| Western Ordos-East Alxa is located in the western part of Inner Mongolia,spanning desert steppe,grassland desertification,and typical desert belt.It is a region sensitive to vegetation change with arid climate and fragile ecological environment.In this study,five regions in the region:Alxazuo Banner,Dengkou County,Wuhai City,Hangjin Banner and Etuoke Banner were taken as the research objects.Based on the four periods of land use type data in 1990,2000,2010 and 2020,the GIMMS/NDVI3g in 1990–1999,the MOD13Q1/NDVI remote sensing data in2000–2020 and the meteorological data,the land use/vegetation cover change,the temporal and spatial change of NDVI and the relationship with climatic factors in the five regions were studied.The main conclusions are as follows:(1)The land use types in the study area are mainly unused land and grassland.During 1990–2020,the unused land area accounts for about65%of the total area of the study area,followed by grassland area,accounting for about 30%of the total area of the study area,and the area of cultivated land,forest land,water area and construction land is very small.(2)From 1990 to 2020,the land use types in the study area changed to varying degrees.From the perspective of quantitative change and percentage change,the area of cultivated land and construction land increased year by year.The area of cultivated land increased from1903.57 km~2(1.50%)to 2551.43 km~2(2.01%),and the area of construction land increased from 533.36 km~2(0.42%)to 1082.09 km~2(0.85%).The grassland area showed a downward trend,with an area of40534.98 km~2(31.87%)in 1990 and 36885.60 km~2(29.00%)in 2020.The overall area of woodland,water area and unused land changed little.(3)Subregionally,the main characteristics of each region are re flected in:Alxa Zuoqi unused land area accounted for more than80%,grassland area accounted for more than 10%,but the grasslan d area has a downward trend,from 17.07%in 1990 to 11.49%in2020.The unused land area accounted for the highest proportion in Dengkou County,but the area decreased year by year,from 70.06%in 1990 to 55.74%in 2020.Dengkou County is located in the Yellow River irrigation area.The available land is mainly cultivated land,and the cultivated land area increases from 15.31%to 27.78%year by year.The main land use types of Wuhai City,Hangjin Ba nner and Etuoke Banner are grassland,respectively,accounting for47.57%-56%,50.44%-52.47%,74.22%-78.39%;the second largest pr oportion of unused land in the three regions is 17.75%–19.53%,38.62%–41.29%,and 18.17%–22.57%,respectively.The difference is th at Wuhai City is an industrial city,and the proportion of constructi on land is also high,increasing from 11.12%in 1990 to 17.75%in2020,only second to unused land,and various types of land occu py a certain proportion.The change of forest land area in Hangjinqi also increased significantly from 0.29%in1990 to 1.32%in2020;the construction land area of Etuoke Banner has also changed signif icantly,from 0.34%in1990 to 0.93%in2020.(4)From the point of view of area transfer and transfer by region,the decrease of grassland area in Alxa Zuoqi was mainly converted to unused land.From 1990 to 2010,more than 98.00%of the area transferred from grassland to unused land,and 51.68%from 2010 to 2020transferred to unused land.The main sources of the increase in cultivated land area in Dengkou County are unused land and grassland.The transfer of unused land and grassland to cultivated land accounted for 97.00 per cent of the transfer of cultivated land in 1990-2000 and 2010-2020%,and 80.67%in 2000-2010;The increase of construction land in Wuhai City mainly comes from grassland,accounting for 40.81%,77.58%and 62.88%respectively in the three periods.The significant increase of forest land area in Hangjin Banner was mainly from 2010 to2020,mainly from unused land,accounting for 97.69%of forest land transfer area;The main source of construction land increase in Etuoke Banner is grassland,accounting for 93.58%,72.96%and 80.28%of the transferred area of construction land in the three periods respectively.(5)From the perspective of land use/land cover change dynamics in the study area,the highest overall dynamics in the five regions during1990-2020 was construction land,reaching 8.40%.From the regional point of view,from 1990 to 2020,the construction land has the highest dynamic degree in Alxa Left Banner,Wuhai City and Etuoke Banner,which are 25.63%,5.65%and 12.51%,respectively.The cultivated land has the highest dynamic degree in Dengkou County,which is 7.10%.The forest land has the highest dynamic degree in Hangjin Banner,which is27.55%.(6)The spatial distribution of NDVI in the growing season in the five regions of West Ordos-East Alxa increased gradually from west to east.On the time scale from 1990 to 2020,vegetation NDVI increased significantly(P<0.01),of which 16.52%increased significantly(P<0.05),and 6.64%reached extremely significant(P<0.01).The areas with significant NDVI were mainly distributed in the northeast of Alxa Zuoqi,Dengkou County and Hangjin Banner.From 2000 to 2020,98.05%showed an increasing trend,of which 81.87%showed a significant increase(P<0.05),and 67.58%reached a very significant increase(P<0.01).Parts of the significant increase were evenly distributed in the study area,and the overall growth of the study area was good.(7)The driving factors affecting the NDVI change were analyzed.On the time scale,NDVI and precipitation,NDVI and air temperature showed a very significant positive correlation between 1990 and 2020(P<0.01).The partial correlation coefficient of precipitation was 0.639,slightly higher than the value of 0.616 of air temperature.On the spatial scale,from 1990 to 1999,there was a significant positive correlation between NDVI and precipitation,accounting for 7.72%(P<0.05),which was mainly distributed in the northern part of Alxa Left Banner,Etuoke Banner and adjacent areas of Hangjin Banner.There was no significant correlation between NDVI and temperature.From 2000 to 2020,36.09%showed significant positive correlation between vegetation NDVI and precipitation(P<0.05),and 17.64%showed extremely significant positive correlation between vegetation NDVI and precipitation(P<0.01),which was mainly distributed in most parts of Etuoke Banner,the southern part of Hangjin Banner,the southernmost part of Azuo Banner and parts of the northern part.The significant positive correlation between NDVI and temperature accounted for 19%(P<0.05),and the extremely significant positive correlation area accounted for 3.46%(P<0.01),which was mainly distributed in the southwest of Alxa Left Banner.(8)The effects of water and heat in different periods of vegetation growth season on plant growth are different.The correlation between temperature,precipitation and NDVI in the early April to May and the late September to October of the growing season is not obvious.During the vigorous growth period from June to August,NDVI of vegetation had a very significant positive correlation with precipitation(P<0.01),and had a significant positive correlation with temperature(P<0.05). |
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