Piedmont Of Virginia Research Articles

Post-middle Miocene origin of modern landforms in the eastern Piedmont of Virginia

Diverse late middle Miocene dinoflagellate floras, obtained from two sites along the western edge of the Atlantic Coastal Plain in central Virginia, indicate that the eastern Virginia Piedmont was covered by marine waters about 12-13 Ma. This transgression extended farther westward across the Virginia Piedmont than any other transgression that has been documented. Extensive fluvial deposits that may be associated with this transgression covered earlier stream patterns in the eastern Piedmont and buried them beneath a thin (probably less than 100 foot-thick) veneer of sand and gravel. During the subsequent regression, a linear down-slope stream-drainage pattern developed. Although it has been somewhat modified by later stream captures, it still is easily recognizable. This interval ofmarine inundation and deposition explains why modern stream patterns in the eastern Piedmont of Virginia strongly resemble the stream patterns in the Coastal Plain and differ from the structurally adjusted trellis stream patterns typical of thewestern Piedmont, Blue Ridge, and Valley and Ridge regions. Uplift of the modern Southern Appalachian Mountains began at the time of this transgression and was largely completed by the late Pliocene.

The effect of weed control and fertilization on survival and growth of four pine species in the Virginia Piedmont

The growth response of loblolly pine ( Pinus taeda L.), shortleaf pine ( Pinus echinata Mill.), Virginia pine ( Pinus virginiana Mill.), and white pine ( Pinus strobus L.) to weed control and fertilization in the Piedmont of Virginia was assessed. Four different silvicultural treatments were evaluated: (1) check (no treatment); (2) weed control; (3) fertilization; (4) weed control plus fertilization. The weed control treatment included a series of herbicide and mechanical treatments to eliminate competing hardwoods. The fertilizer treatments added N, P, K, and S. Survival and growth was measured annually through age 5. There were significant differences in survival and growth among species. Survival was greatest for loblolly pine, lower in shortleaf and Virginia pine, and lowest in white pine. Fertilization without controlling the competing hardwoods decreased survival in all planted pines due to the increased hardwood competition. Loblolly pine was tallest through the 5-year period, shortleaf and Virginia pine were shorter and white pine was shortest. Silvicultural treatments had no impact on tree height but significantly affected DBH. Weed control increased DBH while fertilization did not. When applied in combination with weed control, there was no additional increase in growth of the pines due to fertilization beyond that from weed control only. Fertilization stimulated the growth of the competing hardwoods which were significantly taller in the fertilized plots.

Evaluation of repeated measurements of radon-222 concentrations in well water sampled from bedrock aquifers of the Piedmont near Richmond, Virginia, USA: Effects of lithology and well characteristics

Radon ( 222Rn) concentrations in 26 ground water wells of two distinct lithologies in the Piedmont of Virginia were measured to assess variation in ground water radon concentrations (GWRC), to evaluate differences in concentrations related to well characteristics, lithology, and spatial distributions, and to assess the feasibility of predicting GWRC. Wells were sampled in accordance with American Public Health Association Method 7500 Rn-B, with modifications to include a well shaft profile analysis that determined the minimum purge time sufficient to remove the equivalent of one column of water from each well. Statistically significant differences in GWRC were found in the Trssu (1482±1711 pCi/L) and Mpg (7750±5188 pCi/L) lithologies, however, no significant differences were found among GWRC at each well over time. Using multiple regression, 86% of the variability ( R 2) in the GWRC was explained by the lithology, latitudinal class, and water table elevation of the wells. The GWRC in a majority of the wells studied exceed US Environmental Protection Agency designated maximum contaminant level and AMCL. Results support modifications to sampling procedures and indicate that, in previous studies, variations in GWRC concentrations over time may have been due in part to differences in sampling procedures and not in source water.

