Study On The Correlation Between Vegetation Cover And Soil Organic Matter In Longchuanjiang Watershed

The loss of soil organic matter(SOM)not only results in the decrease of land productivity,but also exacerbates the trend of global warming to some extent.Nowadays,the loss of SOM has attracted more and more attention in the study of soil erosion and its control.What's more,as an important factor affecting soil erosion,vegetation plays a key role in control the soil organic matter loss.This paper mainly used 3S technique and landscape pattern index method to study the relationship between vegetation cover change,landscape pattern evolution and temporal and spatial variation of soil organic matter content in Longchuanjiang Watershed from 1982 to2016.The main findings showed that:1.Vegetation cover and its change(1)Vegetation cover area and dynamic changeThe vegetation types in the study area mainly include warm coniferous forest,semi-humid evergreen broad-leaved forest,warm limestone thickets,and dry heat sparse tree shrub bush.From 1982 to 2016,warm coniferous forests and warm limestone shrubs as well as dry land area showed a decreasing trend,and the area with the largest decrease was warm coniferous forest.Semi-humid evergreen broad-leaved forest,artificial forest,dry heat sparse tree shrub bush,paddy field,water area and residential area increased constantly,but the water area didn't increase obviously.The largest dynamic degree of vegetation cover was the artificial forest,which was 3.83%/a,and the change range was the largest,reaching 130.13%and the area increased by183.29 km~2.On the contrary,the smallest dynamic degree of vegetation cover were dry heat sparse tree shrub bush and water area,respectively 0.39%/a and 0.37%/a,besides,they both with a slight increase of 13.41%and 12.48%respectively.(2)Landscape pattern changeOn the whole,the degree of aggregation of the Longchuanjiang Watershed landscape was reduced,the degree of fragmentation was deepened,the integrity was impaired,and the dominance is reduced.What's more,the connectivity of the landscape continued to decrease as its plaque increased.The patch shape of warm temperate coniferous forest and evergreen broadleaved forest was very complex and irregular,while the patch shape of water area and artificial forest was relatively simple.2.Soil organic matter and its change(1)Through comparative analysis of soil organic matter content in 1982 and2016,it was found that the soil organic matter content in Longchuanjiang Watershed has generally decreased in the past 34 years,and only in some areas has the soil organic matter content increased.In 1982,the high soil organic matter content(6.62%~7.17%)in the Longchuan River Basin was mainly distributed in the southwestern part,while the low value area(0.65%~1.65%)was mainly distributed in the northeast of the Longchuanjiang Watershed.The southwestern part of the study area was dominated by warm coniferous forests,and the vegetation cover was less disturbed by humans.The northeastern part was mainly composed of warm limestone thickets and dry and dry heat sparse tree shrub bush.It was also very large and was greatly affected by human activities.Secondly,due to deforestation and excessive reclamation,the soil was poor and the organic matter content was reduced.The increase in SOM in some areas was due to the implementation of measures such as returning farmland to forests and closing hillsides for afforestation.In 2016,the high soil organic matter content in the Longchuanjiang Watershed was only distributed sporadically,and the area occupied was not large.The low-value areas in the basin mainly accounted for the majority.In general,the area of high-value areas in the entire basin is much larger than the area of low-value areas.(2)According to the spatial distribution data of SOM in different administrative regions of Longchuanjiang Watershed,the high organic matter content area(6.62%~7.17%)was mainly distributed in Dayao County and Luding County in 1982,while the 2016 soil organic matter high value area only occupied a small part of Yao'an County and Yuanmou County,the low-value area(0.65%~1.65%)was mainly distributed at the junction of Nanhua County,Dayao County and Yongren County and Luding County.The main reason for this change was Dayao County and Mou Ding County was relatively rapid development.Compared with other administrative areas,the economic level was relatively high,the rapid development of social economy derived from a variety of needs.The increase of soil organic matter content in some areas of Yuanmou County and Yao'an County was due to the effective measures of returning farmland to forest and closing mountains for forest cultivation,and the improvement of vegetation cover.3.Correlation characteristics between vegetation cover and organic matter changeThe change of soil organic matter content was closely related to different vegetation cover types.In 1982,the highest content of soil organic matter was warm coniferous forest,followed by semi-humid evergreen broad-leaved forest.Compared with 1982,the soil organic matter content of warm coniferous forest decreased from3.91%to 2.435%,and the soilo organic matter content of artificial forest decreased from 7.79%to 1.91%.The content of soil organic matter in semi-humid Semi-humid evergreen broad-leaved forest increased from 3.3%to 4.93%,and the content of soil organic matter in warm limestone thickets increased from 1.20%to 7.96%.However,the content of soil organic matter in dry land,paddy field and dry heat sparse tree shrub bush did not change much.From the point of view of soil organic matter content,the content of soil organic matter in dryland and paddy field was far lower than that in woodland.When the warm coniferous forest was changed to dry land,the dry land was changed to paddy field,and the semi-humid evergreen broad leaved forest was converted into artificial forest,the soil organic matter content in the Longchuanjiang Watershed was continuously reduced.