Forest Vegetation of the Big Thicket, Southeast Texas

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Abstract
Tree and shrub species composition and environmental characteristics were measured in 56 stands representing the range of natural vegetation types of the lower coastal plain of southeast Texas, and vegetation characteristics were related to the physical environment. Most of the stand—to—stand variation in species composition was expressed by the first axis of a reciprocal averaging ordination, and stand position along the first axis in turn was most highly correlated with percent sand in the surface soil (0—15 cm) (r = —.81, P <.05). The first ordination axis is interpreted as a soil moisture gradient. A more weakly expressed second axis of variation is interpreted as a soil aeration—parent material gradient (from high organic matter, low extractable Ca stands to low organic matter, high Ca stands). Overstory basal area, woody plant species richness of overstory and understory, and relative basal area of broad—leaved evergreens in both strata all varied in a regular way along the first ordination axis, having low values at the dry end, peaking in the wet—mesic range, and declining somewhat toward the wet end. Comparison of vegetation types in southeast Texas with those for the while of the southeastern. United States coastal plain showed widespread congruence of types. Major discrepancies were the lack of a pine flatwoods type in Texas and the presence in Texas of a flatland hardwood type and a pine—oak type more characteristic of the Piedmont further east. The question of fire, succession, and climax on the coastal plain is considered and it is suggested that the timing of different studies in the last 50 yr may have influenced results and interpretation.