| Under the background of global warming,the vegetation growth in Inner Mongolia has undergone significant changes,which has put great pressure on the local sustainable livelihood.The detection and attribution of changes in vegetation growth is fundamental to our understanding of the scientific basis of changes in vegetation ecological environment and is necessary for decision-makers to manage and develop the ecological environment sustainably.The vegetation index is an approximate simulation of vegetation growth.At present,remotely sensed vegetation datasets have been widely used in the study of vegetation dynamics at regional or global scales.It should be noted that different datasets have different abilities to simulate vegetation growth,and there is still a lack of reliable comparison between multiple datasets.In addition,the vegetation growth may shift over time,that is,the change of vegetation greening and browning trend may be masked by a stable linear trend over a long time scale.Therefore,in this study,the large and small integrals of NDVI(Normalized Difference Vegetation Index)and LAI(Leaf Area Index)during the growing season obtained from GIMMS(Global Inventory Modelling and Mapping Studies)NDVI3g and GIMMS LAI3 g datasets were used as effective indicators to characterize the vegetation growth in Inner Mongolia and the consistency of multiple indicators was evaluated.Then,Inner Mongolia was divided into three main ecoregions(forest,grassland,desert),and the dynamic changes in vegetation growth were monitored to capture their turning point of trend shifts.Previous studies on the conclusion that "vegetation growth in Inner Mongolia is affected by climate" were still in the qualitative stage,and the specific contribution of each factor could not be quantitatively described.This study took the most widely distributed grassland in Inner Mongolia as the research object,exploring the contribution of each climate factor(temperature,precipitation,solar radiation,soil moisture,and drought index)to the changes in grassland vegetation growth in Inner Mongolia based on two quantitative methods of relative contribution.In addition,considering the time lag of vegetation response to climate change,this study further quantified the time-lag effect of grassland vegetation response to climate factors on a monthly scale.Based on the above analysis,the main conclusions of this study are as follows:(1)In general,the four indicators(large/small integrals of NDVI and LAI)were consistent in representing the temporal and spatial changes in vegetation growth in Inner Mongolia and could be used as indicators to measure the changes in vegetation growth in Inner Mongolia.Based on linear regression,the four indicators showed a significant increase trend(p < 0.05;t-test)from 1982 to 2016.Specifically,these indicators showed an increasing trend(greening)in most areas of Inner Mongolia,while only a few areas showed a decreasing trend(browning),which indicated that the greening trend was dominant in Inner Mongolia vegetation.Considering the hypothesis of "possible nonlinear shifts in vegetation growth trend",this study found that the greening process of vegetation in Inner Mongolia was still prevalent.Although this process was more manifested as a setback in the process of vegetation greening or a shift from a browning trend to a greening trend.The proportion of the area where the trend shifts occurred has increased significantly since 1999,indicating that the vegetation growth in Inner Mongolia in the last ten years was more susceptible to external disturbances.(2)The results of the two quantitative methods of relative contribution consistently showed that soil moisture was the main factor that dominated the changes in grassland vegetation growth in Inner Mongolia from 1982 to 2016,dominating more than 60% of the changes in grassland vegetation growth in Inner Mongolia.Secondly,temperature,precipitation,and solar radiation dominated about 10% of the grassland vegetation growth in Inner Mongolia,mainly in central and western parts of Inner Mongolia.In the early period(1982-1996),water conditions(precipitation and soil moisture)dominated the changes in vegetation growth in most areas of Inner Mongolia.The areas dominated by precipitation were mainly distributed in central Inner Mongolia,while the areas dominated by soil moisture were mainly distributed in eastern and western Inner Mongolia.In the latest period(2002-2016),soil moisture became the dominant factor affecting vegetation growth in most grassland areas in Inner Mongolia.In particular,the grassland area dominated by precipitation gradually changed to dominated by soil moisture,and the positive effect of soil moisture on the changes in grassland vegetation growth in Inner Mongolia increased significantly over time(p < 0.05;t-test),which indicated that the enhanced soil moisture control on Inner Mongolia’s grassland vegetation growth.(3)A conspicuous time-lag effect between grassland vegetation growth and climate factors was detected in Inner Mongolia.Among them,the relationship between temperature and grassland vegetation growth was a contemporaneous response,that is,the temperature of the current month affected the grassland vegetation growth of the current month,while the effect of other variables lags behind.In the central and eastern Inner Mongolia,the precipitation of the current month affected the vegetation growth of grassland in the next month,while the western region showed a response relationship in the same period,that is,the precipitation of the current month affected the vegetation growth of grassland in the current month.The lag effect of solar radiation on the growth of grassland vegetation was mainly manifested as the solar radiation of the current month affected the vegetation growth of grassland in the next month.The soil moisture of the current month also mainly affected the growth of grassland vegetation in the next month.The effect of short-term drought on grassland vegetation growth also showed that the short-term drought conditions of the current month affected grassland vegetation growth in the next month.This study revealed the greening,browning trends,and nonlinear shifts of vegetation growth in Inner Mongolia with the help of a variety of vegetation growth indicators,and quantified the specific contribution of climatic factors to grassland vegetation growth in Inner Mongolia,and put forward the detailed information and dominating factors of changes in vegetation growth in Inner Mongolia.This is of great scientific and practical significance to understand the vegetation ecosystem in Inner Mongolia and further explore the grassland management model adapted to climate change and maintain the stable development of the animal husbandry economy. |
PDF Full Text Request