Effect of Prosopis (mesquite) invasion and clearing on vegetation cover in semi-arid Nama Karoo rangeland,South Africa     

Thabisisani Ndhlovu  Suzanne J Milton  Karen J Esler 《African Journal of Range and Forage Science》2016,33(1):11-19

The Nama-Karoo is the largest of the three biomes that comprise the semi-arid Karoo-Namib ecoregion of southern Africa. Large tracts of Nama-Karoo rangeland have been invaded by alien leguminous trees of the genus Prosopis. We assessed the impact of Prosopis invasion and clearing on vegetation cover in heavily grazed Nama-Karoo rangeland on two sheep farms in the Beaufort West district of the Western Cape province of South Africa. Our results suggest that, below critical threshold cover levels, Prosopis trees do not affect indigenous vegetation and add to overall rangeland vegetation cover. However, once Prosopis cover exceeds critical thresholds, the trees begin to negatively impact on indigenous vegetation (especially grasses) and overall vegetation cover. In addition, our data suggest that vegetation cover recovers after Prosopis clearing, being temporarily higher than pre-invasion levels possibly as a result of enhanced post-invasion soil fertility. Lastly, our results suggest that Prosopis trees reduce rangeland erosion potential at low cover and increase it after they exceed critical threshold cover. Information about thresholds of Prosopis impact can be used to direct clearing efforts for maximum benefit when resources are limited.  相似文献   

Risk mitigation measures for pesticide runoff: How effective are they?     

Michael Klein  Judith Klein  Jens Flade  Dietlinde Großmann  Dominique Türkowsky  Isabel O'Connor  Simon Spycher  Stefan Reichenberger  Stephan Sittig  Sebastian Multsch  Kai Thomas 《Pest management science》2023,79(12):4897-4905

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生物多样性与地形及土壤因素对坡面产流产沙的耦合影响     

文博瑾  段高辉  温仲明 《草地学报》2023,31(4):1186-1197

生物多样性关系到生态系统的功能,而坡度和土壤因素是影响坡面产流产沙的重要因子。本研究基于黄土丘陵区生物多样性,并引入坡度、降雨前土壤含水量和土壤容重,探究其与坡面产流产沙总量的耦合关系。通过野外人工降雨试验,记录草本、灌木和乔木群落下的产流时间和产流产沙总量,并开展土壤植被调查。结果表明,与草本和乔木群落相比,灌木群落在延长产流开始时间和降低产沙总量上表现更优;植被群落功能离散度指数(FDiv)对产沙总量影响最大,Simpson指数(D)对产流总量影响最大,坡度仍然是不可忽视的第二重要影响因素;产流总量与坡度、土壤容重、D和功能丰富度指数(FRic)的回归关系优于产流总量分别与其的回归关系;产沙总量与坡度和FDiv指数的回归关系优于产沙总量分别与其的回归关系。植被保护与坡度改善将是该区水土保持规划工作的重点。  相似文献   

Energy-momentum Pseudo-tensor of Cylindrical Gravitational Waves of Both the Polarized States Based on Rosen-virbhadra Expression     

ZHANG Cui-juan  CHEN Wen-suo 《保鲜与加工》2006,(11):108-111

Using the expression of energy-momentum pseudo-tensor of cylindrical gravitational waves of both the polarized states, file authors got the expression of the energy and momentum after a great lot of calculations. The results are discussed, from these discussions, it is concluded that Cartesian coordinates is better than cylindrical coordinates to describe the cylindrical gravitational waves of both the polarized states.  相似文献   

A Receiving Surface of Perturbative Photon Fluxes in Interaction Between Gravitational Waves and EM Fields     

