Assessment of frequent cutting as a plant-community management technique in power-line corridors

Repeated cutting of vegetation at or near ground level in power-line corridors is a common practice for inhibiting tree growth and regeneration. However, few data exist on long-term community responses. In this study, we sampled 20 northern Kentucky power-line corridors and compared their seedling and sapling communities to the edges and interiors of adjacent undisturbed forests. Mean seedling and sapling density in corridors was roughly twice that of adjacent undisturbed forest interiors, suggesting that repeated cutting is not a viable method of inhibiting tree regeneration. Corridor communities were dominated byRobinia pseudoacacia (black locust) andFraxinus americana (white ash), but ordinations indicated strong similaritties among communities in corridors and adjacent forests. Many of the tree species found in adjacent forests, with the exception of a few shade-tolerant species, had highest seedling and sapling densities in corridors. Stump or root sprouting by many species appears to regenerate forests quickly after cutting. However, disturbed soil and detritus accumulations caused by management crews and their equipment may also create a large variety of microsites for seedling establishment. Because repeated cutting selects for dominance by species with highest sprout growth rates, it should not be used as the sole management technique. It may instead be used to alter the vigor, stature, and stored reserves of trees so that herbicides or other methods of tree control can be used more efficiently.     

THE PLIGHT OF THE URBAN RESERVOIR: A CASE STUDY1

ABSTRACT: This paper details the increasing tendency to overdevelop lands adjacent to public reservoirs. The impact on water quality of the pollutant load carried in surface runoff from developed lands is described as well as the depreciation in recreational experience due to loss of scenic horizons. The case study, Spruce Run Reservoir in Clinton, New Jersey, included population and demand projections. Land speculation and proposed development are evaluated on a physical constraint basis. Areas of conflict are outlined and conflict resolutions proposed.     

基于特征和知识的精密注塑模设计和制造系统

采用先进的CAD/CAM技术对传统模具设计制造方法进行改造,是提高模具设计制造质量和效率的关键.此文提出基于特征和知识的才法构造精密注塑模设计和制造系统,并介绍了系统的总体方案和系统包含的各模块功能.这一系统是浙江省科委八五攻关项目“精密注塑模设计和制造(CAD/CAM)技术”的核心.     

C-Lock (Patent Pending): A System for Estimating and Certifying Carbon Emission Reduction Credits for the Sequestration of Soil Carbon on Agricultural Land

The C-Lock system was developed to address the need for an improved method of quantifying and certifying project-level carbon emission reduction credits (CERC). It was designed to enable individual landowners to efficiently quantify, certify, pool, market and trade CERCs generated by agricultural management practices. We provide a general overview of the C-Lock system as it has been implemented for the USA State of South Dakota. C-Lock is comprised of four linked components: a web interface, a client database, a Geographic Information System (GIS) database of soil, climate and generalized land use history parameters, and the CENTURY soil carbon model. The user-friendly interface elicits generalized land-use and crop history information from the client from 1900 through 1989, then explicit annual information from 1990 onward. A climate-zone level landuse and crop management database is used to fill in gaps in the client-provided data. These data are used to drive the CENTURY model, which estimates annual changes in soil carbon stocks. Monte Carlo simulation is used to estimate uncertainty bounds, and these are applied to the CENTURY outputs in order to provide probabilistic estimates of accrued CERCs in a manner that is transparent and verifiable. In a demonstration application, CERCs are estimated for three different land-use scenarios on a representative field in eastern South Dakota: reduced tillage or conservation (no-till) management of a corn (maize)/wheat/soybean rotation, and enrollment in the Conservation Reserve Program, which entails establishing permanent grass cover. The credits are based on a business-asusual scenario of conventional tillage.     

Fluorogenic compound hydrolysis as a measure of toxicity-induced cytoplasmic viscosity and pH changes

If a fluorogenic compound, such as fluorescein diacetate, is added to a water solution containing living cells it becomes hydrolyzed by intracellular esterases into a fluorochrome whose fluorescence can be used to monitor the cytoplasmic pH and the cytoplasmic viscosity of the cells. In this paper we have used this technique to measure the effects of different concentrations of Co2+ and Cd2+ ions on the cytoplasmic pH and the cytoplasmic viscosity of a single cell culture. Our results indicate that the observed decrease in the efficiency of the intracellular hydrolyzation of fluorogenic substances in the presence of different concentrations of heavy metals could be caused by both a decrease in the cytoplasmic pH and an increase in the cytoplasmic viscosity. A decrease in cytoplasmic pH would decrease the effectiveness of the intracellular enzymes, whereas an increase in cytoplasmic viscosity would decrease diffusion which would also reduce the effectiveness of the reaction. The dependence of the reciprocal of the cytoplasmic viscosity on the concentration of these metals correlates well with published results on their toxicity.     

Biochemical composition,energy content and chemical antifeedant and antifoulant defenses of the colonial Antarctic ascidian<Emphasis Type="Italic"> Distaplia cylindrica</Emphasis>

The colonial ascidian Distaplia cylindrica occurs both as scattered individual colonies or in gardens of colonies in fine-grained soft substrata below 20 m depths off Anvers Island along the Antarctic Peninsula. Individual colonies, shaped as tall rod-like cylinders and anchored in the sediments by a bulbous base, may measure up to 7 m in height. D. cylindrica represent a considerable source of materials and energy for prospective predators, as well as potential surface area for fouling organisms. Nonetheless, qualitative in situ observations provided no evidence of predation by sympatric predators such as abundant sea stars, nor obvious biofouling of colony surfaces. Mean energy content of whole-colony tissue of D. cylindrica was relatively high for an ascidian (14.7 kJ g^–1 dry wt), with most of this energy attributable to protein (12.7 kJ g^–1 dry wt). The sympatric omnivorous sea star Odontaster validus consistently rejected pieces of D. cylindrica colonies in laboratory feeding assays, while readily ingesting similarly sized alginate food pellets. Feeding deterrence was determined to be attributable to defensive chemistry, as colonies of D. cylindrica are nutritionally attractive and lack physical protection (conspicuous skeletal elements or a tough outer tunic), and O. validus display significant feeding-deterrent responses to alginate food pellets containing tissue-level concentrations of organic extracts. In addition, high acidity measured on outer colony surfaces (pH 1.5) as well as homogenized whole-colony tissues (pH 2.5) are indicative of surface sequestration of inorganic acids. Agar food pellets prepared at tissue levels of acidity resulted in significant feeding deterrence in sea stars. Thus, both inorganic acids and secondary metabolites contribute to chemical feeding defenses. D. cylindrica also possesses potent antifoulant secondary metabolites. Tissue-level concentrations of hydrophilic and lipophilic extracts caused significant mortality in a sympatric pennate diatom. Chemical feeding deterrents and antifoulants are likely to contribute to the abundance of D. cylindrica and, in turn, play a role in regulating energy transfer and community structure in benthic marine environments surrounding Antarctica.Communicated by P.W. Sammarco, Chauvin