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41.
Should heterogeneity be the basis for conservation? Grassland bird response to fire and grazing. 总被引:2,自引:0,他引:2
Samuel D Fuhlendorf Wade C Harrell David M Engle Robert G Hamilton Craig A Davis David M Leslie 《Ecological applications》2006,16(5):1706-1716
In tallgrass prairie, disturbances such as grazing and fire can generate patchiness across the landscape, contributing to a shifting mosaic that presumably enhances biodiversity. Grassland birds evolved within the context of this shifting mosaic, with some species restricted to one or two patch types created under spatially and temporally distinct disturbance regimes. Thus, management-driven reductions in heterogeneity may be partly responsible for declines in numbers of grassland birds. We experimentally altered spatial heterogeneity of vegetation structure within a tallgrass prairie by varying the spatial and temporal extent of fire and by allowing grazing animals to move freely among burned and unburned patches (patch treatment). We contrasted this disturbance regime with traditional agricultural management of the region that promotes homogeneity (traditional treatment). We monitored grassland bird abundance during the breeding seasons of 2001-2003 to determine the influence of altered spatial heterogeneity on the grassland bird community. Focal disturbances of patch burning and grazing that shifted through the landscape over several years resulted in a more heterogeneous pattern of vegetation than uniform application of fire and grazing. Greater spatial heterogeneity in vegetation provided greater variability in the grassland bird community. Some bird species occurred in greatest abundance within focally disturbed patches, while others occurred in relatively undisturbed patches in our patch treatment. Henslow's Sparrow, a declining species, occurred only within the patch treatment. Upland Sandpiper and some other species were more abundant on recently disturbed patches within the same treatment. The patch burn treatment created the entire gradient of vegetation structure required to maintain a suite of grassland bird species that differ in habitat preferences. Our study demonstrated that increasing spatial and temporal heterogeneity of disturbance in grasslands increases variability in vegetation structure that results in greater variability at higher trophic levels. Thus, management that creates a shifting mosaic using spatially and temporally discrete disturbances in grasslands can be a useful tool in conservation. In the case of North American tallgrass prairie, discrete fires that capitalize on preferential grazing behavior of large ungulates promote a shifting mosaic of habitat types that maintain biodiversity and agricultural productivity. 相似文献
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Chencho Norbu Prof. Timothy J. Downs Edward Yeboah Dr. L.J.R. Scholtens Dr. Jyotsna Bapat Maren Oelbermann Ph.D. Sayyed Ahang Kowsar Jaime Alexandra Webbe Bram Govaerts Ph.D. Nele Verhulst M. Sc. Goodspeed Kopolo Maria Rosário Partidário Mr. N’guessan Alphonse Kouassi John All Ph.D. JD Narcisa Pricope Leslie Lipper 《Natural resources forum》2008,32(3):252-256
46.
This article describes and tests a systems theory-based policy indicators model. The framework is used to examine propositions
about linkages between states' ecological-spatial characteristics and subsequent selected solid waste management (SWM) -related
environmental policies. It was hypothesized that state characteristics of: (1) population density (used as a garbage-per-land
area index), (2) population convergence within urban areas, and (3) percent population change in the interval 1980–1985, could
jointly explain state variation in both the number and the vigor of SWM policy outputs. Greater levels of spatial pressure
were proposed to be related directly to more numerous, more convincing policies. Proposals are grounded in the literature
of organizational search theory, crisis stimulation, and technological pressure.
Results revealed that the sociospatial model in fact could explain a reasonable proportion of policy variation across states.
However, not all hypotheses are supported. Population change shows an indirect, rather than the anticipated direct, relationship
with policy output levels. In addition, when used in the model as a pollution intensity index, population density failed to
contribute significantly to an explanation of differences in state SWM policy levels. The analysis raises questions about
changes occurring over time in the nature and direction of linkages between sociospatial measures and policy responses. This
study suggests that strengthening policy indicator models may require questioning key assumptions and theoretical bases, conducting
longitudinal studies, and factoring in political, economic, and other policy environment forces. 相似文献
47.
