青藏高原高寒草地总初级生产力变化的驱动机制及其对草地分类管理的启示（英文）
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摘要
气候变化和人类活动对植被生产力的相对贡献尚未有足够的认识。本研究基于过程模型模拟了2000–2015年气候因子主导的青藏高原高寒草地的总初级生产力(GPPp),并将MODIS的总初级生产力作为人类活动和气候变化共同作用下的总初级生产力(GPPa)。人类活动消耗的总初级生产力(GPPh)等于GPPp减去GPPa。约75.63%和24.37%面积的GPPa分别表现为增加和减少趋势。气候变化和人类活动分别主导了约42.90%和32.72%面积的GPPa的增加。相反,气候变化和人类活动分别主导了约16.88%和7.49%面积的GPPa的减少。草甸的GPPp和GPPh的变化趋势的绝对值分别大于草原的GPPp和GPPh的变化趋势的绝对值。所有海拔的GPPp的变化都大于GPPh的变化,当海拔≥5000m(草甸)、4600m(草原)或4800m(草甸+草原)时,GPPp和GPPh都表现为降低趋势,这表明气候变化主导着海拔5000 m(草甸)、4600 m(草原)、4800 m(草甸+草原)以下的GPPa,而人类活动的减少主导着海拔5000 m(草甸),4600 m(草原)、4800 m(草甸+草原)及其以上海拔的GPPa。因此,GPPa变化的原因随着海拔、区域和草地类型的变化而变化,草地应该采用分类管理。
The contribution of climatic change and anthropogenic activities to vegetation productivity are not fully understood. In this study, we determined potential climate-driven gross primary production(GPPp) using a process-based terrestrial ecosystem model, and actual gross primary production(GPPa) using MODIS Approach in alpine grasslands on the Tibetan Plateau from 2000 to 2015. The GPPa was influenced by both climatic change and anthropogenic activities. Gross primary production caused by anthropogenic activities(GPPh) was calculated as the difference between GPPp and GPPa. Approximately 75.63% and 24.37% of the area percentages of GPPa showed increasing and decreasing trends, respectively. Climatic change and anthropogenic activities were dominant factors responsible for approximately 42.90% and 32.72% of the increasing area percentage of GPPa, respectively. In contrast, climatic change and anthropogenic activities were responsible for approximately 16.88% and 7.49% of the decreasing area percentages of GPPa, respectively. The absolute values of the change trends of GPPp and GPPh of meadows were greater than those of steppes. The GPPp change values were greater than those of GPPh at all elevations, whereas both GPPp and GPPh showed decreasing trends when elevations were greater than or equal to 5000 m, 4600 m and 4800 m in meadows, steppes and all grasslands, respectively. Climatic change had stronger effects on the GPPa changes when elevations were lower than 5000 m, 4600 m and 4800 m in meadows, steppes and all grasslands, respectively. In contrast, anthropogenic activities had stronger effects on the GPPa changes when elevations were greater than or equal to 5000 m, 4600 m and 4800 m in meadows, steppes and all grasslands, respectively. Therefore, the causes of actual gross primary production changes varied with elevations, regions and grassland types, and grassland classification management should be considered on the Tibetan Plateau.
The contribution of climatic change and anthropogenic activities to vegetation productivity are not fully understood. In this study, we determined potential climate-driven gross primary production(GPPp) using a process-based terrestrial ecosystem model, and actual gross primary production(GPPa) using MODIS Approach in alpine grasslands on the Tibetan Plateau from 2000 to 2015. The GPPa was influenced by both climatic change and anthropogenic activities. Gross primary production caused by anthropogenic activities(GPPh) was calculated as the difference between GPPp and GPPa. Approximately 75.63% and 24.37% of the area percentages of GPPa showed increasing and decreasing trends, respectively. Climatic change and anthropogenic activities were dominant factors responsible for approximately 42.90% and 32.72% of the increasing area percentage of GPPa, respectively. In contrast, climatic change and anthropogenic activities were responsible for approximately 16.88% and 7.49% of the decreasing area percentages of GPPa, respectively. The absolute values of the change trends of GPPp and GPPh of meadows were greater than those of steppes. The GPPp change values were greater than those of GPPh at all elevations, whereas both GPPp and GPPh showed decreasing trends when elevations were greater than or equal to 5000 m, 4600 m and 4800 m in meadows, steppes and all grasslands, respectively. Climatic change had stronger effects on the GPPa changes when elevations were lower than 5000 m, 4600 m and 4800 m in meadows, steppes and all grasslands, respectively. In contrast, anthropogenic activities had stronger effects on the GPPa changes when elevations were greater than or equal to 5000 m, 4600 m and 4800 m in meadows, steppes and all grasslands, respectively. Therefore, the causes of actual gross primary production changes varied with elevations, regions and grassland types, and grassland classification management should be considered on the Tibetan Plateau.
