Academic journal article The American Midland Naturalist

Historical Change in Vegetation and Disturbance on the Georgia Piedmont

Academic journal article The American Midland Naturalist

Historical Change in Vegetation and Disturbance on the Georgia Piedmont

Article excerpt

ABSTRACT.-Due to the extensive removal of the forest cover of the southeastern piedmont during the 19th century and to the lack of systematic presettlement records for most of this region, there has been little basis for relating the piedmont's maturing postsettlement secondary forest to its pre-European condition. This study compares species composition patterns between pre-European and present periods for a portion of the Georgia piedmont that had a systematic presettlement land survey. Detrended correspondence analysis of presettlement, immature postsettlement, and mature postsettlement forests identifies a primary gradient that distinguishes between the vegetation of these periods on the basis of habitat moisture preferences and fire tolerance of species. A secondary gradient emphasizes life history characteristics of species that typically differentiate immature and mature postsettlement forests; presettlement forests were not dominated by the late successional species typical of mature postsettlement forests, but had abundant disturbance-favored taxa. Changes in the abundance of individual species from presettlement to mature postsettlement forests occurred across all habitat types. The xerophytic, fire-tolerant taxa that dominated presettlement forests (e.g., Pinus species, Quercus stellato, Q. velutina) are less important in mature postsettlement forests. Dominants of mature postsettlement forests (e.g., Q. alba, Liriodendron tulipifera, Carya species) are primarily mesophytic, fire-intolerant species that were far less prominent in presettlement forests. Marked contrasts in composition between presettlement and mature postsettlement forests of the piedmont have been produced by changes in the prevalent disturbance regime from fire-dominated dynamics to gap-phase processes.

INTRODUCTION

The nature of secondary succession is fundamental to interpreting the character of eastern North American forests, since most have regrown following widespread clearing during the eighteenth and nineteenth centuries. The traditional ecological presumption that forest stands would ultimately revert to their original, presettlement character is challenged by recent attention to the consequences of altered disturbance regimes, particularly fire suppression. Studies show these influences produce communities markedly different from their presettlement predecessors in many areas of the Northeast (Whitney, 1990; Foster et aL, 1992; Motzkin et aL, 1993; Abrams et al., 1995; Abrams and McCay, 1996) and Midwest (McCune and Cottam, 1985; Whitney, 1987; Clark, 1990; Fralish et al., 1991; Palik and Pregitzer, 1992; White and Mladenoff, 1994; Frelich and Reich, 1995). Although the southeastern piedmont is among the best studied examples of forest development following clearing (Oosting, 1942; Christensen, 1977; Peet and Christensen, 1980; Christensen and Peet, 1984), relatively little is known about the relationship of today's maturing secondary stands to the presettlement forests of this region.

Interpretations of the piedmont successional process have often equated pre-European forest, uncut forest remnants and climax vegetation. Oosting (1942) wrote "when occasional hardwood stands are found which include trees 200-300 years of age and which show little evidence of recent disturbance, they must be accepted as samples of the extensive hardwood forests which preceded the white man" (p. 89). Skeen et aL (1993) inferred that while disturbance occasionally occurred, native forest stands were predominantly stable. These variants of the traditional model of succession (see Christensen, 1993) emphasize development in the absence of disturbance.

This paper emphasizes the role of disturbance regimes in both presettlement and postsettlement piedmont forests, exploring the hypothesis that maturing secondary stands do not reproduce precolonial forest, but rather are developing toward a new state dependent on modifications to the prevailing disturbance regime. …

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