| Global climate change,characterized mainly by global warming,is one of the biggest challenges to human society in the 21st century.Carbon emissions from fossil fuel combustion and land use/cover change(LUCC)are considered the primary driving forces causing global warming.LUCC has been recognized as one of the most important anthropogenic factors that influences the Earth surface.Present estimates indicate that about one third to one half of the Earth's land surface had been transformed in an unsustainable way by human activities.Such rapid change has directly influenced the ecosystem's structure,processes and functions,and consequently affecting the regional carbon cycle.Sited in arid and semi-arid climate zone,Inner Mongolia was sensitive to global climate change under intensive human activities.Inner Mongolia is characterized by a combination of rangeland-based livestock systems and mixed farming systems.Along with the population growth and economic development during the last half century,substantial LUCC has occurred over Inner Mongolia mainly due to over-grazing and over-cultivation.These changes caused ecological problems such as degradations of grassland and cropland,desertification and changes in carbon dynamics.In recent years,China's government established several ecological restoration projects(ERP)to mitigate the widespread ecological damage.Inner Mongolia was selected as a focus area of these programs for desertification control and grassland restoration.This makes the Province a good place for studying LUCC driven by vegetation restoration programs and its influence on regional carbon cycle.This study aimed to detect the ERP-induced LUCC in Inner Mongolia and its influence on regional carbon cycle.By combining the land use data and the CASA(Carnegie-Ames-Stanford Approach)model driving with multi-source NDVI and meteorological data,we analyzed the net primary productivity(NPP)dynamics in Inner Mongolia on different spatio-temporal scales,and assessed the effects of LUCC in the process.Meanwhile,we analyzed the ERP's role in the dynamics of coverage area,vegetation type transformations,vegetation coverage,landscape and NPP in Inner Mongolia grassland.The relative contributions of climate change and human activities in the process were differentiated quantitatively and spatially.This study accomplished the following tasks:1.The vegetation dynamics and its relationship with climate change on different spatial and temporal scales in Inner Mongolia during 2001-2010 were analyzed based on MODIS-NDVI data and climate data.The results showed that vegetation coverage increased from west to east across Inner Mongolia with a change rate of 0.2/10°N.During 2001-2010,the mean vegetation coverage was 0.57,0.4 and 0.16 in forest,grassland and desert biome,respectively,exhibiting evident spatial heterogeneities.There was a slight increase of vegetation coverage over the study period.Across Inner Mongolia,the area of which the vegetation coverage showed extremely significant and significant increase accounted for 11.25%and 29.13%of the area of whole region,respectively,while the area of which the vegetation coverage showed extremely significant and significant decrease accounted for 7.65%and 26.61%,respectively.The correlation analysis between vegetation coverage and climate showed that annual vegetation coverage was better correlated with precipitation,while the change of monthly vegetation coverage was consistent with both the change of temperature and precipitation,indicating that the vegetation growth within a year was more sensitive to the joint function of hydrothermal combination rather than either single climate factor.The vegetation coverage in forest biome was mainly driven by temperature on both inter-annual and inter-monthly scales,while that in desert biome was mainly influenced by precipitation on both the two temporal scales.In grassland biome,the yearly vegetation coverage had a better correlation with precipitation,while the monthly vegetation coverage could be influenced by both temperature and precipitation.In grassland biome,the impacts of precipitation on monthly vegetation coverage showed time-delay effects.2.Based on MODIS-NDVI data,land use data and meteorological data,spatio-temporal changes of the NPP of Inner Mongolia vegetation during 2001-2010 were simulated using CASA model.The relationships between NPP and climate factors were analyzed based on partial correlation coefficients of the two-group elements.The results showed that average annual NPP from 2001 to 2010 was 340.0 gCm-2yr-1,exhibiting obvious increase trend from southwest to northeast with a mean change rate of 200.5 gCm-2yr-1/10°.The mean NPP of forest,grassland,cropland and desert were 521.9?270.3?405.7 and 85.3 gCm-2yr-1,respectively,which showed significant differences.During 2001-2010,the average annual total NPP of Inner