| Karst environment is a kind of fragile ecological environment with slow soil formation process,shallow and discontinuous,small water holding capacity,not suitable for vegetation growth and the ecological system is easy to reverse under the action of an external conditions.Southwest was less developed areas,and was also a region of fragile ecological environment.In the frail geo-ecological environmental background,once the surface overlying vegetation destruction,soil and water loss soon and underlying bedrock directly exposed to the surface,the rocky desertification spread quickly.In recent years,in order to prevent desertification and control water and soil losses and protect the ecological environment,the government implemented a series of ecological vegetation restoration projects in southwest.Dynamic monitoring and evaluation vegetation coverage was an important part for monitoring and evaluation of water and soil loss and ecological environment.It was the fundamental data of karst area ecological construction project evaluation.The ground survey which was the traditional measurement method was time-consuming and with great limitations,difficult to promote.The development of remote sensing technology made it possible for large scale macroscopic monitoring of vegetation coverage.It was a great significance for the karst area of ecological environment construction.Chongqing was the junction of the Yangtze River economic belt and an important ecological barrier.The karst area was widely distributed and ecological environment was fragile.The Three Gorges Reservoir Region had great ecological risk,serious contradiction between poverty alleviation and environmental protection.For this reason,the dynamic change and spatial distribution pattern of vegetation coverage and rocky desertification in Chongqing were studied based on the MODIS datasets using the method of dimidiate pixel modeling and anomaly percentage and trend analysis and variance coefficient and distribution indexes and landscape index and residual analysis during 20002015.The results showed that:?1?The vegetation coverage was dominated by medium coverage in annual,summer and autumn,while it was dominated by low coverage in spring and winter.The proportion of the little coverage and low coverage were highest in winter,mainly in hechuan,jiangjin and yongchuan;The proportion of the medium coverage was highest in summer,mainly in liangping,nanchuan and dianjiang;The proportion of the high coverage was highest in autumn,mainly in chengkou,wuxi and wulong.Little coverage was much more than normal in the springs of 2000,2002 and 2003,and in the autumns of 2001 and 2006,and in the winter of 2011,mainly in dianjiang,bishan,dazu and tongliang.Low coverage was much more than normal in the autumns of 2000 and 2001,mainly in wuxi,fengjie and zhongxian.High coverage was much less than normal in the autumns of 2000 and 2008 and in the spring of 2014,mainly in yongchuan,jiangjin and hechuan.The change trend of vegetation coverage was dominated by unchanged type?81.12%?,followed by increased type?15.04%?and decreased type?3.84%?.The proportion of decreased type was highest in winter,mainly in rongchang,tongnan and wushan.The proportion of unchanged type was the highest in autumn,mainly in chengkou,wuxi and pengshui.The proportion of increased type was the highest in spring,mainly in qijiang,tongnan and rongchang.The fluctuation of vegetation coverage was dominated by slight fluctuation?63.60%?,followed by stable?21.72%?,moderate fluctuation?11.68%?and serious fluctuation?3.00%?.The proportion of stable was highest in summer,mainly in the chengkou,qijiang and jiangjin;The proportion of slight fluctuation was highest in autumn,mainly in liangping,qijiang and nanchuan;The proportion of moderate fluctuation and serious fluctuation was highest in winter,mainly in rongchang,dazu,tongliang,yongchuan and chongqing*.?2?The fragmentation and diversity of vegetation coverage were lower in summer,while the connectivity and aggregation were higher.Compared with the non-karst area,the fragmentation and diversity of vegetation coverage were higher,while the connectivity and aggregation were lower.The fragmentation and aggregation of little coverage were lower;The fragmentation of low coverage was lower and the aggregation was higher;The fragmentation of medium coverage was higher and the aggregation was lower;The fragmentation and aggregation of high coverage were higher.The fragmentation and diversity of the change trend of vegetation coverage were lower in autumn,while the connectivity and aggregation were higher.Compared with the non-karst area,the fragmentation and connectivity of the change trend of vegetation coverage were higher,while the diversity and aggregation were lower;The fragmentation and aggregation of decreased type were lower,while the fragmentation of increased type was higher and the aggregation was lower.The fragmentation and diversity of the fluctuation of vegetation coverage were lower in autumn,while the connectivity and aggregation were higher.Compared with the non-karst area,the fragmentation and connectivity of the fluctuation of vegetation coverage were higher,while the diversity and aggregation were lower;the fragmentation of stable and serious fluctuation were higher and the aggregation were lower,while the fragmentation and aggregation of slight fluctuation and