Shennongjia represents an area of considerable plant biodiversity,not only for China but for the whole world.The numerous species are distributed along an altitude gradient.The genus Fagus,commonly known as Beeches,co...Shennongjia represents an area of considerable plant biodiversity,not only for China but for the whole world.The numerous species are distributed along an altitude gradient.The genus Fagus,commonly known as Beeches,constitutes one of the dominant woody species of the humid temperate forests in China.This paper deals with the community structure of a mixed,broadleaved deciduous-evergreen beech forest dominated by the Fagus engleriana and Cyclobalanopsis oxyodon,which occurs along an altitude gradient range in this area.The community consists of 46 woody species,belonging to 22 families and 27 genera.The tree layer can be divided into three sub-strata.The upper layer is composed of deciduous trees,80.7%of which is F.engleriana.The second and third layers are dominated by the evergreen species,such as C.oxyodon and the Rhododendron hypoglaucum.These species increase from 55.9%in the second layer to 80.5%in the third,and regeneration at that rate allows us to assume that the stability of the community may be guaranteed.The micro-site heterogeneity plays an important role in maintaining species diversity in plant communities.In this research,a terrain surface of 0.96hm 2 was simulated using the digital elevation model(DEM)in order to analyze the influence of the topography on plant community structures on a small scale.The slope relief aspect obtained with the DEM showed an accentuated heterogeneity.Semivariance analysis was used to measure the heterogeneity scale.The range and nugget variance of the semivariograms for slope were 285.8 and 280.5,respectively;for aspect,were 21.8 and 498,respectively.The elevated value of the nugget variance suggested that even on a small scale,the topographic variations influenced the species distribution.Twenty-four species were selected to estimate the correlation coefficient between the slope,aspect,and orientation.Then based on the correlation results using the Square Euclidean Distance cluster analysis,the 24 species were divided into four groups.展开更多
Root tensile strength is an important factor controlling the performance of bio-slope stabilization works. Due to evapotranspiration and climate factors, the root moisture content and its suction can vary seasonally i...Root tensile strength is an important factor controlling the performance of bio-slope stabilization works. Due to evapotranspiration and climate factors, the root moisture content and its suction can vary seasonally in practice and may not equal soil suction. The influences of suction and root moisture contents were investigated on Chrysopogon zizanioides(vetiver grass) root tensile strength. The root specimens were equilibrated with moist air in different suction conditions(0, 10, 20, and 50 kPa), prior to root tension tests. The root-water characteristic curve or relationship between root moisture and suction, was determined. The increase in suction resulted in decreased tensile strengths of the grass roots, particularly those with diameter of about 0.2 mm, which constituted 50.7% of all roots. For 1 mm roots, the tensile strength appeared to be unaffected by suction increase. The average root tensile strengths were used to estimate the root cohesion in slope stability analysis to find variation of safety factors of a bioengineered slope in different suction conditions. The analysis showed that the critical condition of slope with the lowest factor of safety would happen when the soil suction was zero and the root suction was high. Such condition may occur during a heavy rain period after a prolonged drought.展开更多
文摘Shennongjia represents an area of considerable plant biodiversity,not only for China but for the whole world.The numerous species are distributed along an altitude gradient.The genus Fagus,commonly known as Beeches,constitutes one of the dominant woody species of the humid temperate forests in China.This paper deals with the community structure of a mixed,broadleaved deciduous-evergreen beech forest dominated by the Fagus engleriana and Cyclobalanopsis oxyodon,which occurs along an altitude gradient range in this area.The community consists of 46 woody species,belonging to 22 families and 27 genera.The tree layer can be divided into three sub-strata.The upper layer is composed of deciduous trees,80.7%of which is F.engleriana.The second and third layers are dominated by the evergreen species,such as C.oxyodon and the Rhododendron hypoglaucum.These species increase from 55.9%in the second layer to 80.5%in the third,and regeneration at that rate allows us to assume that the stability of the community may be guaranteed.The micro-site heterogeneity plays an important role in maintaining species diversity in plant communities.In this research,a terrain surface of 0.96hm 2 was simulated using the digital elevation model(DEM)in order to analyze the influence of the topography on plant community structures on a small scale.The slope relief aspect obtained with the DEM showed an accentuated heterogeneity.Semivariance analysis was used to measure the heterogeneity scale.The range and nugget variance of the semivariograms for slope were 285.8 and 280.5,respectively;for aspect,were 21.8 and 498,respectively.The elevated value of the nugget variance suggested that even on a small scale,the topographic variations influenced the species distribution.Twenty-four species were selected to estimate the correlation coefficient between the slope,aspect,and orientation.Then based on the correlation results using the Square Euclidean Distance cluster analysis,the 24 species were divided into four groups.
基金the financial supports from the Chaipattana FoundationKasetsart University Research and Development Institute(KURDI)the scholarship for his PhD studies provided by the Faculty of Engineering,Kasetsart University
文摘Root tensile strength is an important factor controlling the performance of bio-slope stabilization works. Due to evapotranspiration and climate factors, the root moisture content and its suction can vary seasonally in practice and may not equal soil suction. The influences of suction and root moisture contents were investigated on Chrysopogon zizanioides(vetiver grass) root tensile strength. The root specimens were equilibrated with moist air in different suction conditions(0, 10, 20, and 50 kPa), prior to root tension tests. The root-water characteristic curve or relationship between root moisture and suction, was determined. The increase in suction resulted in decreased tensile strengths of the grass roots, particularly those with diameter of about 0.2 mm, which constituted 50.7% of all roots. For 1 mm roots, the tensile strength appeared to be unaffected by suction increase. The average root tensile strengths were used to estimate the root cohesion in slope stability analysis to find variation of safety factors of a bioengineered slope in different suction conditions. The analysis showed that the critical condition of slope with the lowest factor of safety would happen when the soil suction was zero and the root suction was high. Such condition may occur during a heavy rain period after a prolonged drought.