Spatial pattern and process in forest stands within the Virginia piedmont

Abstract. Question: Underlying ecological processes have often been inferred from the analysis of spatial patterns in ecosystems. Using an individual‐based model, we evaluate whether basic assumptions of species’life‐history, drought‐susceptibility, and shade tolerance generate dynamics that replicate patterns between and within forest stands.Location: Virginia piedmont, USA.Method: Model verification examines the transition in forest composition and stand structure between mesic, intermediate and xeric sites. At each site, tree location, diameter, and status were recorded in square plots ranging from 0.25 to 1.0 ha. Model validation examines the simulated spatial pattern of individual trees at scales of 1–25 m within each forest site using a univariate Ripley's K function.Results: 7512 live and dead trees were surveyed across all sites. All sites exhibit a consistent, significant shift in pattern for live trees by size, progressing from a clumped understorey (trees ± 0.1 m in diameter) to a uniform overstorey (trees > 0.25 m). Simulation results reflect not only the general shift in pattern of trees at appropriate scales within sites, but also the general transition in species composition and stand structure between sites.Conclusions: This shift has been observed in other forest ecosystems and interpreted as a result of competition; however, this hypothesis has seldom been evaluated using simulation models. These results support the hypothesis that forest pattern in the Virginia piedmont results from competition involving species’life‐history attributes driven by soil moisture availability between sites and light availability within sites.

Spatial pattern and process in forest stands within the Virginia piedmont

Abstract. Question: Underlying ecological processes have often been inferred from the analysis of spatial patterns in ecosystems. Using an individual-based model, we evaluate whether basic assumptions of species’life-history, drought-susceptibility, and shade tolerance generate dynamics that replicate patterns between and within forest stands. Location: Virginia piedmont, USA. Method: Model verification examines the transition in forest composition and stand structure between mesic, intermediate and xeric sites. At each site, tree location, diameter, and status were recorded in square plots ranging from 0.25 to 1.0 ha. Model validation examines the simulated spatial pattern of individual trees at scales of 1–25 m within each forest site using a univariate Ripley's K function. Results: 7512 live and dead trees were surveyed across all sites. All sites exhibit a consistent, significant shift in pattern for live trees by size, progressing from a clumped understorey (trees ± 0.1 m in diameter) to a uniform overstorey (trees > 0.25 m). Simulation results reflect not only the general shift in pattern of trees at appropriate scales within sites, but also the general transition in species composition and stand structure between sites. Conclusions: This shift has been observed in other forest ecosystems and interpreted as a result of competition; however, this hypothesis has seldom been evaluated using simulation models. These results support the hypothesis that forest pattern in the Virginia piedmont results from competition involving species’life-history attributes driven by soil moisture availability between sites and light availability within sites.

Phycomicrobial Ecology of Acid Mine Drainage in the Piedmont of Virginia

Acid mine drainage encompasses 18 km{sup 2} of Louisa County, Virginia. Heavy metal laden acidic leachate flows from abandoned mines along the Piedmont`s Gold-Pyrite Belt. The oxidation of pyrite, sphalerite, chalcopyrite and other sulfide minerals that are disseminated throughout the mine tailings release H{sub 2}SO{sub 4}, Fe, Cu, Zn, Ni, Cd, As, Pb and other heavy metals into the Contrary Creek watershed and beyond, into Lake Anna. Downstream of these abandoned pyrite mines, high levels of acidity and heavy metals have made this a severely stressed environment incapable of supporting a healthy creek ecosystem. In an effort to assess in-situ, bioaccumulatory remediation of acid mine drainage by phycomicrobial mats, surveys have been conducted for 11 months in Contrary Creek; several extremophiles that are tolerant of acid mine systems have been found. Twelve to thirteen genera of algae and a few cocci and bacilli have been identified in surface waters. Predominant genera include Ulothrix, Pinnularia and Oscillatoria. Preliminary results demonstrate that the phycomicrobial communities found in this acid mine system maintain density and species diversity independent of pH and heavy metal fluctuations. These extremophiles also demonstrate high potential for heavy metal sorption. Phycomicrobial mats bioaccumulate 60--70% more heavy metals than concentrationsmore » found in surface waters and the creek. To date, remediatory attempts to restore Contrary Creek have not been successful. Results suggest that the extremophile ecology found in this system will facilitate the remediation process of other, similar acid mine affected ecosystems.« less