Mongolia vegetation was 322.7 TgCyr-1.ranging from 276.8 to 354.4 TgCyr-1.Over the 10 years period,extremely significant increase of vegetation NPP occurred in Alxa desert,the western margin of Mu Us sandy land,north of Hetao plain,the eastern and western margin of Hunshandak sandy land and northwest of Hulun Buir league,while extremely significant decrease of vegetation NPP mainly occurred in the grassland in the central of Inner Mongolia.Climate factors exerted various influences on different vegetation types.Temperature was the dominant driving force of NPP of forest,while precipitation influenced the NPP of grassland,cropland and desert vegetation more seriously.3.Based on MODIS-NDVI data,land use data and meteorological data,spatio-temporal changes of the NPP of Inner Mongolia grassland was simulated using CASA model.And the relationships between NPP and climate factors were analyzed based on partial correlation coefficients of the two-group elements.The results showed that average annual NPP from 2001 to 2010 was 281.3 gCm-2yr-1 in the study area,exhibiting obvious increase trend from southwest to northeast.The mean NPP in the unit area of meadow steppe is 431.8 gCm-2yr-1,in typical steppe is 288.7 gCm-2yr-1 and in desert steppe is 123.5 gCm-2yr-1.There was a rising trend in the grassland NPP of the ten years.Grassland NPP in Mu Us sandy land,Hunshandak sandy land,Horqing sandy,Hulun Buir league and southern slope of the Greater Hinggan Mountain exhibited the most obvious increase trend,while in Yin mountain region and the centre of Xilin gol league showed the most obvious decrease trend.As a whole,precipitation is the dominant driving force of NPP of Inner Mongolia grassland.NPP of meadow steppe correlated with both precipitation and temperature,with more dependence on temperature.Compared with temperature,precipitation influenced NPP of typical steppe and meadow steppe more seriously,particularly the later.4.We evaluate the effects of LUCC on regional NPP by combining the land use data for 2001 and 2009 and the CASA model driving with MODIS-NDVI and meteorological data.The results indicate that,between 2001 and 2009,the net change in the land cover types of Inner Mongolia occurred over about 15.02%of the surface area.Expansion of grassland areas and reduction of desert and cropland areas were the major forms of land conversion.According to the model results,mean NPP over the Provice increased from 290.5 to 322.8 gCm-2yr-1 between 2001 and 2009.The estimated total NPP for Inner Mongolia increased from 275,877.4 GgC in 2001 to 309,538.0 GgC in 2009.LUCC enhanced regional NPP directly,and the large-scale ERP could be the primary driving force for this increase.5.LUCC in the Inner Mongolia grassland and the consequent change in NPP were studied by combining the land use data of the study area for 2001 and 2009 derived from the MODIS global land cover product and the CASA model driven with MODIS-NDVI data.The results indicate that the area of Inner Mongolia grassland had a net increase of 77,993 km2 during the study period,which was mainly attributed to the conversion from desert and cropland.The total NPP of Inner Mongolia grassland increased by 29,432.71 GgCyr-1 during 2001-2009,of which the human activities and climate change were responsible for 80.23%and 19.77%,respectively.Land conversion and improved management increased grassland NPP directly,and the ecological restoration conducted by large-scale conservation programs could be the intrinsic driving force for this change.6.The area,NPP and landscape index(LSI)of Inner Mongolia grassland in 1985,1995,2000 and 2009 were analyzed.The grassland area in 1985,1995,2000 and 2009 were 0.54,0.57,0.53 and 0.61 million km2,respectively,which exhibited drastic temporal variation.The grassland of Inner Mongolia increased by 71,898 km2 in the past 24 years,accounting for 13.39%in 1985.The significant increase in the grassland biome during 2000-2009 was the dominant contributor responsible for this change.Compared with 1985-1995 and 1995-2000 periods,the landscape heterogeneity and fragmentation of Inner Mongolia grassland decreased during 2000 to 2009,and the dominance of grassland landscape increased in the process.During 1985-1995 and 1995-2000,the mean grassland NPP for the whole region decreased by 4.33%and 7.17%,respectively.But contrary to this trend,it increased largely during 2000-2009,about 36.55 gCm-2yr-1,15.55%of that in 2000,and reached the highest value in 2009 compared with the other three study years.The total grassland NPP for the whole region reached the highest value in 2009,increased by 32.91%of that in 2000 and 16.36%of that in 1985.7.The differences of LUCC and its impacts on NPP in Mongolia and Inner Mongolia during 2001 to 2009 were compared to detect the different roles of climate change and land use policies on a large spatial scale.Between 2001 and 