引文
Chen B X,Zhang X Z,Tao J,et al.2014.The impact of climate change and anthropogenic activities on alpine grassland over the Qinghai-Tibet Plateau.Agricultural and Forest Meteorology,189:11-18.
Chu D,Pubu C R,Deji Y Z,et al.2013.Aboveground biomass estimate methods of grassland in the Central Tibet.Journal of Mountain Science,31(6):664-671.
Dorji T,Totland O,Moe S R,et al.2013.Plant functional traits mediate reproductive phenology and success in response to experimental warming and snow addition in Tibet.Global Change Biology,19(2):459-472.
Feng Y F,Wu J S,Zhang J,et al.2017a.Identifying the relative contributions of climate and grazing to both direction and magnitude of alpine grassland productivity dynamics from 1993 to 2011 on the Northern Tibetan Plateau.Remote Sensing,9(2).DOI:10.3390/rs9020136.
Feng Y F,Zhang X Z,Shi P L,et al.2017b.Livestock dynamic responses to climate change in alpine grasslands on the Northern Tibetan Plateau:forage consumption and time-lag effects.Journal of Resources and Ecology,8(1):88-96.
Field C B.2001.Global change-Sharing the garden.Science,294(5551):2490-2491.
Fu G,Shen Z X.2016.Environmental humidity regulates effects of experimental warming on vegetation index and biomass production in an alpine meadow of the Northern Tibet.PLoS One,11(10).DOI:10.1371/journal.pone.0165643.
Fu G,Shen Z X,Zhang X Z.2018.Increased precipitation has stronger effects on plant production of an alpine meadow than does experimental warming in the Northern Tibetan Plateau.Agricultural and Forest Meteorology,249:11-21.
Fu G,Shen Z X,Zhang X Z,et al.2012a.Calibration of MODIS-based gross primary production over an alpine meadow on the Tibetan Plateau.Canadian Journal of Remote Sensing,38(2):157-168.
Fu G,Shen Z X,Zhang X Z,et al.2012b.Response of microbial biomass to grazing in an alpine meadow along an elevation gradient on the Tibetan Plateau.European Journal of Soil Biology,52:27-29.
Fu G,Sun W,Li S W,et al.2017a.Modeling aboveground biomass using MODIS images and climatic data in grasslands on the Tibetan Plateau.Journal of Resources and Ecology,8(1):42-49.
Fu G,Zhang H,Li S,et al.2019.A meta-analysis of the effects of warming and elevated CO2 on soil microbes.Journal of Resources and Ecology,10(1):69-76.
Fu G,Zhang J,Shen Z X,et al.2017b.Validation of collection of 6MODIS/Terra and MODIS/Aqua gross primary production in an alpine meadow of the Northern Tibetan Plateau.International Journal of Remote Sensing,38(16):4517-4534.
Fu G,Zhang X Z,Yu C Q,et al.2014.Response of soil respiration to grazing in an alpine meadow at three elevations in Tibet.Scientific World Journal,DOI:10.1155/2014/265142.
Haberl H.1997.Human appropriation of net primary production as an environmental indicator:Implications for sustainable development.AMBIO,26(3):143-146.
Hinzman L D,Bettez N D,Bolton W R,et al.2005.Evidence and implications of recent climate change in northern Alaska and other arctic regions.Climatic Change,72(3):251-298.