A linear programming approach for designing a herbaceous biomass delivery system

There are a number of systems-related issues associated with the harvest, storage, and transport of herbaceous biomass from on-farm storage locations to a centrally located plant. This modeling effort is directed toward the design of a biomass delivery system that considers storage, scheduling, and transportation issues. A statement of the problem, along with its salient characteristics, is presented, and a linear programming model is constructed. Uncertainty in production levels due to weather is addressed by reformulating the linear program as a two-stage problem with recourse. A specific case-study of a plant located in a country in the Piedmont of Virginia is described. The data for this study includes 20 producers having four to seven storage locations each. The model was solved using this data set and appropriate sensitivity analyses were conducted to illustrate the range of decision-making options that are available. The model minimized delivered cost by scheduling shipments from the various on-farm storage locations to meet a 5600 dry Mg monthly demand. The total cost (ownership+operating+labor) was $500/day/truck, and the resultant average cost of transportation ranged from $8 to $10/dry Mg. The average travel distance (farm+secondary+primary roads) was found to be 22 km for delivering the 67 200 dry Mg required for a year-round operation.

Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia

Research Article| November 01, 1996 Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia John N. Aleinikoff; John N. Aleinikoff 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar J. Wright Horton, Jr.; J. Wright Horton, Jr. 2U.S. Geological Survey, 926 National Center, Reston, Virginia 20192 Search for other works by this author on: GSW Google Scholar Marianne Walter Marianne Walter 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information John N. Aleinikoff 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 J. Wright Horton, Jr. 2U.S. Geological Survey, 926 National Center, Reston, Virginia 20192 Marianne Walter 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1996) 108 (11): 1481–1491. https://doi.org/10.1130/0016-7606(1996)108<1481:MPAFTM>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John N. Aleinikoff, J. Wright Horton, Marianne Walter; Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia. GSA Bulletin 1996;; 108 (11): 1481–1491. doi: https://doi.org/10.1130/0016-7606(1996)108<1481:MPAFTM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Uranium-lead dating of zircons from the Montpelier Anorthosite confirms previous interpretations, based on equivocal evidence, that the Goochland terrane in the eastern Piedmont of Virginia contains Grenvillian basement rocks of Middle Proterozoic age. A very few prismatic, elongate, euhedral zircons, which contain 12–29 ppm uranium, are interpreted to be igneous in origin. The vast majority of zircons are more equant, subangular to anhedral, contain 38–52 ppm uranium, and are interpreted to be metamorphic in origin. One fraction of elongate zircon, and four fragments of a very large zircon (occurring in a nelsonite segregation) yield an upper intercept age of 1045 ± 10 Ma, interpreted as the time of anorthosite crystallization. Irregularly shaped metamorphic zircons are dated at 1011 ± 2 Ma (weighted average of the 207Pb/206Pb ages). The U-Pb isotopic systematics of metamorphic titanite were reset during the Alleghanian orogeny at 297 ± 5 Ma. These data provide a minimum age for gneisses of the Goochland terrane that are intruded by the anorthosite. Middle Proterozoic basement rocks of the Goochland terrane may be correlative with those in the Shenandoah massif of the Blue Ridge tectonic province, as suggested by similarities between the Montpelier Anorthosite and the Roseland anorthosite. Although the areal extent of Middle Proterozoic basement and basement-cover relations in the eastern Piedmont remain unresolved, results of this investigation indicate that the Goochland terrane is an internal massif of Laurentian crust rather than an exotic accreted terrane. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Edaphic Factors and Forest Vegetation in the Piedmont of Virginia

