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311.
312.
Land-Cover Change Trajectories in Northern Ghana 总被引:3,自引:0,他引:3
Land-cover change trajectories are an emergent property of complex human–environment systems such as the land-use system.
An understanding of the factors responsible for land change trajectories is fundamental for land-use planning and the development
of land-related policies. The aims of this study were to characterize and identify the spatial determinants of agricultural
land-cover change trajectories in northern Ghana. Land-cover change trajectories were defined using land-cover maps prepared
from Landsat Thematic Mapper dataset acquired in 1984, 1992, and 1999. Binary logistic regression was used to model the probability
of observing the trajectories as a function of spatially explicit biophysical and socioeconomic independent variables. Population
densities generally increased along the continuum of land-use intensity, whereas distance from market and roads generally
decreased along this continuum. Apparently, roads and market serve as incentives for settlement and agricultural land use.
An increase in population density is an important spatial determinant only for trajectories where the dominant change process
is agricultural extensification. A major response to population growth is an increase in cultivation frequency around the
main market. Agricultural intensification is highly sensitive to accessibility by roads. The increase in land-use intensity
is also associated with low soil quality. These results suggest the need for policies to restore soil fertility for agricultural
sustainability. The models also provide a means for identifying functional relationships for in-depth analyses of land-use
change in Ghana. 相似文献
313.
D. L. Anderson P. C. Rosendahl 《Journal of the American Water Resources Association》1998,34(2):235-249
ABSTRACT: South Florida and the Everglades have been under intensive development since 1850 by Federal and State governments who encouraged and financed extensive drainage and hydraulic changes, primarily for agricultural settlement. Agricultural development of the sugar industry in the northern Everglades adjacent to Lake Okeechobee rapidly progressed only after the 1900s. Political and resource management conflicts have arisen because policies which once favored development are now being reversed by policies and regulation efforts to restore and conserve natural ecosystems. Currently, the environmental and ecological impacts of agricultural land use adjacent to natural wtlands of the Everglades are being assessed. The objectives of this paper are: (1) to outline the historical development of south Florida and the sugar industry, (2) to relate this history to political and management policy changes occurring as it pertains to ecosystem restoration and the multiuser competition for water/land resources, and (3) to propose how integrated resource management might be utilized for a sustainable Everglades and south Florida. This paper outlines the historical paradox of urban settlement, land development, and agricultural production, with efforts in the recent decade to acquire, manage, and preserve land and water resources for natural areas conservation. Only though the use of integrated resource management will the defined resource conflicts be mediated. 相似文献
314.
Crop derived biofuels such as (bio)ethanol are increasingly applied for automotive purposes. They have, however, a relatively low efficiency in converting solar energy into automotive power. The outcome of life cycle studies concerning ethanol as to fossil fuel inputs and greenhouse gas emissions associated with such inputs depend strongly on the assumptions made regarding e.g. allocation, inclusion of upstream processes and estimates of environmentally relevant in- and outputs. Peer reviewed studies suggest that CO2 emissions linked to life cycle fossil fuel input are typically about 2.1–3.0 kg CO2 kg−1 starch-derived ethanol. When biofuel production involves agricultural practices that are common in Europe there are net losses of carbon from soil and emissions of the greenhouse gas N2O. Dependent on choices regarding allocation, they may, for wheat (starch) be in the order of 0.6–2.5 kg CO2 equivalent kg−1 of ethanol. This makes ethanol derived from starch, or sugar crops, in Europe still less attractive for mitigating climate change. In case of wheat, changes in agricultural practice may reduce or reverse carbon loss from soils. When biofuel production from crops leads to expansion of cropland while reducing forested areas or grassland, added impetus will be given to climate change. 相似文献
315.
本文建立了新疆生产建设兵团农垦城镇类、等、级及基准地价的城镇土地等级体系,为兵团农垦城镇不同层次的土地管理提供了科学依据,对深化我国土地有偿使用制度改革,建立健全合理的土地市场,实现土地资源资产化等具有较好的理论和实践探索意义。 相似文献
316.