Huang K,Zhang Y J,Zhu J T,et al.2016.The Influences of climate change and human activities on vegetation dynamics in the Qinghai-Tibet Plateau.Remote Sensing,8(10).DOI:10.3390/rs8100876.
Jahelnabi A E,Zhao J,Li C H,et al.2016.Assessment of the contribution of climate change and human activities to desertification in Northern Kordofan-Province,Sudan using net primary productivity as an indicator.Contemporary Problems of Ecology,9(6):674-683.
Klein J A,Harte J,Zhao X Q.2004.Experimental warming causes large and rapid species loss,dampened by simulated grazing,on the Tibetan Plateau.Ecology Letters,7(12):1170-1179.
Li Q,Zhang C L,Shen Y P,et al.2016.Quantitative assessment of the relative roles of climate change and human activities in desertification processes on the Qinghai-Tibet Plateau based on net primary productivity.Catena,147:789-796.
Liu J G,Diamond J.2005.China's environment in a globalizing world.Nature,435(7046):1179-1186.
Luo J,Xu D Y,Ren H Y.2013.The desertification dynamics in Ordos from2000 to 2010 and their relationship with climate change and human activities.Journal of Glaciology and Geocryology,35(1):48-56.
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Ni J.2002.Carbon storage in grasslands of China.Journal of Arid Environments,50(2):205-218.
Niu B,He Y,Zhang X,et al.2017.Satellite-Based inversion and field validation of autotrophic and heterotrophic respiration in an alpine meadow on the Tibetan Plateau.Remote Sensing,9(6):611.DOI:10.3390/rs9060611.
Niu S L,Wu M Y,Han Y,et al.2008.Water-mediated responses of ecosystem carbon fluxes to climatic change in a temperate steppe.New Phytologist,177(1):209-219.
Oberbauer S F,Tweedie C E,Welker J M,et al.2007.Tundra CO2 fluxes in response to experimental warming across latitudinal and moisture gradients.Ecological Monographs,77(2):221-238.
Piao S,Tan K,Nan H,et al.2012.Impacts of climate and CO2 changes on the vegetation growth and carbon balance of Qinghai-Tibetan grasslands over the past five decades.Global and Planetary Change,98-99:73-80.
Piao S L,Fang J Y,Zhou L M,et al.2006.Variations in satellite-derived phenology in China's temperate vegetation.Global Change Biology,12(4):672-685.
Raich J W,Rastetter E B,Melillo J M,et al.1991.Potential net primary productivity in South America:application of a global model.Ecological Applications,1(4):399-429.
Ravi S,Breshears D D,Huxman T E,et al.2010.Land degradation in drylands:Interactions among hydrologic-aeolian erosion and vegetation dynamics.Geomorphology,116(3-4):236-245.
Sharp E D,Sullivan P F,Steltzer H,et al.2013.Complex carbon cycle responses to multi-level warming and supplemental summer rain in the high Arctic.Global Change Biology,19(6):1780-1792.
Shen Z X,Fu G,Yu C Q,et al.2014.Relationship between the growing season maximum enhanced vegetation index and climatic factors on the Tibetan Plateau.Remote Sensing,6(8):6765-6789.
Shi Y,Wang Y,Ma Y,et al.2014.Field-based observations of regional-scale,temporal variation in net primary production in Tibetan alpine grasslands.Biogeosciences,11(7):2003-2016.
Tian H Q,Melillo J M,Kicklighter D W,et al.1998.Effect of interannual climate variability on carbon storage in Amazonian ecosystems.Nature,396(6712):664-667.
Turner D P,Ritts W D,Cohen W B,et al.2003.Scaling gross pimary production(GPP)over boreal and deciduous forest landscapes in support of MODIS GPP product validation.Remote Sensing of Environment,88(3):256-270.
Wang T,Sun J G,Han H,et al.2012.The relative role of climate change and human activities in the desertification process in Yulin region of northwest China.Environmental Monitoring and Assessment,184(12):7165-7173.
Wang Z,Luo T X,Li R C,et al.2013.Causes for the unimodal pattern of biomass and productivity in alpine grasslands along a large altitudinal gradient in semi-arid regions.Journal of Vegetation Science,24(1):189-201.