FARRELL, J. D. AND S. WARE (Department of Biology, College of William and Mary, Williamsburg, VA 23185). Edaphic factors and forest vegetation in the Piedmont of Virginia. Bull. Torrey Bot. Club 118: 161-169. 1991.-To determine tree species distribution and abundance and possible edaphic factors correlated with these in Piedmont forests, we examined 51 upland hardwood stands in the northern, central, and southern Piedmont of Virginia. Soil Ca, Mg, and pH (but not soil texture) were positively correlated with the first axis of a detrended correspondence analysis (DECORANA) ordination, and % clay, Ca, and Mg were positively correlated with the second axis. Quercus alba was the most abundant species, important in stands all across the ordination and providing the background against which the abundance of other species varied. Quercus prinus, Q. coccinea, Nyssa sylvatica, Liriodendron tulipifera, Q. velutina, Q. rubra, Carya spp., and Fraxinus americana/Ulmus rubra were sequentially arranged along the first axis. Acer rubrum and the much less abundant species Q. falcata and Q. stellata were important at the high percent clay end of the second axis, while Q. coccinea was most important at the low percent clay portion of that axis. In an ordination of the understory layer of the 25 northern Piedmont stands, Liriodendron tulipifera, Acer rubrum, and Nyssa sylvatica were abundant only on the low Ca, low Mg, low pH end of the first axis, and Ulmus rubra, Fraxinus americana, and Cercis canadensis were found at the opposite end of the first axis. Cornusflorida and Carya spp. were spread broadly across the understory ordination, but were most important in its center, with Carya spp. most abundant on Triassic sites. None of the Quercus spp. which were dominant in the overstory were well represented in the understory. In both overstory and understory ordinations the stands at the high Ca, high Mg, high pH end of the first axis were northern Piedmont stands on Triassic formations, a geological substrate uncommon in most of the rest of the Virginia Piedmont. Since the forests of the non-Triassic portions of the Virginia Piedmont have traditionally been classified as oak-(pine)-hickory forests, the high importance of Carya spp. on the more restricted, Ca- and Mg-rich less acid Triassic substrates and their low importance in the areally extensive non-Triassic formations were unexpected.

Use of terrestrial arthropod prey by a stream-dwelling cyprinid fish

The spatio-temporal availability to, and use of terrestrial (allochthonous) prey by, a subset of the fish assemblage of a Virginia piedmont stream were investigated during spring and summer. Terrestrial invertebrates were most abundant in drift nets, but least common in fish stomachs, during April. In contrast, during August, terrestrial prey dominated the diet of the major cyprinid fish,Notropis ardens, even though terrestrial prey availability in the stream declined by an order of magnitude. Several other co-occurring fishes only rarely consumed prey of terrestrial origin. Drifting terrestrial invertebrates, were concentrated at the surface near the thalweg, compared to stream margin or substrate locations. This study suggests that morphologial and behavioral constraints of individual fish taxa, including predator avoidance responses, regulate the use of terrestrial prey within a given fish assemblage.

Variability of the Cecil Map Unit in Appomattox County, Virginia

AbstractA study was initiated in Appomattox County in the southern Piedmont of Virginia to assess composition and variability of a Typic Kanhapludult map unit. Five delineations of the Cecil (clayey, kaolinitic, thermic Typic Kanhapludults) map unit, three to eight sites within each delineation, and three profiles within each site were randomly located in a two‐level nested sampling scheme. Soil physical, chemical, and morphological data were collected from the Ap, Bt, and BC horizons of each profile. Fifty‐eight percent of the 81 profiles met the criteria for the Cecil soil series. Seventy‐one percent of the profiles were taxonomically similar to Cecil. The remaining 29% were taxonomically dissimilar inclusions. Thus, the map unit name would be Cecil and the map unit description would include dissimilar soils. Taxonomic variability was reflected in variability of taxonomically important soil properties. Percent base saturation decreased with depth in the profile. Maximum clay distribution occurred in the Bt horizon and ranged from 25 to 75%. The solum exhibited large variation in thickness. Subsoil properties important to mapping (percent base saturation in the chemical control section, clay percentage in the particle‐size control section, and solum thickness) exhibited considerable variation within delineations but the variability was consistent from delineation to delineation. Intrusions of mafic material into the felsic crystalline system, from which Cecil and similar soils form, accounted for most of the variability in the soil properties.

