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991.
Soil erosion continues to represent a major environmental issue in China. This paper considers some of the practical difficulties of assessing the severity of soil erosion in subtropical southern China, with particular reference to a case study in Fujian Province. The administration of soil and water conservation and procedures for erosion evaluation in an area of southern China are outlined. Although the hierarchy of bodies involved in soil conversation is impressive compared to other countries in subtropical environments, little is known about the dynamics of erosion, its impact on productivity or its contribution to sediment yields. 相似文献
992.
云南金沙江干热河谷区因高温干旱、水资源匮乏、水土流失严重、生态环境退化、社会经济条件差及不合理开发等因素,抑制了区内光热资源潜力的发挥及自然资源的综合开发与经营。根据流域的环境特点、自然资源特征及利用现状,因地制宜地提出流域自然资源综合开发与经营模式。 相似文献
993.
该文介绍了甘肃长江流域11个利用类型的木本植物107科319属1364种,阐述了分布特点及其开发利用途径,提出了合理适度的开发意见。 相似文献
994.
The riparian forests along braided rivers are dynamic, frequently rejuvenated by floods and channel changes, and thus dominated
by pioneer to middle stages of succession; they are sites of high biodiversity in some regions. The Lower Eygues River (drainage
area 1150 km2 in southeastern France) is such a braided river system with large alluvial forests dominated by Salix alba, Populus alba, and P. nigra. It was identified as a site of ecological interest by the EU under the Natura 2000 program. Such forests elsewhere in Europe have been identified as reference ecosystems. We documented the historical evolution
of this alluvial forest from detailed (1:2500 scale) early 19th C parcel maps, early 20th C topographic maps, aerial photography
from 1947 to 1996, and field surveys of topography and riparian vegetation in 1997–1998. Our results show that in 1830, the
channel was wide, aggraded, and agricultural pressure extended literally to the channel edge. With decline in the rural population
and reduced agricultural and grazing pressure in the catchment, erosion rates declined. Reduced sediment supply led to channel
narrowing and incision. This channel narrowing, coupled with reduced agricultural pressure along the banks, has allowed riparian
forest to colonize former active channel areas, especially within late 19th-century 20th century flood dykes. In recent decades,
aggregate mining, and clearing for recreation and agriculture have fragmented the forest. Thus, the alluvial forest of the
Lower Eygues is largely an artifact of changing human land-use over the past century, a context that should frame efforts
for preservation and restoration. 相似文献
995.
996.
997.
B.S. Corrêa-Ferreira L.A. Domit L. Morales R.C. Guimarães 《Integrated Pest Management Reviews》2000,5(2):75-80
A Soybean IPM system was deployed in large, continuous river basin areas. The system was designed to improve the productivity of the rural environment by restoring balance among pests and their natural enemies. The system was developed with the active participation of various governmental, industrial and academic institutions, and it was based on the main approaches utilized by the EMBRAPA soybean IPM program referred here as IPM-Soybean.The work of IPM-Soybean in microbasins is being implemented in five counties in Paraná state (Campo Mourão, Mamborê, Missal, Cambé and Toledo) in an area of approximately 18,020ha of soybean involving 343 producers at various stages of implementation. The results obtained in the Rio do Campo basin in Campo Mourão, after four years of IPM-Soybean, showed drastic changes in pest control practices. Mean number of insecticide applications per cropping year in the river basin fell from 2.8 (1993/94 season) to 1.23 four seasons later. Biological control of the velvetbean caterpillar, Anticarsia gemmatalis, by Baculovirus anticarsia increased 57%, from 205ha treated with this biological product in the 1993/94 season to 2730ha in 1998. A mean of about 300,000 Trissolcus basalis (Wollaston) adults were released per year to control soybean stink bugs. As a consequence of the parasitoid release and the use of more selective insecticides, the number of insecticide applications to control stink bugs was significantly reduced. After two soybean seasons with IPM-Soybean in the river basin, mean applications for stink bugs decreased from 0.81 before the program started to 0.09 in 1996. The mean number of applications in the region and the state respectively were 9.20 and 11.44 times greater. In 1997 and 1998, the results again showed very low population densities of stink bugs in the river basin area, with a consequent reduction in insecticide applications for the control of these pests. Furthermore there was a substantial improvement in the range of products used in this area for soybean pest control. Broad spectrum products, used in 97.5% of the applications before start of IPM-Soybean (1993/94), were replaced with more selective products, especially biologicals and growth regulators. The latter had rarely been used by the river basin producers before the study (0.6% of the applications), but they accounted for 35.8% of the applications after four seasons with IPM-Soybean. IPM-Soybean developed in river basins has resulted in a more stable control system that, in turn, provides greater long-term equilibrium between the pests and the natural enemies populations in these soybean producing areas. 相似文献
998.
Muhammad Altaf Arain William James Shuttleworth Blake Farnsworth John Adams Omer Lutfi Sen 《Agricultural and Forest Meteorology》2000,100(4)
Micrometeorological variables measured in the BIOSPHERE-2 Center (B2C) enclosed rain forest biome for 1 year were compared with similar measurements made in the Amazon rain forest. In the B2C rain forest, the overlying glass and supporting structure significantly reduces (by approximately a factor of two) the incoming solar radiation. Monthly mean values of above-canopy and within-canopy air temperature, vapor pressure, and vapor pressure deficit are reasonably similar to those of the Amazon rain forest, but there are marked differences in the above-canopy values of these variables in the Arizona summer. Monthly mean diurnal trends also show significant differences. Measurements of vertical air temperature gradient clearly showed two very distinct environments in the 27.4 m high rain forest dome during daylight hours. There is a comparatively cool and fairly well-mixed environment (which is reasonably similar to that found in a natural rain forest) below about 10 m and a hot, thermally stable environment above about 15 m. The nature of the atmospheric turbulence within the B2C rain forest also is significantly different from that normally found in natural rain forests. There is little turbulent mixing above the forest canopy in this enclosed environment. These findings are important for guiding the operation and use of this experimental rain forest facility in future research and for understanding how the rain forest biome functions in an enclosed environment. 相似文献
999.
中国绿洲地域系统研究 总被引:24,自引:6,他引:18
本文论述了中国干旱区山地的自然特征及其在向荒漠平原盆地提供细粒土状物质 ,输送地表水及浅层地下水 ,建构荒漠背景下的特殊生境 ,从而导致局地绿洲化等方面的重要作用 ,并对绿洲系统、盆地地域系统、山地—盆地地域系统进行初步探讨。认为正是绿洲系统对荒漠盆地平原地域系统和山地—盆地地域系统的从属性 ,决定了绿洲面积的有限性和保护山地—盆地地域系统的必要性。 相似文献
1000.