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Effects of grassland management on the community structure, aboveground biomass and stability of a temperate steppe in Inner Mongolia, China 被引量:6
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作者 ZHANG Jinghui HUANG Yongmei +4 位作者 CHEN Huiying GONG Jirui QI Yu YANG Fei LI Engui 《Journal of Arid Land》 SCIE CSCD 2016年第3期422-433,共12页
Plant community structure responds strongly to anthropogenic disturbances, which greatly influence community stability. The changes in community structure, aboveground biomass(AGB), biodiversity and community stabil... Plant community structure responds strongly to anthropogenic disturbances, which greatly influence community stability. The changes in community structure, aboveground biomass(AGB), biodiversity and community stability associated with different management practices were studied with a three-year field investigation in a temperate steppe of Inner Mongolia, China. The species richness, Shannon-Wiener index, evenness, plant functional type abundance, AGB, temporal community stability, summed covariance, scaling coefficient and dominant species stability were compared among areas subjected to long-term reservation(R), long-term grazing(G), mowing since enclosure in 2008(M) and grazing enclosure since 2008(E). Site R had higher perennial grass abundance and lower species richness than sites G, M and E, although the AGB was not significantly different among the four sites. The species structure varied from a single dominant species at site R to multiple dominant species at sites G, M and E. The long-term reservation grassland had lower biodiversity but higher stability, whereas the enclosed grassland with/without mowing had higher biodiversity but lower stability. Different stability mechanisms, such as the compensatory dynamics, mean-variance scaling and dominant species stability were examined. Results showed that community stability was most closely related to the relative stability of the dominant species, which supports the biomass ratio hypothesis proposed by Grime. 展开更多
关键词 dominant species biodiversity indices mass ratio hypothesis variance-mean scaling compensatory dynamics
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Shear strength criteria for rock,rock joints,rockfill and rock masses:Problems and some solutions 被引量:43
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作者 Nick Barton 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2013年第4期249-261,共13页
Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has rece... Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has recently been better defined,and correct curvature or correct deviation from linear Mohr-Coulomb(MC) has finally been found.Standard shear testing procedures for rock joints,using multiple testing of the same sample,in case of insufficient samples,can be shown to exaggerate apparent cohesion.Even rough joints do not have any cohesion,but instead have very high friction angles at low stress,due to strong dilation.Rock masses,implying problems of large-scale interaction with engineering structures,may have both cohesive and frictional strength components.However,it is not correct to add these,following linear M-C or nonlinear Hoek-Brown(H-B) standard routines.Cohesion is broken at small strain,while friction is mobilized at larger strain and remains to the end of the shear deformation.The criterion 'c then σn tan φ' should replace 'c plus σn tan φ' for improved fit to reality.Transformation of principal stresses to a shear plane seems to ignore mobilized dilation,and caused great experimental difficulties until understood.There seems to be plenty of room for continued research,so that errors of judgement of the last 50 years can be corrected. 展开更多
关键词 Rock masses Critical state Rock joints Shear strength Non-linear friction Cohesion Dilation Scale effects Numerical modelling Stress transforms
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