Wang Z Q,Zhang Y Z,Yang Y,et al.2016.Quantitative assess the driving forces on the grassland degradation in the Qinghai-Tibet Plateau,in China.Ecological Informatics,33:32-44.
Welker J M,Fahnestock J T,Henry G H R,et al.2004.CO2 exchange in three Canadian High Arctic ecosystems:response to long-term experimental warming.Global Change Biology,10(12):1981-1995.
Wessels K J,Prince S D,Malherbe J,et al.2007.Can human-induced land degradation be distinguished from the effects of rainfall variability?Acase study in South Africa.Journal of Arid Environments,68(2):271-297.
Wu J S,Zhang X Z,Shen Z X,et al.2013.Grazing-exclusion effects on aboveground biomass and water-use efficiency of alpine grasslands on the northern Tibetan Plateau.Rangeland Ecology&Management,66(4):454-461.
Wu J S,Zhang X Z,Shen Z X,et al.2014.Effects of livestock exclusion and climate change on aboveground biomass accumulation in alpine pastures across the Northern Tibetan Plateau.Chinese Science Bulletin,59(32):4332-4340.
Xu D Y,Kang X W,Zhuang D F,et al.2010.Multi-scale quantitative assessment of the relative roles of climate change and human activities in desertification-A case study of the Ordos Plateau,China.Journal of Arid Environments,74(4):498-507.
Xu D Y,Li C L,Zhuang D F,et al.2011.Assessment of the relative role of climate change and human activities in desertification:A review.Journal of Geographical Sciences,21(5):926-936.
Xu L L,Zhang X Z,Shi P L,et al.2007.Modeling the maximum apparent quantum use efficiency of alpine meadow ecosystem on Tibetan Plateau.Ecological Modelling,208(2-4):129-134.
Yan Y,Lu X Y.2015.Is grazing exclusion effective in restoring vegetation in degraded alpine grasslands in Tibet,China?Peer J,3(2015).DOI:10.7717/peerj.1020
Yang H F,Yao L,Wang Y B,et al.2017.Relative contribution of climate change and human activities to vegetation degradation and restoration in North Xinjiang,China.Rangeland Journal,39(3):289-302.
Yang X,Zhang K,Jia B,et al.2005.Desertification assessment in China:An overview.Journal of Arid Environments,63(2):517-531.
Yang Y,Wang Z Q,Li J L,et al.2016.Comparative assessment of grassland degradation dynamics in response to climate variation and human activities in China,Mongolia,Pakistan and Uzbekistan from 2000 to2013.Journal of Arid Environments,135:164-172.
Yang Y H,Fang J Y,Pan Y D,et al.2009.Aboveground biomass in Tibetan grasslands.Journal of Arid Environments,73(1):91-95.
Yang Y H,Piao S L 2006.Variations in grassland vegetation cover in relation to climatic factors on the Tibetan Plateau.Chinese Journal of Plant Ecology,30(1):1-8.
Yao T D,Xie Z C,Wu X L,et al.1991.Climate change since little ice age recorded by Dunde ice cap.Science in China Series B,34:760-767.
You Q,Kang S,Pepin N,et al.2010.Relationship between temperature trend magnitude,elevation and mean temperature in the Tibetan Plateau from homogenized surface stations and reanalysis data.Global and Planetary Change,71(1-2):124-133.
Yu C Q,Han F S,Fu G.2019.Effects of 7 years experimental warming on soil bacterial and fungal community structure in the Northern Tibet alpine meadow at three elevations.Science of the Total Environment,655:814-822.
Yu C Q,Zhang X Z,Zhang J,et al.2016.Grazing exclusion to recover degraded alpine pastures needs scientific assessments across the Northern Tibetan Plateau.Sustainability,8(11).DOI:10.3390/su8111162.
Zhang C X,Wang X M,Li J C,et al.2011.Roles of climate changes and human interventions in land degradation:a case study by net primary productivity analysis in China's Shiyanghe Basin.Environmental Earth Sciences,64(8):2183-2193.
Zhang T,Zhang Y J,Xu M J,et al.2015.Light-intensity grazing improves alpine meadow productivity and adaption to climate change on the Tibetan Plateau.Scientific Reports,5(2015).DOI:10.1038/srep15949.