Post-Acadian metamorphism in the Appalachians

Summary Well-documented post-Acadian metamorphism occurs at three locales along the eastern flank of the Appalachians, where it has affected Avalonian basement and/or Carboniferous cover. Carboniferous rocks of coastal New Brunswick display a greenschist-facies metamorphism of Pennsylvanian to Permian age which largely post-dates associated Alleghanian ductile deformation. In southeastern New England sedimentary rocks of late Pennsylvanian age have undergone an amphibolite-facies Barrovian metamorphic event (275–290Ma) that is syn- to post-ductile deformation and is truncated by peraluminous granite. Considerations of patterns of metamorphism in surrounding crystalline rocks implies that at least two distinct late Palaeozoic tectonothermal events have affected New England. In the Piedmont of Virginia and the Carolinas amphibolite-facies metamorphism (roughly 260–310 Ma) is synchronous with the emplacement of syn-kinematic granitoids. In all three areas isogradic patterns, where determinable, are complex, reflecting the effects of later faulting and fault-controlled retrograde metamorphism. In the USA at least, Alleghanian metamorphism also affected areas well beyond the boundaries of Avalonian terranes sensu stricto into the polydeformed crystalline terrane to the W (Inner Piedmont, Merrimack synclinorium). Within these crystalline rocks the Permian thermal overprint appears to be focussed along shear zones. Late Palaeozoic regional metamorphism in the Appalachians probably reflects crustal thickening related to continent-continent or continent-microcontinent collisions characterized by heat transfer along fundamental tectonic boundaries, and not simply proximity to late Palaeozoic igneous activity or subduction-zone tectonics.

Sweet sorghum for ethanol industry for the Piedmont

Approximately one-third of the idle cropland in the Piedmont counties of the five southern states, Virginia, North Carolina, South Carolina, Georgia and Alabama, would have to be planted in sweet sorghum with an average yield of 40 t/ha to produce a volume of ethanol equal tro the volume of petroleum fuel purchased by farmers in the Piedmont counties (518 million L/year), assuming that 65% of the fermentable sugar is extracted. If the by-products are ensiled for cattle feed, it is sufficient to feed 1.5 times the entire cattle population of the Piedmont of Virginia, and 3.0, 0.78, 1.25 and 1.16 times the Piedmont cattle population in North Carolina, South Carolina, Georgia and Alabama, respectively.

Seasonal Changes in Germination Responses of Buried Seeds of Portulaca smallii

BASKIN, J. M., C. C. BASKIN (Sch. Biol. Sci., Univ. Kentucky, Lexington, KY 40506) AND J. F. MCCORMICK (Grad. Prog. Ecol., Univ. Tennessee Knoxville, TN 37916). Seasonal changes in germination responses of buried seeds of Portulaca smallii. Bull. Torrey Bot. Club 1 14:169172. 1987.-Portulaca smallii P. Wilson is a succulent, summer annual endemic to granite outcrops of the Piedmont of Virginia, North Carolina and Georgia. Freshly matured seeds were buried in pots of outcrop soil in mid October 1981 and exposed to natural seasonal temperature cycles. Beginning on November 1, seeds were exhumed at monthly intervals for 28.5 months and tested in light and darkness at thermoperiods of 15/6, 20/10, 25/15, 30/15 and 35/20?C. Seeds were dormant at maturity but became completely nondormant by May 1982. Nondormant seeds required light and a temperature regime > 1 5/6?C to germinate. After seeds lost their initial dormancy, they retained the capacity to germinate to 65-100% in light at 35/20 and 30/ 1 5?C throughout the remainder of the study, which ended in March 1984. In September 1982 and September and October 1983, germination at 25/15?C declined to 38, 19 and 35%, respectively, but by November and December seeds had regained the ability to germinate to 7398%. Seeds germinated at 20/10?C only in April-July 1982 and February-April 1983. The species belongs to the category of summer annuals in which the buried seeds do not re-enter dormancy in spring. Thus, seeds potentially can germinate throughout the growing season.

Effects of site preparation on nitrogen dynamics in the southern Piedmont

The impact of three mechanical site preparation treatments, chop-burn, shear-disc, and shear-pile-disc, on nitrogen dynamics was examined on gauged watersheds in the Piedmont of Virginia. Samples from soil solution and streamwater and a series of soil incubations, both laboratory and in situ, were used to monitor changes in the treatment areas following site preparation. Available nitrogen reserves were lowest in the shear-pile-disc watershed where the logging slash had been piled into windrows. Larger nitrogen reserves were found in the shear-disc and the chop-burn watersheds. Nitrogen mineralization was greater in the site prepared areas than in the uncut stand and mineralization generally increased as site preparation intensity increased. Between 58 and 95 kg/ha of nitrogen were mineralized in the site prepared areas during the first year following treatment compared to only 38 kg/ha during the same period in the uncut stand. Streamwater nitrogen export increased following site preparation with the largest losses of nitrogen occurring in the shear-pile-disc watershed.