M. Hoffmann H. Johnsson A. Gustafson A. Grimvall 《Agriculture, ecosystems & environment》2000,80(3):1033
There is a need to examine long-term changes in nitrogen leaching from arable soils. The purpose of this study was to analyse variations in specific leaching rates (kg ha−1 per year) and gross load (Mg per year) of N from arable land to watercourses in Sweden from a historical perspective. The start of the study was set to 1865 because information on crop distribution, yield and livestock has been compiled yearly since then. The SOIL/SOILN model was used to calculate nitrogen leaching. Calculations were done for cereals, grass and bare fallow for three different soil types in nine agricultural regions covering a range of climatic conditions. Results indicate that both specific leaching rates and gross load of nitrogen in the middle of 19th century were approximately the same as they are today for the whole of south and central Sweden. Three main explanations for this were (1) large areas of bare fallow typical for the farming practice at the time; (2) enhanced mineralisation from newly cultivated land; and (3) low yield . From 1865, i.e. the start of the calculations, N leaching rates decreased and were at their lowest around 1930. During the same period, gross load was also at its lowest despite the fact that the acreage of arable land was at its most extensive. After 1930, average leaching increased by 60% and gross load by 30%, both reaching a peak in the mid-1970s to be followed by a declining trend. The greatest increase in leaching was in regions where the increase in animal density was largest and these regions were also those where the natural conditions for leaching such as mild winters and coarse-textured soils were found. Extensive draining projects occurred during the period of investigation, in particular an intensive exploitation of lakes and wetlands. This caused a substantial drop in nitrogen retention and the probable increase in net load to the sea might thus have been more affected by this decrease in retention than the actual increase in gross load. 相似文献
317.
调整农村能源结构是改善西部农业生态环境的核心问题之一 总被引:2,自引:0,他引:2
农村能源建设是农业生态系统的中心枢纽之一,通过小型高效沼气池发酵,一方面,改善了我国绝大部分地区农户用能结构及居住环境条件,促使农民的传统生活习惯向现代文明转变,提高农民的生活质量。另一方面,可减少薪柴的樵采,保护植树造林成果,提高森林覆盖率,治理水土流失,实现农作物秸杆的合理利用,增加土壤有机质,改善农业生态环境,促进农业可持续发展。 相似文献
318.
Peggy?Gunkel Estelle?Roth Bernard?FabreEmail author 《Environmental Chemistry Letters》2004,2(2):99-103
We studied copper uptake by maize grown on soils that have been contaminated with CuSO4. In soil the total copper level ranged from 24 to 135 mg kg–1. The copper distribution in soil fractions was assessed by sequential extraction, showing that anthropogenic copper is mainly concentrated in oxides fractions. The copper concentration of maize at the maturity stage reached values from 36.3 to 65.9 mg kg–1 compared to copper levels usually found in non-contaminated crops (5–30 mg kg–1). Here we demonstrate that copper can be accumulated by maize and that copper concentration in maize can be predicted by equations including copper concentration of soil fractions. 相似文献
319.
Reduced Diversity and Complexity in the Leaf-Litter Ant Assemblage of Colombian Coffee Plantations 总被引:3,自引:0,他引:3
Abstract: Coffee agroecosystems have recently undergone a dramatic intensification in Colombia, a megadiverse country, especially in terms of the nature of shade cover. We tested for changes in the composition, ecological associations, and diversity of ants (Hymenoptera: Formicidae) along a gradient of intensification of coffee production in the Colombian Andes. We surveyed 16 farms in two regions, classified into four management types: (1) forest (no agriculture), (2) organic polygeneric shaded coffee, (3) monogeneric shaded coffee, and (4) sun coffee (unshaded). Forty sampling units (20 1-m2 plots on the ground and 20 coffee bushes) were established at each farm between 2001 and 2002. We sampled with a mini-winkler litter extraction technique and through visual searching. Organic polygeneric shaded-coffee plantations contained significantly higher ant species richness, and their ant assemblages resembled the forest patches more than any other management type. The number of statistically significant associations among ant species dropped with production intensification, as did the number of ant species involved in such associations. The network of ant associations in shaded systems transformed into an extremely simplified network in sun coffee, with a few dominant ants extending almost entirely throughout the crop. Intensification of coffee agriculture not only caused loss of litter ant species (especially forest species) but also a reduction in the complexity of the ant assemblage in the leaf litter of this agroecosystem. 相似文献
320.
Susanna Reid Barry Smit Wayne Caldwell Suzanne Belliveau 《Mitigation and Adaptation Strategies for Global Change》2007,12(4):609-637
A vulnerability approach to climate change adaptation research is employed to explore prospects of agricultural adaptation
to climatic variability and change. The methodological approach focuses on the system of concern, in this case, farms in Perth
County, Ontario. Twenty-five interviews and four focus groups with farmers were used to identify climate risks on farms, and
to document farmers’ responses to conditions and risks associated with climate and weather. The information collected describes
a complex decision-making environment, with many forces both external and internal to the farm operation influencing management
decisions. Within this environment, climate and weather are consistently referred to as a significant force influencing both
farm operations and management decisions. Farmers have, however, developed a wide-range of anticipatory and reactive management
strategies to manage climate risks. While these have potential to address future climate-related risks and opportunities,
there are limits to adaptation, and an increase in the frequency of extreme events may exceed their adaptive capacities. Farmers
are also generally unaware and/or unconcerned about future climate change, which could constrain opportunities to adopt long-term
climate change adaptations. 相似文献