Zhang X Z,Zhang Y G,Zhoub Y H.2000.Measuring and modelling photosynthetically active radiation in Tibet Plateau during April-October.Agricultural and Forest Meteorology,102(2-3):207-212.
Zhang Y,Dong S K,Gao Q Z,et al.2016.Climate change and human activities altered the diversity and composition of soil microbial community in alpine grasslands of the Qinghai-Tibetan Plateau.Science of the Total Environment,562:353-363.
Zhao M S,Heinsch F A,Nemani R R,et al.2005.Improvements of the MODIS terrestrial gross and net primary production global data set.Remote Sensing of Environment,95(2):164-176.
Zhou W,Gang C C,Zhou F C,et al.2015.Quantitative assessment of the individual contribution of climate and human factors to desertification in northwest China using net primary productivity as an indicator.Ecological Indicators,48:560-569.
Zhou W,Sun Z G,Li J L,et al.2013.Desertification dynamic and the relative roles of climate change and human activities in desertification in the Heihe River Basin based on NPP.Journal of Arid Land,5(4):465-479.
Zhuang Q,He J,Lu Y,et al.2010.Carbon dynamics of terrestrial ecosystems on the Tibetan Plateau during the 20th century:an analysis with a process-based biogeochemical model.Global Ecology and Biogeography,19(5):649-662.
Chu D,Pubu C R,Deji Y Z,et al.2013.Aboveground biomass estimate methods of grassland in the Central Tibet.Journal of Mountain Science,31(6):664-671.
Dorji T,Totland O,Moe S R,et al.2013.Plant functional traits mediate reproductive phenology and success in response to experimental warming and snow addition in Tibet.Global Change Biology,19(2):459-472.
Feng Y F,Wu J S,Zhang J,et al.2017a.Identifying the relative contributions of climate and grazing to both direction and magnitude of alpine grassland productivity dynamics from 1993 to 2011 on the Northern Tibetan Plateau.Remote Sensing,9(2).DOI:10.3390/rs9020136.
Feng Y F,Zhang X Z,Shi P L,et al.2017b.Livestock dynamic responses to climate change in alpine grasslands on the Northern Tibetan Plateau:forage consumption and time-lag effects.Journal of Resources and Ecology,8(1):88-96.
Field C B.2001.Global change-Sharing the garden.Science,294(5551):2490-2491.
Fu G,Shen Z X.2016.Environmental humidity regulates effects of experimental warming on vegetation index and biomass production in an alpine meadow of the Northern Tibet.PLoS One,11(10).DOI:10.1371/journal.pone.0165643.
Fu G,Shen Z X,Zhang X Z.2018.Increased precipitation has stronger effects on plant production of an alpine meadow than does experimental warming in the Northern Tibetan Plateau.Agricultural and Forest Meteorology,249:11-21.
Fu G,Shen Z X,Zhang X Z,et al.2012a.Calibration of MODIS-based gross primary production over an alpine meadow on the Tibetan Plateau.Canadian Journal of Remote Sensing,38(2):157-168.
Fu G,Shen Z X,Zhang X Z,et al.2012b.Response of microbial biomass to grazing in an alpine meadow along an elevation gradient on the Tibetan Plateau.European Journal of Soil Biology,52:27-29.
Fu G,Sun W,Li S W,et al.2017a.Modeling aboveground biomass using MODIS images and climatic data in grasslands on the Tibetan Plateau.Journal of Resources and Ecology,8(1):42-49.
Fu G,Zhang H,Li S,et al.2019.A meta-analysis of the effects of warming and elevated CO2 on soil microbes.Journal of Resources and Ecology,10(1):69-76.
Fu G,Zhang J,Shen Z X,et al.2017b.Validation of collection of 6MODIS/Terra and MODIS/Aqua gross primary production in an alpine meadow of the Northern Tibetan Plateau.International Journal of Remote Sensing,38(16):4517-4534.
Fu G,Zhang X Z,Yu C Q,et al.2014.Response of soil respiration to grazing in an alpine meadow at three elevations in Tibet.Scientific World Journal,DOI:10.1155/2014/265142.