ZHANG Yi  WU Zhang-han 《保鲜与加工》2004,(9):60-63

According to Electrodynamics in curved spacetime, the interaction between gravitational waves (GW) and electromagnetic (EM) fields will produce perturbative electromagnetic fields. In a special EM system, namely, a Gaussian beam (Gb) propagating through a static magnetic field, the photon flux along the direction of the electric field of the Gb will be only a pure perturbative photon flux,when a GW propagates along the symmetric axis of a Gaussian beam. Detailed alanysis and calculation of the photon flux along several typical surfaces are performed, and a possible optimum plane which can receive perturbative photons up to 10~4s~(-1) is proposed. It is possible to provide an important method to detection of GW.  相似文献   

GIS在农业水土领域的应用与研究进展   总被引：5，自引：0，他引：5  

卢敏  张展羽 《中国农村水利水电》2004,(9):8-11

介绍了近年来国内外GIS在农业灌溉管理、精确农业和农业区划、土壤利用和土壤侵蚀方面的研究和应用情况，并对GIS在该领域的研究进行归纳和总结，此外探讨了GIS在当前农业领域应用的主要发展方向。  相似文献   

CFD技术在水轮机转轮抗空蚀改造中的应用   总被引：3，自引：1，他引：3  

宋海辉  匡和碧 《中国农村水利水电》2004,(10):100-102

CFD是用计算机来模拟流体的流场，建立流体机械最佳流道的流体动态分析软件，是当今先进的流体动力学模拟分析工具。介绍了CFD技术的理论基础，并且将其成功应用于锦江电站水轮机转轮的抗空蚀改造中，取得了良好的效果。  相似文献   

地表秸秆覆盖度图像识别技术的研究   总被引：1，自引：0，他引：1  

赵丽  张晋国 《农机化研究》2005,(4):240-242

农田地表秸秆覆盖是防止水土流失的一项主要措施,研究秸秆覆盖度与土壤风蚀、水蚀的定量关系对农田采取合理的覆盖形式有重要的指导意义。针对当前主要靠手工测试秸秆覆盖度存在效率低的问题,研究了如何应用MATLAB语言强大的图像处理功能来识别、分析秸秆图像。通过对样本图像类型的转换、灰度的均衡化和中值滤波等一系列的处理,得出较准确的秸秆覆盖面积和秸秆覆盖百分比,为准确快速测量秸秆覆盖度提供了测试手段。  相似文献   

湖北省大别丘陵区土壤侵蚀及其保护的研究     

杨补勤  王庆云 《华中农业大学学报》1989,8(4):364-368

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植被和梯田措施对坡沟系统细沟侵蚀调控作用     

董敬兵  时鹏  李占斌  李鹏  白璐璐  赵准  宋致华  赵倩卓  慕全鹏 《农业工程学报》2022,38(20):96-104

坡沟系统作为黄土丘陵沟壑区基本的地貌单元,也是黄土高原侵蚀泥沙的主要来源区。植被和梯田作为坡面水土流失治理的主要措施,对于土壤侵蚀控制和生态恢复发挥着重要的作用,定量评估林草、梯田对坡面细沟侵蚀的调控作用以及多措施协同配置问题对于黄土高原水土流失治理和生态保护具有重要意义。为了揭示植被和梯田的格局和配置对坡沟系统细沟侵蚀的协同调控作用,该研究采用人工模拟降雨,结合三维激光扫描技术,分析了坡面4种措施：上坡位植被（措施A）、下坡位植被（措施B）、梯田（措施C）、梯田+植被（措施D）对细沟侵蚀发生和演变过程的影响。结果表明：1）相同植被覆盖度下,下坡位的植被布设细沟最大长度较上坡位的植被布设细沟最大长度减小量更大;2）第1次降雨中,侵蚀率最大值达到3 500 g/min以上,第2次降雨过程中侵蚀率最大值仅为1 100 g/min以上,在各产流时间内第2次降雨侵蚀率均为第1次降雨侵蚀率的1/3～1/2;3）对于各措施下细沟沟长发育率由大到小表现为措施A(6.55 cm/min)、措施C(5.71 cm/min)、措施B(3.60 cm/min)、措施D(2.69 cm/min);4）梯田与植...  相似文献