Abstract
Longleaf pine (Pinus palustris) savannas were once dominant across the southeastern U.S., including East Texas and parts of western and central Louisiana. The diverse understory associated with these historical savannas may occasionally be seen today, but not often in longleaf pine ecosystems. This project aimed to define east Texas site characteristics that are necessary to support these ecosystems with a dense and diverse herbaceous understory with little to no midstory cover. Fifty-nine plots across three study sites were established to evaluate the influence of overstory cover, basal area, aspect, elevation, and slope on the number of plant genera present. Forest structure and site characteristics had significant effects on the number of plant genera found. The number of genera increased with higher elevation and slope; as elevation increased, there was a decline in basal area and overstory cover, leading to a more diverse, understory layer. In order to re-establish and maintain a diverse, herbaceous understory in longleaf pine savannas, sites with more open canopies and on slopes with the most solar exposure should be given priority, particularly when planting desired understory species.
Highlights
The historical range of longleaf pine (Figure 1) extended from the Atlantic Coast to East Texas (Mohr & Roth, 1897) and contained over 37 million hectares of longleaf pine forest (Frost, 1993)
Locations were chosen “subjectively but without preconceived bias” (Mueller-Dombois & Ellenberg, 1974) by establishing plots in suitable understory chosen based on visual affirmation of a diverse herbaceous understory with few midstory trees or shrubs, but not all plots were located in areas with these conditions as some plots were located within longleaf pine ecosystems but with more midstory cover
Less tree cover led to more coverage of grasses, and an increase in elevation led to a decrease in basal area and overstory cover
Summary
The historical range of longleaf pine (Figure 1) extended from the Atlantic Coast to East Texas (Mohr & Roth, 1897) and contained over 37 million hectares of longleaf pine forest (Frost, 1993). Longleaf pine (Pinus palustris) was once dominant in East Texas and parts of western and central Louisiana as practically pure stands (Bray, 1904), with a dense herbaceous understory, relatively low midstory cover, and mature longleaf pine trees dominating the overstory. The understory in longleaf pine ecosystems was diverse herbaceous vegetation of grasses and forbs. Longleaf pine ecosystems require periodic prescribed fires, in the absence of wildfires, to sustain an understory that will not compete with the longleaf pine overstory, and to support the historic savanna ecotype. Longleaf pine forests historically occurred on different landforms ranging from well-drained, xeric sandhills and rocky mountainous regions to poorly-drained flatwoods (Boyer, 1990), each supporting unique understory communities
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