2009,Mongolia grassland had a net increase of 88,798 km2.Conversion from desert to grassland was the major forms of land conversion(81,741 km2),which mainly occurred in the transitional zone of desert and grassland.The mean NPP of Mongolia increased by 4.5 gCm-2yr-1,and the total NPP incrased from 322,498.0 GgC in 2001 to 334,365.6 GgC in 2009,within which the total NPP of grassland increased by 31,719.8 GgC.During 2001 to 2009,the percentage increase of grassland area was higher in Inner Mongolia than in Mongolia.The percentage decrease of cropland area was higher in Mongolia than in Inner Mongolia,whereas the percentage decrease of desert area was higher in Inner Mongolia than in Mongolia.In Inner Mongolia,the mean NPP of all vegetation types showed an increase trend during 2001 to 2009.In Mongolia,the mean NPP of cropland,grassland,crop/natural vegetation and desert also showed an increase trend,while that of forest showed a decrease trend over the 9 years period.8.The net ecosystem productivity(NEP)dynamics of four grassland communities in Xilingol River Basin were analyzed by using BIOME-BGCmodel.During 1954 to 2012,the multi-year average NEP of Stipa baicalensis,Stipa grandis,Stipa krylovii and Leymus chinensis were 11.41,-7.82,-5.03,and 9.30 gCm-2 yr-1,respectively.The diurnal dynamic patterns of NEP could be expressed as inverse W curves,exhibiting releasing CO2-sequestrating CO2-releasing CO2 in a year.There was a close relationship between NEP and precipitations,and the correlations are on extremely significant level in Stipa grandis,Stipa krylovii and Leymus chinensis communities.NEP turned from negative to positive while annual precipitation of the four grassland communities was greater than 295.76 mm.There are several innovations as following:First,the LUCC and its impact on NPP in Inner Mongolia were analyzed on different spatio-temporal scales based on multi ecological indicators.For spatial scales,four individual years were selected in this study,including 1985,1995,2000 and 2009.For temporal scales,we divided Inner Mongolia into three biomes to compare the spatial difference,including the forest biome,the grassland biome and the desert biome,and Mongolia was also selected as a casa area to carry out spatial comparison.Furthermore,the ecological indicators selected in this study include coverage area,vegetation coverage,landscape metrics and NPP.Seconed,the relative contribution of the two factors were determined through comparing the change of potential NPP and actual NPP in the Inner Mongolia grassland.The potential NPP was used to estimate the climate induced NPP change,while the difference between potential NPP and actual NPP can reflect the human activities induced NPP change.Furthermore,the human activities here mainly include land conversion and the management alternatives,and the relative roles of the two factors were distinguished by comparing the difference between potential NPP and actual NPP in unchanged grassland and new developed grassland,separately.Third,the ecological effects of the ERP were assessed by analyzed the changes of coverage area,landscape index and NPP of grassland since the implementation of the GTGP and GWP.The disadvantages of the ERP were discussed in order to provide decision-making support for further adjustment of the ERP.LUCC in Inner Mongolia have been impacted by a range of factors,especially climate change and human activities.This study may provide decision-making support for rational grassland use and environmental protection.The results demonstrated that although grassland has expanded and desert has shrunk due to a steady humid period during 1985-1995,the warming and drying climate has led to consistent desertification since 1995,especially in arid regions.During 1985-2000,over grazing and large scale conversion from grassland to cropland contributed much to NPP decrease as well as a fragmented landscape.Since the implementation of the ERP in late 1990s and early 2000s,the regional grassland ecosystem has recovered to a certain extent,the area of desert and cropland decreased.The landscape heterogeneity and fragmentation of Inner Mongolia grassland decreased.However,these recoveries were mainly concentrated in ecological fragile regions.While large area of grassland was fenced off for restoration in the existing degraded grassland,rapid growth of livestock numbers seemed to pose a great threat to the grassland which was initially non-degraded or lightly degraded and neglected by the projects.Looking forward,the ERP,whose effectiveness has been evaluated to be positive at some local levels,should be further adjusted to balance environmental conservation and economic development.More plausible adaptation strategies to cope with both climate change and socioeconomic disturbances were needed for this purpose. |
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