ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...
ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...
ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...
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88 INTRODUCTION/PRESETTLEMENT VEGETATION TYPES <strong>OF</strong> PINEYWOODS<br />
longleaf pine-dominated woodlands by mixed forests of loblolly pine and broad-leaved<br />
deciduous hardwoods (Frost 1993). In addition, large areas have been cleared for ranching<br />
and agriculture, reservoirs have covered many acres of former river floodplains, and more<br />
and more areas are becoming urbanized.<br />
Despite the importance of understanding historic vegetation for both science and conservation,<br />
only a few published studies quantitatively estimating presettlement vegetation<br />
exist for the Pineywoods and adjacent areas (Evans 1997). Much of what is known has been<br />
either reconstructed from witness tree data (Delcourt 1976; Schafale & Harcombe 1983),<br />
derived from early published descriptions in combination with detailed knowledge of existing<br />
relationships between vegetation, soils, and physiography (Brown 1944; Marks & Harcombe<br />
1981; Harcombe et al. 1993; Van Kley & Hine 1998; Van Kley 1999a, 1999b), or reconstructed<br />
from early timber company surveys (Evans 1997). The following accounts are largely<br />
adapted from the description of Pineywoods and western Louisiana historical vegetation in<br />
the Ecological Classification System of Turner et al. (1999).<br />
LONGLEAF PINE COMMUNITIES—Texas longleaf pine woodlands represented the western edge of<br />
“an unbroken forest of the same general character” which extended eastward to Virginia (Bray<br />
1906; Frost 1993). Early data from uncut forests (Mohr 1897; Schwartz 1907; Chapman<br />
1909) reveal mostly uneven-aged stands with the oldest and largest trees 400 or more years<br />
old and up to about 98 cm (40 inches) (rarely to about 60 inches—Block 1995) in diameter<br />
at breast height (dbh). Bailey (1905) described Texas longleaf pine as “miles of dense forest of<br />
the cleanest, most uniform and symmetrical body of timber to be found on the continent.”<br />
Often occurring in pure stands, longleaf pine dominated most upland areas in the southern<br />
and eastern Pineywoods but diminished to the west and north. Wet longleaf pine savannahs<br />
with a ground layer of grasses, sedges, and specialized wetland plants occurred on the poorlydrained,<br />
nearly level topography along the southern (Big Thicket) edge of the region. Longleaf<br />
pine woodlands with a diverse ground layer of grasses, composites, and legumes (Bridges &<br />
Orzell 1989a) were prevalent to the north on drier, more topographically variable uplands<br />
where, as today, communities similar to wet pine savannahs (Herbaceous Seeps or “bogs”)<br />
occurred as isolated inclusions in areas of groundwater seepage. Low-intensity surface fires<br />
ignited by lightning strikes and, during the last 12,000 years, also set by Native Americans<br />
burned the grasses and fallen pine needles every 2 to 8 years and maintained a grassy, open<br />
woodland by destroying competing woody plants (Heyward 1939; Grelen & Duvall 1966;<br />
Komarek 1968; Christensen 1981). These fires were more common in the spring and summer<br />
when thunderstorms are more frequent (Christensen 1981) and, once ignited, could burn for<br />
days across large areas of uplands. Longleaf pine, which has adaptations enabling both adults<br />
and seedlings to survive fire (Platt et al. 1988), would then dominate on such sites. These were<br />
clearly pyrogenic (= resulting from fire; fire dependent) communities and the critical role of fire<br />
in their maintenance is now widely recognized (e.g., Christensen 1981). Following the logging<br />
era of 1880–1930 and the virtual elimination of fire during the twentieth century, mixed second<br />
growth stands of loblolly pine and deciduous hardwoods developed. Today, longleaf pine is<br />
dominant on only about 1.5% of its former range (Frost 1993; Outcalt 1997; Estill & Cruzan<br />
2001).<br />
SHORTLEAF PINE COMMUNITIES—Uplands in the northern and western Pineywoods were largely<br />
dominated by mixed stands of shortleaf pine and a variety of dry-site oaks and hickories.<br />
Mohr (1897) described how longleaf pine forests “toward their northern limit… gradually<br />
pass into a mixed growth of deciduous trees and shortleaf pine.” Gow (1905) referred to these<br />
shortleaf pine-oak-hickory forests as “high hammocks” and indicated that their “appearance<br />
differs totally from (longleaf) pine uplands,” being “characterized by dense thickets of shortleaf<br />
pine seedlings, often stunted by shade of hardwoods under which they grow.” The oldest<br />
and largest trees in these mixed-age stands were more than 200 years old and 86 cm (35<br />
inches) or more dbh, (Turner et al. 1999). Most virgin shortleaf pine in the region had been