Shrubs proliferated within a six-year exclosure in a temperate grassland—Spatiotemporal relationships between vegetation and soil variables

查看全文 作　　者：Yong [1]Zhang;Qiong [1]Gao;Li [1]Xu;Mei [2]Yu;YuQiang [1]Tian

机构地区：[1]State Key Laboratory of Earth Surface Processes and Resources Ecology,College of Natural Resources and Technology,Beijing Normal University;[2]Department of Environmental Science,University of Puerto Rico-Rio Piedras

出　　处：《Research in Cold and Arid Regions》索引2014年第6卷第2期,共11页

基　　金：supported by the National Science Foundations of China with Grant No.41171445 摘　　要：Overgrazing has been considered one of the major causes that trigger shrub encroachment of grassland.Proliferation of shrubs in grassland is recognized as an important indicator of grassland degradation and desertification.In China,various conservation measures,including enclosures to reduce livestock grazing,have been taken to reverse the trend of grassland desertification,yet shrubs have been reported to increase in the grasslands over the past decades.In late 2007,we set up a 400-m-by-50-m exclosure in a long-term overgrazed temperate grassland in Inner Mongolia,with the objective to quantify the spatiotemporal relationship between vegetation dynamics,soil variables,and grazing exclusion.Soil moisture was continuously monitored within the exclosure,and cover and aboveground biomass of the shrubs were measured inside the exclosure in 2007,2009,2010,2012,and 2013,and outside the exclosure in 2012 and 2013.We found the average shrub cover and biomass significantly increased in the six years by 103% and 120%,respectively.The result supported the hypothesis that releasing grazing pressure following long-term overgrazing tends to trigger shrub invasion into grassland.Our results,limited to a single gradient,suggest that any conservation measures with quick release of overgrazing pressure by enclosure or other similar means might do just the opposite to accelerate shrub encroachment in grassland.The changes in vegetation cover and biomass were regressed on the temporal average of the soil moisture content by means of the generalized least square technique to quantify the effect of the spatial autocorrelation.The result indicates that the grass cover and biomass significantly increased with the top,but decreased with the bottom layer soil moisture.The shrub cover and biomass,on the other hand,decreased with the top,but increased with bottom soil moisture,although the regression coefficients for the shrubs were not statistically significant.Hence this study supports the two-layered soil model which assumes grasses and shrubs use belowground resources in different depths. 关键词：灌木植被温带草原土壤水分时空关系围封增殖生物量测定广义最小二乘法

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Shrubs proliferated within a six-year exclosure in a temperate grassland—Spatiotemporal relationships between vegetation and soil variables

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