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We quantified the effects of three wildfire hazard reduction treatments (prescribed fire, thinning from below, and the combination of fire and thinning), and passive management (control) on mineral soil organic C, and enzyme activity in loblolly pine (Pinus taeda L.) forests on the Piedmont of South Carolina. Soil organic C was reduced by thinning, either alone or with prescribed fire, and this effect persisted through the fourth post-treatment year. Fire also resulted in reduced soil organic C, but not until several years after treatment. Soil C/N ratio initially increased after fire, either alone or with thinning, but this difference did not persist. The activities of three soil enzymes (acid phosphatase, chitinase, and phenol oxidase) in the upper mineral soil were quantified as measures of microbial activity. During the fourth post-treatment year we observed significant stimulation of all three enzyme systems as a result of thinning or thinning and burning. Although the patterns of variation in acid phosphatase and chitinase activity among treatments were similar during the first and fourth post-treatment years, the first-year treatment effects were not statistically significant. Given the management objective of utilizing these stands for timber production, the increased potential for rapid nutrient turnover offered by thinning gives this approach advantages over prescribed fire; however, management for maximum long-term storage of soil C may be better facilitated by prescribed fire.

Four genotypes of shortleaf pine (Pinusechinata Mill.) were grown in open-top chambers in the Piedmont Region of South Carolina. The seedlings were exposed to several combinations of ozone (near zero, ambient, 1.7 × ambient, or 2.5 × ambient) and acid rain (pH 3.3, 4.3, or 5.3). Glucose, sucrose, total reducing sugars, and starch contents of the pine needles were determined initially and at 5- to 12-week intervals during the following 38 weeks of exposure. Needles exposed to acid rain and ozone treatments followed the seasonal trends normally encountered in carbohydrate content, but there were some statistically significant differences in the quantities of individual carbohydrate components after prolonged exposure. In general, those needles exposed to higher levels of ozone (1.7 or 2.5 × ambient) had lower levels of starch and sucrose, with higher levels of both glucose and total reducing sugars. The starch levels in needles exposed to elevated ozone showed decreased values throughout the dormant period at all pH levels. Similarly, the sucrose levels were significantly lower in the high ozone and high acid rain treatment after 38 weeks of exposure. These results indicate that air pollutants may be affecting the carbon allocation balance within the needles.

Ecosystem classification identifies interrelationships within and among the geomorphology, soils, and vegetation that converge to form ecosystems across forest landscapes. We developed a multifactor ecosystem classification system for a 13 000 ha southern Appalachian landscape acquired in 1998 by the South Carolina Department of Natural Resources. Using a combination of multivariate analyses, we distinguished five ecosystem types ranging from xeric oak (Quercus spp.) to mesic eastern hemlock (Tsuga canadensis (L.) Carrière) ecosystems. Ecosystems segregated along geomorphic gradients influencing potential moisture availability, with soil properties such as solum thickness distinguishing among ecosystems occupying similar topographic positions. Our results suggest that different combinations of geomorphic and soil factors interact to form similar ecosystems across the landscape, and a given environmental factor can impact ecosystem development at some constituent sites of an ecosystem type but not at other sites. A regional comparison of ecosystem classifications indicates that environmental variables important for distinguishing ecosystems in the southern Appalachians vary, with Jocassee Gorges characterized by unique suites of environmental complexes. Our study supports the contention that the strengths of ecosystem classification are providing (i) comprehensive information on the interrelationships among ecosystem components, (ii) a foundation from which to develop ecologically based forest management plans, and (iii) an ecological framework in which to conduct future research on specific ecosystem components or processes.

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