Haberl H.1997.Human appropriation of net primary production as an environmental indicator:Implications for sustainable development.AMBIO,26(3):143-146.
Hinzman L D,Bettez N D,Bolton W R,et al.2005.Evidence and implications of recent climate change in northern Alaska and other arctic regions.Climatic Change,72(3):251-298.
Huang K,Zhang Y J,Zhu J T,et al.2016.The Influences of climate change and human activities on vegetation dynamics in the Qinghai-Tibet Plateau.Remote Sensing,8(10).DOI:10.3390/rs8100876.
Jahelnabi A E,Zhao J,Li C H,et al.2016.Assessment of the contribution of climate change and human activities to desertification in Northern Kordofan-Province,Sudan using net primary productivity as an indicator.Contemporary Problems of Ecology,9(6):674-683.
Klein J A,Harte J,Zhao X Q.2004.Experimental warming causes large and rapid species loss,dampened by simulated grazing,on the Tibetan Plateau.Ecology Letters,7(12):1170-1179.
Li Q,Zhang C L,Shen Y P,et al.2016.Quantitative assessment of the relative roles of climate change and human activities in desertification processes on the Qinghai-Tibet Plateau based on net primary productivity.Catena,147:789-796.
Liu J G,Diamond J.2005.China's environment in a globalizing world.Nature,435(7046):1179-1186.
Luo J,Xu D Y,Ren H Y.2013.The desertification dynamics in Ordos from2000 to 2010 and their relationship with climate change and human activities.Journal of Glaciology and Geocryology,35(1):48-56.
Melillo J M,McGuire A D,Kicklighter D W,et al.1993.Global climate change and terrestrial net primary production.Nature,363(6426):234-240.
Ni J.2002.Carbon storage in grasslands of China.Journal of Arid Environments,50(2):205-218.
Niu B,He Y,Zhang X,et al.2017.Satellite-Based inversion and field validation of autotrophic and heterotrophic respiration in an alpine meadow on the Tibetan Plateau.Remote Sensing,9(6):611.DOI:10.3390/rs9060611.
Niu S L,Wu M Y,Han Y,et al.2008.Water-mediated responses of ecosystem carbon fluxes to climatic change in a temperate steppe.New Phytologist,177(1):209-219.
Oberbauer S F,Tweedie C E,Welker J M,et al.2007.Tundra CO2 fluxes in response to experimental warming across latitudinal and moisture gradients.Ecological Monographs,77(2):221-238.
Piao S,Tan K,Nan H,et al.2012.Impacts of climate and CO2 changes on the vegetation growth and carbon balance of Qinghai-Tibetan grasslands over the past five decades.Global and Planetary Change,98-99:73-80.
Piao S L,Fang J Y,Zhou L M,et al.2006.Variations in satellite-derived phenology in China's temperate vegetation.Global Change Biology,12(4):672-685.
Raich J W,Rastetter E B,Melillo J M,et al.1991.Potential net primary productivity in South America:application of a global model.Ecological Applications,1(4):399-429.
Ravi S,Breshears D D,Huxman T E,et al.2010.Land degradation in drylands:Interactions among hydrologic-aeolian erosion and vegetation dynamics.Geomorphology,116(3-4):236-245.
Sharp E D,Sullivan P F,Steltzer H,et al.2013.Complex carbon cycle responses to multi-level warming and supplemental summer rain in the high Arctic.Global Change Biology,19(6):1780-1792.
Shen Z X,Fu G,Yu C Q,et al.2014.Relationship between the growing season maximum enhanced vegetation index and climatic factors on the Tibetan Plateau.Remote Sensing,6(8):6765-6789.
Shi Y,Wang Y,Ma Y,et al.2014.Field-based observations of regional-scale,temporal variation in net primary production in Tibetan alpine grasslands.Biogeosciences,11(7):2003-2016.
Tian H Q,Melillo J M,Kicklighter D W,et al.1998.Effect of interannual climate variability on carbon storage in Amazonian ecosystems.Nature,396(6712):664-667.
