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291.
To better understand the role of herbivory and fire as potential disturbance processes in sagebrush communities, we examined
responses of a grazing ungulate, elk (Cervus elaphus), following prescribed burning of sagebrush (Artemisia
tridentata ssp. vaseyana) in south-central Montana (USA.) with concurrent monitoring of changes in plant production, nutritional quality, and community
diversity from 1989–1999. Burning transformed low-diversity, sagebrush-dominated communities into high-diversity, graminoid-forb
communities that persisted for 10 years without significant reestablishment of sagebrush. Elk increased use of burned sites
one year after burning, but elk use returned to pre-burn levels over the next two to nine years. Forage biomass and nutritional
quality declined after initial increases that coincided with increased elk use. Increases in elk use appeared to be influenced
by increases in combined graminoid and forb production and changes in structural vegetation characteristics that permitted
greater foraging efficiency. Declines in use were associated with loss of nutritional enhancement and declines in combined
graminoid and forb production. Managers may observe only short-term responses from grazing ungulates to prescribed fire in
sagebrush communities, but can expect longer-term increases in plant diversity and establishment of graminoid-forb communities. 相似文献
292.
Tamim Younos Fred W. Kaurish Terri Brown Raymond de Leon 《Journal of the American Water Resources Association》2001,37(2):327-334
ABSTRACT: Karst terrane provides a linkage between surface water and ground water regimes by means of caves, sinkholes and swallets, and sinking streams, and facilitates the inter‐watershed transfer of water and contaminants through these subsurface systems. The goal of this study was to develop procedures to identify the sources of degradation of a creek situated in a complex karst‐water system. The study approach consisted of using dye tracing technique to determine subsurface flow paths through the karst system, a water‐sampling network to identify and characterize pollution sources within the surface watershed and subsurface flow regime, and evaluation of analytical data for several water quality parameters. The results of this study provide an interesting perspective of water and contaminant movement in karst‐water systems and pinpoint the sources of stream contamination for a case study site in southwest Virginia where two springs supply water to a contaminated freshwater stream. 相似文献
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Fred E. Parady III 《Environmental geochemistry and health》1984,7(1):26-27
Bridger Coal Company operates a 5.8 million tpy surface coal mine thrity five miles northeast of Rock Springs. Wyoming. Approximately 20.000 acres are under permit, with disturbance over the life of the mine projected to reach 10,000 acres. Located on the western rim of the continental divide, the mine receives less than 8.5 inches of precipitation annually. Soils in the area are coarse-textured. and problems associated with elevated salinity and sodicity arc encountered.A variety of common reclamation techniques have been modified to reflect these conditions. Soil horizons are segregated during salvage operations (the surface six inches as topsoil and the balance as subsoil). Unsuitable materials are not salvaged. Direct application of soil is used (over 130 acres in 1983) to maximize native plant regeneration and conserve soil fertility. Inter-seeding of seeding failures has proven to be significantly more successful than chisel plowing and reseeding. Broadcast seeding has been ineffective because of strong winds, and a no till drill has been modified to handle diverse seed mixes and rock conditions. The utility of fertilization under typically xeric moisture regimes is being evaluated. A research project has been initiated to assess establishment of a predominately native, diverse seed mix under irrigation, as well as to determine irrigation rates and duration. 相似文献
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R. Fred Rolsten 《Journal of the Air & Waste Management Association (1995)》2013,63(7):681-683
Annually about 100 million automobiles suck in vast quantities of air and eject it in a contaminated state. When, pollutants are measured by weight,1 it seems that the automobile is the nation’s worst polluter. The EPA estimates that in 1969 motor vehicles accounted for 98 million tons of CO, 8.7 million tons of NOx and more than 17 million tons of HC. 相似文献
299.
Fred J. Van Staden 《Journal of environmental psychology》1984,4(2):97-118
This interview study focused on urban early adolescents' conscious experiences of high density conditions. Thirty children residing in apartments in two boroughs of New York City (Brooklyn and Manhattan), participated in this study. Control variables included income level, age, family constellation, and length of residence. Sex, apartment density, building size and neighbourhood density served as classification variables. The interview lasted approximately forty minutes and addressed the following issues.Personal conceptualizations and definitions of crowding.Evaluation of the children's perceived neighbourhood.Peer relationships.Perceived social and physical opportunities and constraints.Interviews were tape recorded, transcribed and content analyzed.The children's conceptualizations of crowding emphasized large numbers of people, spatial restriction and an aversive experience of the situation as relevant components of the crowding construct. The restriction of behavioural choice as it relates to goal postponement and the child's efforts to come to terms with larger organizational social structures, underlined the interpretation of crowding as a socio-physical stressor. While information overload was depicted as another relevant characteristic of crowding situations, its aversive experience was mediated by the presence of known others. Even though this diversity on social and physical levels was often experienced as stressful, it was also positively viewed in situations where interpersonal contact or a sense of familiarity were not overriden by other situation demands.Boys tended to spend more time in their neighbourhood engaged in a broader range of activities than girls. In this sample, boys also took less part in structured group activities and rated their neighbourhoods somewhat more positively than girls. Girls experienced less freedom and more social restrictions in exploring and actively interacting with their extended surroundings than boys.The issues of movement and situationally imposed behavioural restriction were central themes in children's conscious experiences of high density situations. Emphasis was placed on physiological arousal linked to the perception of aversive social qualities of high density situations. It appears that an increase in the need to act out is more a function of the child's awareness of having to conform to external norms, or experiencing a loss of perceived social control in situations where vigilance is required, than a clear cognisance of spatial restrictions.The investigation of the impact of high density conditions on the child's sociocognitive development and identity formation is viewed as potentially fruitful directions for future research. 相似文献
300.