排序方式: 共有2条查询结果,搜索用时 156 毫秒
1
1.
Ranjeet John Jiquan Chen Youngwook Kim Zu-tao Ou-yang Jingfeng Xiao Hoguen Park Changliang Shao Yaoqi Zhang Amartuvshin Amarjargal Ochirbat Batkhshig Jiaguo Qi 《Landscape Ecology》2016,31(3):547-566
Context
The Mongolian Plateau, comprising Inner Mongolia, China (IM) and Mongolia (MG) is undergoing consistent warming and accelerated land cover/land use change. Extensive modifications of water-limited regions can alter ecosystem function and processes; hence, it is important to differentiate the impacts of human activities and precipitation dynamics on vegetation productivity.Objectives
This study distinguished between human-induced and precipitation-driven changes in vegetation cover on the plateau across biome, vegetation type and administrative divisions.Methods
Non-parametric trend tests were applied to the time series of vegetation indices (VI) derived from MODIS and AVHRR and precipitation from TRMM and MERRA reanalysis data. VI residuals adjusted for rainfall were obtained from the regression between growing season maximum VI and monthly accumulated rainfall (June–August) and were used to detect human-induced trends in vegetation productivity during 1981–2010. The total livestock and population density trends were identified and then used to explain the VI residual trends.Results
The slope of precipitation-adjusted EVI and EVI2 residuals were negatively correlated to total livestock density (R2 = 0.59 and 0.16, p < 0.05) in MG and positively correlated with total population density (R2 = 0.31, p < 0.05) in IM. The slope of precipitation-adjusted EVI and EVI2 residuals were also negatively correlated with goat density (R2 = 0.59 and 0.19, p < 0.05) and sheep density in MG (R2 = 0.59 and 0.13, p < 0.05) but not in IM.Conclusions
Some administrative subdivisions in IM and MG showed decreasing trends in VI residuals. These trends could be attributed to increasing livestock or population density and changes in livestock herd composition. Other subdivisions showed increasing trends residuals, suggesting that the vegetation cover increase could be attributed to conservation efforts.2.
Muneto Hirobe Junji Kondo Altangerel Enkhbaatar Narantsetseg Amartuvshin Noboru Fujita Keiji Sakamoto Ken Yoshikawa Knut Kielland 《Journal of Soils and Sediments》2013,13(7):1123-1132
Purpose
Small-scale soil heterogeneity relates to productivity and biodiversity and is crucial to understand. Soil heterogeneity could be affected by vegetation structure, and large mammal grazers could modify it through herbivory and excretion. The objective is to clarify the effects of livestock grazing on the small-scale (~3 m) soil heterogeneity in three types of Mongolian grasslands.Materials and methods
We sampled soils from inside (ungrazed) and outside (grazed) exclosures in three vegetation types: forest-steppe, shrub-steppe, and desert-steppe. We measured laboratory rates of soil net nitrogen (N) mineralization and net nitrification and geostatistically analyzed heterogeneity.Results and discussion
Average rates of net N mineralization and net nitrification were lower at shrub-steppe and desert-steppe and were decreased by grazing. Semivariograms showed vegetation-induced heterogeneity in ungrazed plots, except for net nitrification at forest-steppe. We found linear change with distance under dense and uniform vegetation at forest-steppe, 1.3 m patch under patchy vegetation at shrub-steppe, and linear change, but with much smaller semivariance, under sparse and poor vegetation at desert-steppe. At forest-steppe, grazing randomized the spatial patterns of net N mineralization and net nitrification. At shrub-steppe and desert-steppe, grazing greatly decreased the semivariances of net N mineralization and net nitrification as well as their averages, and the soil heterogeneity was virtually disappeared.Conclusions
Grazing in Mongolian grasslands homogenized the spatial patterns of net N mineralization and net nitrification, irrespective of their original spatial patterns determined by the differences in vegetation structure. 相似文献
1