Biological diversity, or biodiversity, is declining on a global scale at unprecedented rates. These declines are largely the result of human activities and resource use. Intensive forestry is often cited as a contributing factor in biodiversity declines. Because forestry practices are being placed under increased scrutiny with respect to biodiversity impacts, the objective of this project was to determine the effects of specific silvicultural practices on plant diversity in pine plantations on wet flats in Virginia. The study area consisted of three sites in the Coastal Plain. The sites were originally established in 1969 to study the effects of various treatments on loblolly pine growth. The three treatments applied were chop and burn, bedding, and ditching. Fertilization subplots of P, N and P, N, P, and lime, and a control were added to the treatment areas in 1978. This study was conducted in 1991 when stands were 23 years old, nearing rotation age. Bedding exerted the greatest effect on plant diversity. Diversity was lower on the bedded treatment, although total biomass was higher. Bedding appears to increase pine growth by providing seedlings with more available soil volume and by reducing the vegetative regeneration of hardwoods and shrubs, thereby decreasing site diversity. Ditching likewise increased pine growth by lowering water table levels, but ditching had little effect on plant diversity. Fertilization exhibited only minor effects on diversity, and those effects that were observed did not reveal any definitive trends. Of the treatments applied, liming appeared to increase pine growth most, possibly due to increased calcium availability. Water table level was highly correlated to mid story diversity, though it was less correlated to other canopy layers. In addition, correlation analyses indicated a significant degree of interaction between canopy layers. It appears that diversity, particularly in the lower canopy layers, is affected directly by treatments and indirectly by shifts in overstory characteristics. Intensive forest management involving hydrology-altering site preparation and fertilization impacted plant diversity within these wet flat plantations. Whether such changes affect wildlife habitat or ecosystem functioning requires further study. / Master of Science

Intercropping is defined as a management approach where two or more crops are planted on the same forested site simultaneously. The advantages of applying this concept on young pine plantations in the south can increase site utilization, reduce weed competition, provide annual or semi-annual revenues early in the timber rotation, ameliorate the soil, and diversify production. Research was initiated to determine the feasibility of using various plants as intercrops on pine plantations in Virginia and North Carolina. Regional crops were categorized into four groups based on management intensity, end use, and crop value. These crop groups included: 1. Field Crops: Corn, Sorghum, Cotton, Small Grains, 2. High Value Crops: Tobacco, Peanuts, Snap Beans, Tomatoes, Cucurbits, 3. Forage Crops: Grasses and Legumes, 4. Biomass Crops: sycamore, Sweet Gum, European Black Alder, Cottonwood. The ecological and management characteristics of these crops were examined to determine their compatibility with pine plantation management. In every case, three significant constraints were noted; intercropping on plantations reduced the number of trees carried to maturity by 50 to 60 percent; intercrop production was highly sensitive to row spacings and required seedling row widths of 4 to 8 m; and great emphasis was placed on site preparation, with per hectare costs increasing by approximately 250 percent. Investment analysis of several hypothetical intercrop scenarios suggested that forest intercropping can be financially rewarding under a variety of crop combinations. Intensively managed intercrops provided substantially greater returns than a conventional plantation investment. A field crop-pine combination was the most attractive intercrop scenario for large scale plantation intercropping, due to consistently high profit margins, low total investment costs, and fewer marketing constraints. Vegetable-pine combinations were typically high cost alternatives which generated equally attractive net revenues. However, the high costs and intensive management requirements restricted the introduction of vegetable crops to small plantation acreages where adequate attention would be available. Forage and biomass intercrops were relatively inferior investments relative to the more intensive vegetable and field crop combinations. Wide intercrop spacings dramatically increased average DBH of simulated pine stands configured for intercrop management, resulting in greater sawlog and veneer size log production and lower yields of pulpwood sized timber. Although the difference in net revenue from the pine component marginally favored the intercropped plantation, the difference in product mix suggests that companies or individuals interested in diverse timber products may wish to consider plantation intercropping as one means of diversifying plantation timber yields. Further study is suggested to quantify the biological effects of forest intercropping on component crops, with emphasis on intensively managed crops. Practical application is restricted to fertile, highly productive plantation sites capable of supporting both agricultural and forest crops. / Ph. D.