channel and a narrow floodplain and drain only a small portion
of the watershed. As a result, flooding is brief and infrequent. Occasionally, species characteristic
of wetter sites, including Quercus laurifolia (laurel oak), Boehmeria cylindrica (false nettle),
and especially Carpinus caroliniana (American hornbeam), may also be found, especially in
low areas or adjacent to the stream channel.
WET-MESIC STREAM BOTTOMS—Downstream from Mesic Stream Bottoms, streams become
larger, floodplains wider, floods more frequent, and flood duration longer. Often associated
with third-order perennial streams, Wet-Mesic Stream Bottoms are transitional between Mesic
Stream Bottoms and downstream Seasonally Flooded River Floodplains. The hydrologic
regime corresponds to that of Zone V of Clark and Benforndo (1981), which is described as
“irregularly inundated” in the Wetlands Delineation Manual (U.S. Army Corps of Engineers
1987). Flooding is not severe enough to eliminate many mesic species, but flood-tolerant
species such as Q. laurifolia (laurel oak), Q. phellos (willow oak), Betula nigra (river birch), and
Boehmeria cylindrica (false nettle) occur—especially in depressions and old stream channels.