moderate fluctuation were higher.?3?In terrain distribution,the little coverage and low coverage were mainly distributed in the area where the elevation was below 600m and slope was below 15°and aspect was northern,western.The medium coverage and high coverage mainly distributed in the area where the elevation was above 600m and slope was above 15°and aspect was eastern,southern.In the seasonal change,from spring to summer,the little coverage increased in the area where the elevation was below 300m and slope was215°and aspect was eastern,southern;The low coverage increased in the area where the elevation was below 300m and slope was above 6°and aspect was northern,western;The medium coverage increased in the area where the elevation was below 800m and slope was below 6°and aspect was northern,western;The high coverage increased in the area where the elevation was above 1400m and slope was below 15°and aspect was eastern,southern.From autumn to winter,the little coverage increased in the area where the elevation was above 300m and slope was above 15°and aspect was northern;The low coverage increased in the area where the elevation was above 500m and slope was above 6°and aspect was northern,eastern;The medium coverage increased in the area where the elevation was above 800m and slope was above 6°and aspect was eastern,southern;The high coverage increased in the area where the elevation was below 1100m and slope was above 15°and aspect was western.The decreased type was mainly distributed in the area where the elevation was below 400m and slope was below 6°and aspect was northern,western.The increased type was mainly distributed in the area where the elevation was 4001200m and slope was above 6°and aspect was eastern,southern.In the seasonal change,from spring to summer,the decreased type increased in the area where the elevation was 200600m and slope was below 6°and aspect was eastern,western;The increased type increased in the area where the elevation was above 900m and slope was above 6°and aspect was eastern,southern.From autumn to winter,the decreased type increased in the area where the elevation was 300500m and above 1300m and slope was below 2°and above 15°and aspect was southern;The increased type increased in the area where the elevation was 5001300m and slope was above 6°and aspect was northern,eastern and western.The stable was mainly distributed in the area where the elevation was below400800m and slope was above 15°and aspect was eastern,southern.The slight fluctuation was mainly distributed in the area where the elevation was above 1300m and slope was above 6°and aspect was northern.The moderate fluctuation was mainly distributed in the area where the elevation was 8001300m and slope was 615°and aspect was western.The serious fluctuation was mainly distributed in the area where the elevation was below 400m and slope was below 6°and aspect was flat.In the seasonal change,from spring to summer,the slight fluctuation increased in the area where the elevation was below 400m and above 1200m and slope was below 6°and aspect was northern,western;The moderate fluctuation increased in the area where the elevation was below 200m and 6001400m and slope was above 6°and aspect was western;The serious fluctuation increased in the area where the elevation was below 400m and slope was below 6°and aspect was southern,western.From autumn to winter,the slight fluctuation increased in the area where the elevation was above 500m and slope was above 6°and aspect was eastern,southern;The moderate fluctuation increased in the area where the elevation was 4001100m and slope was 625°and aspect was eastern,southern;The serious fluctuation increased in the area where the elevation was above400m and slope was above 6°and aspect was northern,western.?4?A regression model of vegetation coverage was established based on precipitation and temperature,and the contribution rate of climate and human activities to vegetation coverage was analyzed by residual error analysis.From 2000 to 2013,the area mainly affected by human activities accounted for 25.88%and the area mainly affected by climate accounted for 74.12%.The reverse effect of human activity was mainly in the area where the country was jiangjin,yongchuan and bishan,and the elevation was below 400m and slope was below 6°and aspect was western;The positive effect was mainly in the area where the country was wuxi,chengkou and shizhu,and the elevation was above 1100m and slope was above 25°and aspect was northern,southern.The climatic inhibition was mainly in the area where the country was qianjiang,youyang and pengshui,and the elevation was 7001100m and slope was625°;The climatic facilitation was mainly in the area where the country was tongnan,dazu and liangping,and the elevation was 400700m and aspect was flat,eastern.The proportion of vegetation positively correlated with precipitation accounted for47.26%,and the correlation was the highest in changshou,while positively correlated with temperature accounted for 39.33%,and the correlation was the highest in wuxi.In the seasonal change,in spring,the proportion of vegetation positively correlated with precipitation accounted for 51.05%,and the correlation was the highest in yunyang,while positively correlated with temperature accounted for 44.08%,and the correlation was the highest in wushan;In summer,the proportion of vegetation positively