Turner D P,Ritts W D,Cohen W B,et al.2003.Scaling gross pimary production(GPP)over boreal and deciduous forest landscapes in support of MODIS GPP product validation.Remote Sensing of Environment,88(3):256-270.
Wang T,Sun J G,Han H,et al.2012.The relative role of climate change and human activities in the desertification process in Yulin region of northwest China.Environmental Monitoring and Assessment,184(12):7165-7173.
Wang Z,Luo T X,Li R C,et al.2013.Causes for the unimodal pattern of biomass and productivity in alpine grasslands along a large altitudinal gradient in semi-arid regions.Journal of Vegetation Science,24(1):189-201.
Wang Z Q,Zhang Y Z,Yang Y,et al.2016.Quantitative assess the driving forces on the grassland degradation in the Qinghai-Tibet Plateau,in China.Ecological Informatics,33:32-44.
Welker J M,Fahnestock J T,Henry G H R,et al.2004.CO2 exchange in three Canadian High Arctic ecosystems:response to long-term experimental warming.Global Change Biology,10(12):1981-1995.
Wessels K J,Prince S D,Malherbe J,et al.2007.Can human-induced land degradation be distinguished from the effects of rainfall variability?Acase study in South Africa.Journal of Arid Environments,68(2):271-297.
Wu J S,Zhang X Z,Shen Z X,et al.2013.Grazing-exclusion effects on aboveground biomass and water-use efficiency of alpine grasslands on the northern Tibetan Plateau.Rangeland Ecology&Management,66(4):454-461.
Wu J S,Zhang X Z,Shen Z X,et al.2014.Effects of livestock exclusion and climate change on aboveground biomass accumulation in alpine pastures across the Northern Tibetan Plateau.Chinese Science Bulletin,59(32):4332-4340.
Xu D Y,Kang X W,Zhuang D F,et al.2010.Multi-scale quantitative assessment of the relative roles of climate change and human activities in desertification-A case study of the Ordos Plateau,China.Journal of Arid Environments,74(4):498-507.
Xu D Y,Li C L,Zhuang D F,et al.2011.Assessment of the relative role of climate change and human activities in desertification:A review.Journal of Geographical Sciences,21(5):926-936.
Xu L L,Zhang X Z,Shi P L,et al.2007.Modeling the maximum apparent quantum use efficiency of alpine meadow ecosystem on Tibetan Plateau.Ecological Modelling,208(2-4):129-134.
Yan Y,Lu X Y.2015.Is grazing exclusion effective in restoring vegetation in degraded alpine grasslands in Tibet,China?Peer J,3(2015).DOI:10.7717/peerj.1020
Yang H F,Yao L,Wang Y B,et al.2017.Relative contribution of climate change and human activities to vegetation degradation and restoration in North Xinjiang,China.Rangeland Journal,39(3):289-302.
Yang X,Zhang K,Jia B,et al.2005.Desertification assessment in China:An overview.Journal of Arid Environments,63(2):517-531.
Yang Y,Wang Z Q,Li J L,et al.2016.Comparative assessment of grassland degradation dynamics in response to climate variation and human activities in China,Mongolia,Pakistan and Uzbekistan from 2000 to2013.Journal of Arid Environments,135:164-172.
Yang Y H,Fang J Y,Pan Y D,et al.2009.Aboveground biomass in Tibetan grasslands.Journal of Arid Environments,73(1):91-95.
Yang Y H,Piao S L 2006.Variations in grassland vegetation cover in relation to climatic factors on the Tibetan Plateau.Chinese Journal of Plant Ecology,30(1):1-8.
Yao T D,Xie Z C,Wu X L,et al.1991.Climate change since little ice age recorded by Dunde ice cap.Science in China Series B,34:760-767.
You Q,Kang S,Pepin N,et al.2010.Relationship between temperature trend magnitude,elevation and mean temperature in the Tibetan Plateau from homogenized surface stations and reanalysis data.Global and Planetary Change,71(1-2):124-133.
Yu C Q,Han F S,Fu G.2019.Effects of 7 years experimental warming on soil bacterial and fungal community structure in the Northern Tibet alpine meadow at three elevations.Science of the Total Environment,655:814-822.
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