| The Ulan Buh Desert is one of the sources of sandstorms in northwest China.Due to environmental changes and improper human interference,the ecological balance of the desert is destroyed and the desertification trend is presented.The distribution and change of desert vegetation are important indicators of desertification.Artemisia desertorum 、Haloxylon ammodendron 、 Nitraria tangutorum are dominant species of ulan buh desert,constitutes the important ecological protective barriers,under the background of global climate change,its distribution pattern changes gradually cause the attention of researchers,deeply understanding of species distribution area of desertification area and its response to climate change,analysis of desert vegetation restoration potential,which will contribute to the protection and restoration of desert vegetation.This study in use of the machine learning method,combined with field investigation,species identification based on multi-source remote sensing data,using the method of point pattern analysis and species distribution model,to analysis the spatial and temporal variations of ulan buh desert with different species distribution pattern,find out the ulan change of different dominant species in ulan buh desert vegetation pattern and the main natural driving factors,Analysis of species distribution in response to the change of different environmental factors and speculated the distribution pattern of dominant species change in ulan buh desert and the suitable distribution of desert vegetation,analysis the inner natural driving force of changes of dominant species and its environmental response,during the Holocene intermediate and predict its future under the background of global warming,desert vegetation restoration potential analysis,and the specific conclusions are as follows:(1)Multi-source remote sensing species identificationIn this study based on mid-resolution Landsat 8 images,high-resolution GF-2 data,using the maximum likelihood method,neural network and support vector machine(SVM),supervised classification method and so on,to identify the mainly desert species of the study area,precision analysis through the confusion matrix,the result shows that maximum likelihood identification precision is the highest.Based on high-resolution visible light and lidar data,compared with the traditional maximum likelihood method,the random forest method combined with VDVI index and texture features is a better method to identify desert plants,and the species identification accuracy can reach 84.17%.(2)Point pattern characteristicsFrom 2006 to 2019,both Artemisia desertorum and Haloxylon ammodendron shrub showed an aggregation distribution pattern,in which Artemisia desertorum shrub expanded from 0-16 m to 0-25 m,and Haloxylon ammodendron shrub decreased from 0-18 m to 0-10 m,showing a trend of random distribution on a larger scale.Intraspecific correlation of Artemisia desertorum shrub gradually weakened,while the intraspecific relationship of Haloxylon ammodendron shrub gradually strengthened.Habitat heterogeneity is an important factor.According to the point pattern of Nitraria tangutorum shrub,from 2006 to 2019,the random distribution of Nitraria tangutorum shrub at each scale gradually showed an aggregation distribution within 0-20 m scale.Habitat heterogeneity began to play a role in the spatial distribution pattern of Nitraria tangutorum shrub,which showed a smaller aggregation distribution and an enhanced intra-specific relationship.Among the three dominant species,only Haloxylon ammodendron and Artemisia desertorum showed specific spatial relationships at different scales.With the passage of time,the interspecific interaction scale of Haloxylon ammodendron and Artemisia desertorum decreased,and the competition relationship intensified.Habitat heterogeneity had no significant effect on the interspecific relationship of Haloxylon ammodendron and Artemisia desertorum in typical plots.(3)Suitable areas for species distribution and migration trends in different climate scenariosSeven species distribution models(Domain,Bioclim,GLM,RF,Maxent,SVM,and Malhalobis)were used to simulate the distribution of three dominant shrub species in the study area.The model accuracy of different species was different,but the maximum entropy model was the best model for the three species.Based on the maximum entropy model,the currently suitable habitat area of three dominant shrub species was predicted.The high suitable distribution area of Artemisia desertorum shrub is mainly concentrated in the northeast of the study area,the middle suitable area is the buffer zone of the high suitable area,the low suitable area is in the middle of the study area,and the unsuitable area is mainly in the west of the study area.The high suitability area of Haloxylon ammodendron shrub is mainly concentrated in the middle and south of the study area,the middle suitability area is the buffer zone of the high suitability area,the low suitability area is basically distributed in the whole study area,and the unsuitability area is mainly in the south and east of the study area.The high suitability area of Nitraria tangutorum is mainly distributed in the north and central south of the study area,along the Jilantai Lake.With the increase of CO2 emission intensity over time,the migration direction of Artemisia desertorum shrub changed from southwest to north,and that of Haloxylon ammodendron shrub changed from northwest to east,while the main migration direction of Nitraria tangutorum shrub was southwest,and the migration distance was gradually shortened.From the perspective of historical evolution,by analyzing the changes in the suitable distribution areas of species during the middle Holocene scenario,it can be concluded that the changes in the suitable distribution areas of desertification species caused by climate change in the next 30 years are equivalent to the changes in the historical 6000 years.Therefore,it is necessary to pay enough attention to the future increase of CO2 emissions and adopt appropriate strategies to slow down the driving force of climate change on desertification,so as to achieve a longer period of harmonious coexistence between mankind and nature.(4)Driving force of main environmental variablesThe main environmental variables for the growth and distribution of Artemisia desertorum is annual average temperature,the suitable range of annual average temperature was 7.4℃-9℃,and the threshold was 8.4℃.The main environmental variables for the growth and distribution of Haloxylon ammodendron were terrain factors and rainfall factors.The suitable range of elevation is 1014m-1070 m with a threshold of 1062 m,and the suitable range of rainfall is 90-105 mm with a threshold of 95 mm.The main environmental variable of Nitraria tangutorum growth and distribution is groundwater depth,the suitable range is 0.6-2.5m,and the optimal adaptive threshold is 1.68 m.(5)Driving forces of desertificationThe results of the quantitative study of desertification driving forces based on random forest algorithm show that from 2006 to 2018,the desertification reversal areas of Ulan Buh Desert are mainly distributed in the hinterland of ulan Buh Desert and along the Yellow River,and gradually change from severe and very severe desertification to mild and more mild desertification.(6)Vegetation restoration potentialLeaf area index of vegetation is the important index of plant communities,ecological potential and relief valve value,spatial distribution of ulan buh desert presents the northeast high,southwest low overall space distribution characteristics,and the overall security threshold value is less than the ecological potential.The desert ecosystem is more fragile,potential vegetation restoration is still present an unstable state.There is still 45% room for improvement of vegetation restoration potential in the study area.The potential for improvement along the Yellow River is large,while the potential for restoration in the central and southern regions is moderate. |
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