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601.
LARS A. BRUDVIG§ CATHERINE M. MABRY JAMES R. MILLER† TRACY A. WALKER‡ 《Conservation biology》2007,21(3):864-874
Abstract: Reintroduction of fire and grazing, alone or in combination, has increasingly been recognized as central to the restoration of North American mixed-grass and tallgrass prairies. Although ecological studies of these systems are abundant, they have generally been observational, or if experimental, have focused on plant species diversity. Species diversity measures alone are not sufficient to inform management, which often has goals associated with life-form groups and individual species. We examined the effects of prescribed fire, light cattle grazing, and a combination of fire and grazing on three vegetation components: species diversity, groups of species categorized by life-form, and individual species. We evaluated how successful these three treatments were in achieving specific management goals for prairies in the Iowa Loess Hills (U.S.A.). The grazing treatment promoted the greatest overall species richness, whereas grazing and burning and grazing treatments resulted in the lowest cover by woody species. Burning alone best achieved the management goals of increasing the cover and diversity of native species and reducing exotic forb and (predominantly exotic) cool-season grass cover. Species-specific responses to treatments appeared idiosyncratic (i.e., within each treatment there existed a set of species attaining their highest frequency) and nearly half of uncommon species were present in only one treatment. Because all management goals were not achieved by any one treatment, we conclude that management in this region may need refining. We suggest that a mosaic of burning and grazing (alone and in combination) may provide the greatest landscape-level species richness; however, this strategy would also likely promote the persistence of exotic species. Our results support the need to consider multiple measures, including species-specific responses, when planning and evaluating management . 相似文献
602.
A. Yu. Kudryavtsev 《Russian Journal of Ecology》2007,38(5):299-305
The current dynamics of ecosystems of the forest-steppe system is most adequately described via determining the probable trajectories of changes in its elements in a simple Markov chain. The obtained data have made it possible to determine the direction of succession and draw its scheme. Theoretically possible series of community development are presented. The succession of community restoration from the spread of shrubs over steppificated fallow lands to the formation of low forests of European bird cherry has been analyzed. The restoration cycle of ecosystem dynamics is described by eight age stages. 相似文献
603.
S. Hellsten U. Dragosits C. J. Place T. H. Misselbrook Y. S. Tang M. A. Sutton 《Water, Air, & Soil Pollution: Focus》2007,7(1-3):3-13
Most ammonia (NH3) emission inventories have been calculated on an annual basis and do not take into account the seasonal variability of emissions
that occur as a consequence of climate and agricultural practices that change throughout the year. When used as input to atmospheric
transport models to simulate concentration fields, these models therefore fail to capture seasonal variations in ammonia concentration
and dry and wet deposition. In this study, seasonal NH3 emissions from agriculture were modelled on a monthly basis for the year 2000, by incorporating temporal aspects of farming
practice. These monthly emissions were then spatially distributed using the AENEID model (Atmospheric Emissions for National
Environmental Impacts Determination). The monthly model took the temporal variation in the magnitude of the ammonia emissions,
as well as the fine scale (1-km) spatial variation of those temporal changes into account to provide improved outputs at 5-km
resolution. The resulting NH3 emission maps showed a strong seasonal emission pattern, with the highest emissions during springtime (March and April) and
the lowest emissions during summer (May to July). This emission pattern was mainly influenced by whether cattle were outside
grazing or housed and by the application of manures and fertilizers to the land. When the modelled emissions were compared
with measured NH3 concentrations, the comparison suggested that the modelled emission trend corresponds fairly well with the seasonal trend
in the measurements. The remaining discrepancies point to the need to develop functional parametrisations of the interactions
with climatic seasonal variation. 相似文献
604.
605.
BURGER J 《Environmental management》2000,26(5):469-478
With the ending of the Cold War, several federal agencies are reclaiming land through remediation and restoration and are
considering potential future land uses that are compatible with current uses and local needs. Some sites are sufficiently
contaminated that it is likely that the responsible federal agency will retain control over the land for the foreseeable future,
providing them with a stewardship mission. This is particularly true of some of the larger Department of Energy (DOE) facilities
contaminated during the production of nuclear weapons. The use of the term “restoration” is explored in this paper because
the word means different things to the public, ecologists, and environmental managers responsible for contaminated sites,
such as Superfund sites and the DOE facilities. While environmental restoration usually refers to remediation and removal
of hazardous wastes, ecological restoration refers to the broader process of repairing damaged ecosystems and enhancing their
productivity and/or biodiversity. The goals of the two types of restoration can be melded by considering environmental restoration
as a special case of ecological restoration, one that involves risk reduction from hazardous wastes, and by broadening environmental
restoration to include a more extensive problem-formulation phase (both temporal and spatial), which includes the goal of
reestablishing a functioning ecosystem after remediation. Further, evaluating options for the desired post remediation result
will inform managers and policy-makers concerning the feasibility and efficacy of environmental restoration itself. 相似文献
606.