Remediation of streams impacted by non-point source contaminants requires an understanding of both the areas within a watershed that are contributing contamination to streams and the pathways of contaminant migration to streams. From 1998 to 2002, we studied the migration of 90Sr in the Borschi watershed, a small (8.5 km2) catchment three km south of the Chernobyl Nuclear Power Plant, Ukraine. Fuel particles, distributed in a heterogeneous pattern across the watershed, are weathering and releasing 90Sr from the fuel matrix. Depletion of (90)Sr, evaluated in comparison to the immobile fission product europium-154, is occurring in the channel and wetland sediment. Channel sediments are uniformly depleted in 90Sr with depth. In wetland sediments, there is a zone of depletion in the top 10 cm and a zone of accumulation at depths from 10 to 25 cm. Estimates of 90Sr depletion are used to map the effective source area that has contributed (90)Sr loading to the main channel. The effective source area includes channel bottom sediments, a wetland in the central region of the watershed, and periodically flooded soils surrounding the wetland. The total depletion from the effective source area is estimated to be 36 +/- 7 x 10(10) Bq. Based on observations of stream flow rate and water quality in 1999-2001, the annual 90Sr removal rate from the watershed is estimated to be 1.4 +/-0.2 x 10(10) or 1.5% of the inventory per year. When extrapolated over a 15-year period following the Chernobyl accident, the last value is in reasonable agreement with the estimated depletion of the source area based on 90Sr/154Eu ratios. The 90Sr yearly leaching rate considering the whole watershed is 0.2% while the 90Sr leaching rate considering the effective source area is an order of magnitude higher. Most of the 90Sr release in the watershed has originated from an effective source area of 0.62 km2, or 7% of the watershed area. 相似文献
48.
Patricia Bobrow Barbara Gaige Glenn Harris Joyce Kennedy Leslie King William Raymond Darrin Werbitsky 《Environmental management》1984,8(1):45-53
This study compares the effectiveness of two regional planning agencies in terms of public support for various planning activities. The Adirondack Park Agency and the Temporary State Commission on Tug Hill have fundamentally different approaches to planning. The Adirondack Park Agency has implemented a restrictive regulatory program with little citizen participation by Adirondack residents. The Tug Hill Commission has implemented an advisory and coordinating program with an emphasis on public input. Residents of two towns in each region were surveyed to determine environmental concern and support for regional planning activities. Respondents from both regions favored a planning agency that incorporates citizen input; controls air, water, and toxic waste pollution; and develops recreation areas. They strongly opposed an agency that regulates private land-use. Basic demographic characteristics and levels of environmental concern were similar in all four towns, but receptivity to various planning activities was consistently greater among residents of the Tug Hill Region. Paired comparisons of the four towns demonstrated no differences between towns of the same region and significant differences between towns of different regions. Public support for regional planning is greater in the Tug Hill Region than in the Adirondack Park. 相似文献
49.
Many small communities are concerned about health effects from environmental pollutants. One such community, Orwell, in Oswego County, New York, was investigated to determine if the level of cancer was significantly high in comparison to the county and the state. A pilot health study was administered among residents living in a defined area. Results of the survey demonstrated that cancer incidence was higher than both Oswego County and New York State, while cancer mortality was higher for men and lower for woman. A closer examination of the data showed that the way in which health surveys are usually analyzed may not be appropriate for small communities. In particular, some parametric statistics, such as chi-square analysis, might show significant differences between populations when standardized incidence and mortality rates are derived from small samples, yet standard deviations calculated from these data are so large as to cast doubt on the analysis. Researchers have discussed this problem theoretically, but empirical studies illustrating the difficulties have not heretofore appeared in the published literature. For health studies in small communities, greater consideration should be given to risk ratios and the implications of standard deviations. 相似文献
50.
Le Guet Thibaut Hsini Ilham Labanowski Jérôme Mondamert Leslie 《Environmental science and pollution research international》2018,25(15):14532-14543
Environmental Science and Pollution Research - Sorption of pharmaceuticals onto sediments is frequently related to organic matter content. Thus, the present work aimed to compare the effect of... 相似文献