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71.
TEKLE K 《Environmental management》1999,23(4):419-427
/ Understanding the problems of land degradation and seeking long-lasting solutions to these problems should be one of the central concerns of countries such as Ethiopia where agriculture is the mainstay of no less than 85% of the population. To this end, the collaboration of policy makers, researchers, donor agencies, and the local people is indispensable. In this paper an attempt is made to discuss the causes of land degradation and the reasons for the failure in the endeavors made to solve the problems. Possible solutions, which may help to ameliorate the situation, are also suggested. The study deals with South Wello (a region in northern Ethiopia), but the assessment is, by and large, a reflection of most of the highlands in the country. KEY WORDS: Agroforestry; Donor agencies; Food for work; Hillside closures; Land rehabilitation; Local participation; Population growth; Reforestation 相似文献
72.
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
73.
There is abundant evidence that many factors can influence the toxicity of a particular pollutant including environmental fluctuations, season of the year, stage in life cycle, size, and sex. All of these factors should be assessed before making a judgment of the effect on natural populations. Such an assessment can be conceptualized using a simple population model through whichcontrol gates operate as functions of 1). the direct self-maintainance feedback from existing adult population biomass and 2). the recruitment of new individuals due to the maturation of larvae. By extracting general principles of organismic response to pollutants it is possible to incorporate the information into large-scale ecosystem models which would serve as working tools for answering environmental decision-making problems. 相似文献
74.
California and other regions in the United States are becoming more populated and ethnically diverse, and thus, ecological
impacts on the wildland–urban interface are a significant policy concern. In a socioeconomic assessment focused on the geographic
regions surrounding four national forests in southern California, population projections are being formulated to assist in
the update of forest plans. In southern California, the projected trend of explosive population growth combined with increased
ethnic and racial diversity indicates four challenges for environmental management. First, patterns of recreation use on wildlands
are likely to change, and management of these areas will have to address new needs. Second, as land-management agencies face
changing constituencies, new methods of soliciting public involvement from ethnic and racial groups will be necessary. Third,
growth in the region is likely to encroach upon wildland areas, affecting water, air, open space, and endangered species.
Fourth, in order to address all these concerns in a climate of declining budgets, resource management agencies need to strengthen
collaborative relationships with other agencies in the region. How environmental managers approach these changes has widespread
implications for the ecological sustainability of forests in southern California. 相似文献
75.
Spermophilus townsendii ) prey. These changes could occur directly or as a result of changes in the vegetation available as food and cover for the
ground squirrels. We assessed the effects of long-term tracking by armored vehicles by comparing 9-ha areas in sagebrush (Artemisia tridentata) -dominated shrubsteppe and bluegrass (Poa secunda) -dominated grasslands subjected to low-intensity tracking for ∼50 years with others that had not been tracked. We did not
detect any effect on ground squirrel population dynamics associated with long-term tracking. Although densities of adults
and juveniles tended to be higher in the areas exposed to such tracking, we attribute this difference to other factors that
varied spatially. To determine short-term (two-year) effects, we experimentally tracked two sagebrush and two grassland sites
with an M-1 tank after animals had begun their inactive season. In the following two active seasons we monitored squirrel
demography and behavior and vegetative characteristics on the experimentally tracked sites and compared the results with control
sites. Although we experimentally tracked ∼33% of the surface of each of four sites where ground squirrel densities were assessed,
the tracking had a detectable effect only on some herbaceous perennials and did not influence ground squirrel densities or
behavior significantly during the subsequent two active seasons. We conclude that tracking after the start of the inactive
season is likely to influence ground squirrel demography or behavior only if vegetation cover is substantially changed by
decreasing coverage of preferred food plants or increasing the coverage of annual grasses and forbs that are succulent for
only a short time each year. 相似文献
76.
人口是人口,资源与环境系统中最根本的主导因素,人口增长过快,将直接加大对资源与环境的压力,并影响人口素质的提高,根据我国人口庞大的基数,过快的增长速度,独特的人口结构和较低的文化素质现状,对生态环境造成的压力进行了系统分析,进而提出了控制人口增长,改善生态环境和全面发展国发经济的对策,以保证跨世纪人口,资源,环境呈现协调,持续,健康的发展趋势。 相似文献
77.
I. Zvonova P. Krajewski M. Ammann V. Filistovic B. Kanyar S.L. Simon D. Webbe-Wood 《Journal of environmental radioactivity》2010,101(1):8-10003
Within the project “Environmental Modelling for Radiation Safety” (EMRAS) organized by the IAEA in 2003 experimental data of 131I measurements following the Chernobyl accident in the Plavsk district of Tula region, Russia were used to validate the calculations of some radioecological transfer models. Nine models participated in the inter-comparison. Levels of 137Cs soil contamination in all the settlements and 131I/137Cs isotopic ratios in the depositions in some locations were used as the main input information. 370 measurements of 131I content in thyroid of townspeople and villagers, and 90 measurements of 131I concentration in milk were used for validation of the model predictions.A remarkable improvement in models performance comparing with previous inter-comparison exercise was demonstrated. Predictions of the various models were within a factor of three relative to the observations, discrepancies between the estimates of average doses to thyroid produced by most participant not exceeded a factor of ten. 相似文献
78.
Hanna Eriksson H?gg Steve W. Lyon Teresia W?llstedt Carl-Magnus M?rth Bj?rn Claremar Christoph Humborg 《Ambio》2014,43(3):337-351
Dynamic model simulations of the future climate and projections of future lifestyles within the Baltic Sea Drainage Basin (BSDB) were considered in this study to estimate potential trends in future nutrient loads to the Baltic Sea. Total nitrogen and total phosphorus loads were estimated using a simple proxy based only on human population (to account for nutrient sources) and stream discharges (to account for nutrient transport). This population-discharge proxy provided a good estimate for nutrient loads across the seven sub-basins of the BSDB considered. All climate scenarios considered here produced increased nutrient loads to the Baltic Sea over the next 100 years. There was variation between the climate scenarios such that sub-basin and regional differences were seen in future nutrient runoff depending on the climate model and scenario considered. Regardless, the results of this study indicate that changes in lifestyle brought about through shifts in consumption and population potentially overshadow the climate effects on future nutrient runoff for the entire BSDB. Regionally, however, lifestyle changes appear relatively more important in the southern regions of the BSDB while climatic changes appear more important in the northern regions with regards to future increases in nutrient loads. From a whole-ecosystem management perspective of the BSDB, this implies that implementation of improved and targeted management practices can still bring about improved conditions in the Baltic Sea in the face of a warmer and wetter future climate. 相似文献
79.
At the European level, lacertid lizards have been proposed as potential model species for reptile ecotoxicology. We studied demographic and morphological aspects of natural field subpopulations of Podarcis bocagei inhabiting similar agricultural habitats which were either regularly exposed to pesticides, or not. Parameters examined in this study included population size and density, sex ratio, adult body size, fluctuating asymmetry in femoral pores and parasite prevalence. In general, we detected few statistically significant differences between the exposed and reference subpopulations. Although field situations are ecologically complex and factors other than pesticides may be acting, the absence of observable effects on field subpopulations is probably indicative that lizards are coping or compensating for this level of exposure. 相似文献
80.
本文从灾害学的角度提出了人口过多或增长过快也是一种灾害,这种灾害与所有的自然灾害和人文灾害密切相关,是许多灾害的诱发因素。 相似文献