Browsing by Author "Schiffman, Paula M."
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- Carbon storage during the regrowth and conversion of Virginia Piedmont forestsSchiffman, Paula M. (Virginia Tech, 1985-06-05)Recent increases in atmospheric carbon dioxide caused by the combustion of fossil fuels and tropical deforestation may result in global warming. Carbon accumulation by regrowing temperate forests, in regions such as the southeastern United States, may have been extensive enough to counterbalance releases of carbon from the tropics. In the Virginia Piedmont, large amounts of carbon have accumulated in phytomass and detritus of loblolly pine (Pinus taeda) plantations and natural forests regrowing on post-agricultural fields. After 50 years, carbon in phytomass of old field plantations was 200,000 kg/ha, twice the amount accumulated by natural forests. Detrital carbon accumulations totaled over 100,000 kg/ha, but were dependent upon amounts of erosional loss prior to reforestation. The forested land area in the southeastern United States has stabilized, and forest conversion is now the primary form of reforestation. Therefore, the region's ability to continue to store carbon has been questioned. Still, the phytomass of late-rotation converted plantations stored 200,000 kg carbon/ha, twice the amount of the natural forests they replaced. In addition, while the harvest of natural forests resulted in small reductions in detrital carbon, it was rapidly restored to over 100,000 kg/ha within 30 years. Houghton et al. (1983) developed a series of models describing carbon dynamics during reforestation. My data show that patterns of carbon accumulation exhibited by regrowing loblolly pine plantations are different from their models. Therefore, modifications of the models are suggested to improve estimates of carbon storage in temperate forests.
- Environmental determinism and forest structure and composition: a naturally replicated experimentSchiffman, Paula M. (Virginia Tech, 1990)Ecological theory states that forest succession is largely environmentally determined. Many investigators have suggested, however, that stochastic processes can frequently alter successional pathways. In particular, the colonization phase is thought to be very stochastic. This study utilizes a unique series of 6 naturally replicated sites on Brush Mountain (Montgomery Co., VA) to determine whether forest structure and species composition is primarily deterministic or stochastic in nature. Although the canopy stratum of the mature forest at these environmentally similar sites was very Similar in structure and species composition (p>0.05), the composition of the subcanopy strata vegetation differed Significantly among sites (p<0.05). This indicated that stochastic events (e.g. low intensity ground fires, deer browsing, cattle grazing) were were important factors during the development of understory and ground layer vegetation. Site-to-site differences in subcanopy species composition remained apparent during the first 2 years following disturbance (removal of canopy cover) of 4 sites. Brush Mountain lacked a significant seed bank (< 1 seed/m²), and the dominant sub canopy species reproduced largely by vegetative sprouting. Post-disturbance colonization of the sites was very stochastic, but had relatively little immediate effect on vegetation structure and composition. In the future, however, as colonist species reproduce and increase in density, stochastic colonization events may become an important aspect of forest development at some of the sites.