Effects of Pine Conversion on Food Plants of Northern Bobwhite Quail, Eastern Wild Turkey, and White-Tailed Deer in the Virginia Piedmont

Abstract Vegetation surveys were conducted in a series of upland stands to discern changes in the abundance of food plants for northern bobwhite quail, eastern wild turkey, and white-tailed deer following conversion from 2nd-growth hardwood and pine-hardwood forest to loblolly pine plantations in the central Piedmont of Virginia. Cover of principal food plants in second-growth native forests was negligible, but mast-producing capability was more than adequate for good deer and turkey habitat. Upon conversion there was a rapid increase in available food plants, but a loss of mast. Cover of principal food plants for bobwhite quail and wild turkey was highest in 1-yr-old plantations; by 3 yr, plantations were deficient in seed-producing plants for these species. Deer browse was adequate in plantations up to 9 yr, but declined rapidly following crown closure at 10-15 yr. Between crown closure and the first commercial thinning (about 20 yr), plantations were of negligible food value to the three wildlife species. Results suggest that optimum conditions for bobwhite are provided by a preponderance of young plantations while those for deer and turkey are supplied by a mix of second-growth forests and various-aged pine plantations.

Effects of Loblolly Pine Plantations on Songbird Dynamics in the Virginia Piedmont

Avifauna was sampled in 8 developmental stages of loblolly pine (Pinus taeda) plantations and in 2nd growth pine-hardwood forests during the summer, winter, and spring seasons of 1979-80 in the central Piedmont of Virginia. During summer, the number of birds (N) peaked in the 2and 5-year-old plantations and dropped significantly (P < 0.05) in older plantations. Average N of species/stand (S), total N of species in all stands of a given developmental stage (T), and species diversity (H') followed a similar trend. N, S, and T were significantly (P < 0.05) lower in the 2nd growth forests than in younger plantations. N, S, T, and H' were lower in winter than in other seasons sampled. N, S, and H' values were higher in the 2-5-year-old pine plantations than in the older, 7-24-year-old plantations. Values for 2nd growth forests were comparable to those in the 7-24-year-old plantations. In the spring breeding season, N, S, T, and H' were similar to those found during the later summer period. Species equitability (J') remained relatively high in all stands surveyed. J. WILDL. MANAGE. 50(3):406-413 Loblolly pine is one of the major tree species used by the forest industry in Virginia. Although not native to the study area in the central Piedmont, it was introduced in the early 1930's and has proved more profitable than the native pines (Williston and Huckenpahler 1958, Smally and Pierce 1972). Abandoned farmlands were used as plantation sites until the mid-1950's when this type of land increased in value. Forest industries then were compelled to use lower value, 2nd growth hardwood stands for plantation sites by clearcutting and planting loblolly pine. This conversion practice has created major changes in the composition and structure of the vegetation found in the central Piedmont (Felix et al. 1983) and may have effects on nongame wildlife species. The objective of this study was to determine the effects of establishment and development of loblolly pine plantations on the relative density, abundance, and diversity of breeding and winter resident songbirds. We would like to acknowledge P. T. Bromley and J. D. Fraser for their reviews of earlier drafts of this paper.

Seismicity, seismic reflection, gravity, and geology of the central Virginia seismic zone: Part 3. Gravity

Bouguer gravity anomalies at 1,870 locations on the central Piedmont of Virginia from 37°37′N to 37°52′N and 77°44′W to 78°23′W display patterns of variation produced by upper-crustal density contrasts and thickening of the crust in a west-northwest direction. No other deep sources are evident. Upper-crustal density contrasts are associated with rock units known from geologic mapping. The subsurface distribution of these rock units, interpreted from seismic-reflection data, was confirmed by measured variations in gravity. A two-dimensional model analysis indicates the following average in situ density values for the principal formations: Arvonia Formation, 2.77 gm/cc; Columbia Granite, 2.75 gm/cc (tonalite) and 2.73 gm/cc (pegmatite); Chopawamsic volcanics, 2.77 gm/cc (felsic units) and 2.79 gm/cc (malic units); Catoctin/Lynchburg/Evington, 2.82 gm/cc; Maidens Gneiss, 2.78 gm/cc; and Grenville Basement, 2.71 gm/cc. Gravity anomalies are consistent with the existence of a major thrust fault, at depths between 9 km and 16 km, that probably separates Grenville Basement rocks from younger, Catoctin/Lynchburg rocks. These anomalies confirm that the slight eastward dip of this thrust fault beneath the western part of the area increases significantly east of 78°05′W.