/ Fishes and their habitats were sampled in Harland Creek, Mississippi, for 3 years to compare the relative value of three types of bank treatment in an incised, warmwater stream. Semiannual samples were collected from 10 reaches: 3 reaches protected by each of the three types of protection (longitudinal stone toe, stone spurs, and dormant willow posts) and an unprotected, slowly eroding bend. Protection of concave banks of bends had no measurable effect on the habitat quality of downstream riffles. Although bends and adjacent downstream riffles were faunistically similar at the species level, catostomids and centrarchids were more dominant in pools and smaller cyprinids more dominant in riffles. Reaches with willow posts were slightly deeper than the others, most likely because of geomorphic factors rather than bank treatment. Mean water surface widths in reaches stabilized with stone spurs were 40% to 90% greater than for other treatments, and current velocities were greatest in reaches with stone toe. Patterns of fish abundance and species diversity did not differ significantly among treatments. However, principal components analysis indicated that the fish species distribution associated with the untreated reference site was distinct. Reaches stabilized with stone spurs supported significantly higher densities of large fish and higher levels of fish biomass per unit channel length than reaches with other bank treatments, generally confirming previous research in the region. Initial costs for spurs were comparable to those for stone toe and about three times greater than for willow posts. 相似文献
607.
608.
John Cobourn 《Journal of the American Water Resources Association》2006,42(1):35-43
Riparian ecosystems are designated for special protection from development and disturbance at Lake Tahoe. The Tahoe Regional Planning Agency (TRPA) required protection of Stream Environment Zones (SEZs) in its Regional Plan for the Lake Tahoe Basin in 1987. These zones are identified by the presence of key indicators such as the evidence of surface water flow, riparian vegetation, near‐surface ground water, designated floodplain, and alluvial soils. They are mapped on each potential building site and assigned a setback that is also off limits to building construction. The SEZs are protected to maintain their functions and values, including flood attenuation, water quality enhancement, and wildlife habitat. Strict regulations control use or disturbance of SEZs on public and private property throughout the watershed. The TRPA has set restoration targets to increase the acreage of naturally functioning SEZs in the Tahoe Basin. Many SEZ restoration projects have been designed and implemented, but SEZ restoration targets have not been met. More SEZ restoration projects are being designed and funded each year. Restoration designers would benefit from increased effectiveness monitoring of completed projects and Web‐based dissemination of monitoring results. 相似文献
609.
There has been much literature on ecological model of Prisoner's Dilemma (PD) game. This game illustrates that cooperation can evolve in situations where individuals tend to look after themselves. In order to explain some behaviors of altruism in animal societies, the strategy All Cooperate (AC), often called the Golden Rule, is more appropriate than other strategies. However, very little is known about the superiority of AC. In the present article, we study patch dynamics based on non-iterated PD game, applying two different methods: island and lattice models. Each patch is assumed to be either vacant or composed of a population of AC or All Defect (AD), where AD means a selfish strategy. Both models exhibit a phase transition between a phase where both AC and AD survive, and a phase where AD is extinct. The latter phase means that AC beats AD completely. In the case of lattice model, the extinction of AD easily occurs and the abundance of AC takes a larger value, compared with the island model. Our models can be also extended to general iterated PD game; we describe the reason why AC can outperform any other strategy. 相似文献
610.
M. Ketzel P. Louka P. Sahm E. Guilloteau J.-F. Sini N. Moussiopoulos 《Water, Air, & Soil Pollution: Focus》2002,2(5-6):603-613
Microscale computational fluid dynamics (CFD) modelsdeveloped in different European countries were applied towell defined test cases comprising a variety of 2 and 3dimensional configurations for which measurements from windtunnel or field studies were available. This paper presentsthe results of five CFD codes employing the widely used`standard k--model' (CHENSI, CHENSI-2, MIMO, MISKAM, TASCflow) for a street canyon in Hannover, Germany(Göttinger Strasse). Firstly the characteristics of theflow field predicted by the different codes are comparedwith high spatial resolution wind tunnel measurements;secondly the calculated concentration fields are comparedwith field and wind tunnel data. Both agreements (e.g. forthe general flow and concentration fields) anddisagreements (e.g. for the level of concentration) areobserved in the comparison. The discussion aims atexplaining the differences along with giving somesuggestions to CFD model users on how to calculate suchcomplex flows, but also to experimentalists on whereconcentration measurements should be taken in order to bemore representative for a whole street and to avoiddistinct local effects. 相似文献