title: Exploring effective sampling design for monitoring soil organic carbon in degraded Tibetan grasslands.
abstract: The effects of climate change and human activities on grassland degradation and soil carbon stocks have become a focus of both research and policy. However, lack of research on appropriate sampling design prevents accurate assessment of soil carbon stocks and stock changes at community and regional scales. Here, we conducted an intensive survey with 1196 sampling sites over an area of 190 km(2) of degraded alpine meadow. Compared to lightly degraded meadow, soil organic carbon (SOC) stocks in moderately, heavily and extremely degraded meadow were reduced by 11.0%, 13.5% and 17.9%, respectively. Our field survey sampling design was overly intensive to estimate SOC status with a tolerable uncertainty of 10%. Power analysis showed that the optimal sampling density to achieve the desired accuracy would be 2, 3, 5 and 7 sites per 10 km(2) for lightly, moderately, heavily and extremely degraded meadows, respectively. If a subsequent paired sampling design with the optimum sample size were performed, assuming stock change rates predicted by experimental and modeling results, we estimate that about 5-10 years would be necessary to detect expected trends in SOC in the top 20 cm soil layer. Our results highlight the utility of conducting preliminary surveys to estimate the appropriate sampling density and avoid wasting resources due to over-sampling, and to estimate the sampling interval required to detect an expected sequestration rate. Future studies will be needed to evaluate spatial and temporal patterns of SOC variability.
authors.affiliation: State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, 26 Xinong Road, Yangling 712100, China.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Chang
authors.affiliation: University of the Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Bao
authors.affiliation: Key Laboratory of Alpine Ecology and Biodiversity of the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, 16 Lincui Road, Beijing 100101, China; CAS Center for Excellence in Tibetan Plateau Earth Science, Beijing 100101, China; Naqu Integrated Observation and Research Station on Ecology and Environment, Tibet University and Institute of Tibetan Plateau Research of the Chinese Academy of Sciences, Lasa 850012, China. Electronic address: wangsp@itpcas.ac.cn.
authors.forename: Shiping
authors.initials: S
authors.lastname: Wang
authors.affiliation: Key Laboratory of Adaptation and Evolution of Plateau Biota, Haibei Alpine Meadow Ecosystem Research Station, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, 23 Xinning Road, Xining 810008, China; University of the Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Xiaoxue
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Key Laboratory of Adaptation and Evolution of Plateau Biota, Haibei Alpine Meadow Ecosystem Research Station, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, 23 Xinning Road, Xining 810008, China.
authors.forename: Caiyun
authors.initials: C
authors.lastname: Luo
authors.affiliation: Key Laboratory of Adaptation and Evolution of Plateau Biota, Haibei Alpine Meadow Ecosystem Research Station, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, 23 Xinning Road, Xining 810008, China.
authors.forename: Zhenhua
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: World Agroforestry Centre (ICRAF) East and Central Asia Program, 12 Zhongguancun Nan Street, Beijing 100081, China.
authors.forename: Andreas
authors.initials: A
authors.lastname: Wilkes
mesh_terms: D001673:Biodegradation, Environmental; D018533:Biomass; D002244:Carbon / Q000032:analysis*; D057965:Carbon Sequestration; D004784:Environmental Monitoring / Q000379:methods*; D065948:Grassland; D010944:Plants; D018401:Sample Size; D012987:Soil / Q000737:chemistry*; D018609:Tibet
chemical_list: D012987:Soil; D002244:Carbon
keywords: Effective sample size; Grassland degradation; Sampling interval; Soil monitoring