Succession in Loblolly Pine Plantations Converted from Second-growth Forest in the Central Piedmont of Virginia

Vegetation composition and structure were quantified in 21 pine stands converted from second-growth hardwood-pine forest at two state forests in Virginia. These stands included three replications each of seven developmental stages ranging in age from 1-22 years. Species richness and vegetation cover in the ground stratum showed the same trend: high values in stands 1-5 years of age followed by a decline from 5-15 years, at which point canopy closure was complete, and these variables were relatively stable for the next 7 years. A peak in transgressive stratum richness in the 9th year was followed by a similar decline and leveling off. Evenness (J') values over time were nearly constant for these understory strata, except in 3-year-old stands where a decline in ground stratum evenness occurred due to dominance by Andropogon virginicus. Increasing richness and evenness in the overstory stratum was due to growth of hardwoods. Trends in richness and evenness differed from the old-field successional model due to a high diversity of seeds and sprouts at the start of succession. Despite such differences, the seral stages typical of old-field succession were discernible in converted stand succession. However, they were somewhat abbreviated and masked by the abundance and variety of reproductive units and the rapid closure of the canopy by codeveloping pines and sprout hardwoods. INTRODUCTION The central Piedmont of Virginia is part of the Oak-Pine Forest Region delineated by Braun (1950). Young forests are characteristically dominated by Pinus virginiana and P. echinata and are gradually replaced during succession by an oak-hickory complex (Braun, 1950). From the 1700s to the early 1800s Piedmont lands were cleared, intensively farmed and abandoned (Gottmann, 1969). Abusive crop farming depleted soils and led to severe and extensive topsoil erosion (Culbertson, 1948; Gottmann, 1969). Much abandoned cropland reverted to native forest through succession. The end of the 19th century marked the beginning of a new period of deforestation when most of the commercially valuable forest of the Piedmont was harvested (Gottmann, 1969). Pinus taeda (loblolly pine) has been the principal species planted in the central Piedmont since the 1930s, even though it is incapable of natural regeneration throughout much of this region (S. F. Warner, pers. comm.). Up to the mid-1950s, most planting of P. taeda was in old fields. Owing to a decline in agricultural land abandonment, hardwood and pine-hardwood forests have been directly converted to P. taeda plantations at an accelerated rate. Whereas much is known about the vegetation dynamics of old-field succession in the Piedmont region of the Southeast (Crafton and Wells, 1934; Billings, 1938; McQuilkin, 1940; Oosting, 1942; Keever, 1950; Nicholson and Monk, 1974, 1975), little is known about such changes associated with the establishment and development of pine plantations on sites converted from second-growth forests. Thus, the objective of this study was to examine temporal changes in the composition and structure of vegetation in loblolly pine stands converted from such forests. 1 Present address: 435 Jackson Street, Fall River, Massachusetts 02721. 2 Present address: Department of Biology. 3Department of Biology.

Life histories of some filter-feeding Trichoptera in Virginia

Life histories were determined for seven species of filter-feeding Trichoptera at two sites on the impounded North Anna River and at two sites on the free-flowing South Anna River in the Piedmont of Virginia, U.S.A. Hydropsyche incommoda, H. sparna, and H. venularis were trivoltine at at least three of the four sites, with fast-growing spring and summer generations that matured in June and July, and August and September, respectively, and a slow-growing winter generation that matured in March, April, and May. Cheumatopsyche parentum, Macronema zebratum, Chimarra moselyi, and C. obscura were bivoltine at all sites. The summer generations of these species grew quickly, maturing in June and July, and the winter generation grew slowly, maturing in April and May. Instars I–V, pupae, and adults of most species were present continually from April through October. All species overwintered in instars III–V, and in most species instar II was present during the winter also. Comparisons of Hydropsyche life histories in the Anna Rivers with those reported from other eastern North America rivers reveal that differences in voltinism are probably due to a complex interaction of food quality and temperature regime.