correlated with precipitation accounted for 49.70%,and the correlation was the highest in wanzhou,while positively correlated with temperature accounted for 61.22%,and the correlation was the highest in yunyang;In autumn,the proportion of vegetation positively correlated with precipitation accounted for 37.43%,and the correlation was the highest in kaixian,while positively correlated with temperature accounted for20.98%,and the correlation was the highest in xiushan;In winter,the proportion of vegetation positively correlated with precipitation accounted for 46.53%,and the correlation was the highest in dianjiang,while positively correlated with temperature accounted for 61.72%,and the correlation was the highest in jiangjin.The decreased type was mainly distributed in farmland,waters and construction land,while the increased type was mainly distributed in woodland and grassland.In the distribution of vegetation decreased,farmland and construction land were mainly in summer,woodland and grassland in winter,and waters in spring.In the distribution of vegetation increased,farmland,waters and construction land were mainly in autumn,and woodland and grassland in summer.The stable was mainly distributed in farmland,and the slight fluctuation in woodland and grassland,and the moderate fluctuation and serious fluctuation in waters and construction land.In the distribution of stable,farmland and woodland were mainly in summer,and grassland in autumn,and waters in spring,and construction land in winter.In the distribution of slight fluctuation,farmland was mainly in autumn,and woodland and grassland in winter,and waters and construction land in summer.In the distribution of moderate fluctuation,farmland was mainly in autumn,and woodland and grassland in spring,and waters and construction land in summer.In the distribution of serious fluctuation,farmland and woodland were mainly in winter,and grassland in spring,and waters and construction land in summer.?5?Based on the vegetation coverage,the quantitative monitoring model of rocky desertification was established by the data of rock exposure rate,slope and land use to analyze the evolution characteristics of rocky desertification.From 2001 to 2015,the area and degree of rocky desertification gradually decreased.Karst rocky desertification was dominated by moderate rocky desertification?57.33%?,followed by slight rocky desertification?31.95%?,severe rocky desertification?9.61%?,and intense severe rocky desertification?1.11%?.The proportion of slight rocky desertification showed an increase trend,and moderate rocky desertification increased first then decreased,and severe and extremely severe rocky desertification showed a decrease trend.The type of rocky desertification evolution was dominated by the step way?49.47%?,followed by the return way?30.61%?,and the single way?19.92%?.The deterioration of rocky desertification was mainly distributed in xiushan,pengshui and youyang,while the improvement of rocky desertification was mainly distributed in chongqing*,fengjie and wushan.The deterioration and improvement of rocky desertification was mainly distributed in the area where the elevation was 300800m.The mutual transformation of rocky desertification was complicated,but the area of different rocky desertification was decreased.The area of moderate rocky desertification decreased was the maximum?3046.75km2?,followed by severe rocky desertification?1254.56km2?,slight rocky desertification?691.56km2?,and extremely severe rocky desertification?229.19km2?.The change rate of rocky desertification increased firstly and then decreased.The rate of turn into rocky desertification decreased gradually;The rate of turn out from slight and extremely severe rocky desertification decreased gradually,while the rate of turn out from moderate and severe rocky desertification increased firstly and then decreased.The reduction of moderate rocky desertification was the maximum(50.78km2?a-1),followed by severe rocky desertification(20.91km2?a-1),slight rocky desertification(11.53km2?a-1),and extremely severe rocky desertification(3.82km2?a-1).The maximum rate of turn into rocky desertification occurred in slight rocky desertification(30.36km2?a-1),while the maximum rate of turn out from rocky desertification occurred in moderate rocky desertification(75.55km2?a-1).From 2001 to 2015,the rocky desertification's number of patches,diversity,evenness and aggregation decreased gradually,while the fragmentation,dominance,shape simplification and connectivity increased.The fragmentation and dominance of slight rocky desertification increased,while the number,shape simplification and aggregation decreased.The number,shape simplification and aggregation of moderate rocky desertification decreased,while the fragmentation and dominance increased.The number,fragmentation,dominance,shape simplification and aggregation of severe rocky desertification and extremely severe rocky desertification decreased.By analyzing the variation of vegetation coverage in Chongqing,the spatial and temporal variation law of vegetation and its influencing factors could be clearly understood,and further analyze the evolution characteristics of rocky desertification,which could provide some reference for the construction of ecological environment and the control of rocky desertification. |
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