Upper Limit Of Yuanmou Dry-hot River Valley From Vegetation-soil Perspective

The most important reason for the formation of dry-hot river valley is the redistribution of surface water and heat relationship along the elevation caused by the strong variation of topographic factors.At present,there are many shortcomings in the methods of determining the boundary of dry-hot river valley based on the distribution of vegetation types,such as shrub shrub,and these classifications generally lack the support of measured data.Therefore,in this study,remote sensing technology was used to obtain the distribution range of different vegetation types in Yuanmo dry-hot valley,and field investigation combined with laboratory analysis was used to analyze the typical vegetation and soil particle size,soil p H value,soil moisture content,water-soluble salt and other indicators of different altitude gradients.Based on the vegetation-soil relationship,distribution limits and ranges of dry-hot valley were defined.To provide data support for scientific management of vegetation and soil resources.The following conclusions are obtained:(1)By combining field survey sampling data with GF-2 remote sensing images,supervised classification and decision tree classification were used to extract the distribution ranges of different vegetation types in Yuanmou dry-hot Valley.The results are as follows: the main cultivated land is distributed in the low altitude area below 1350 m,the Yunnan pine and other trees are mostly distributed in the altitude area of 1800-2000 m,and the shrub communities are mostly distributed in the altitude area of 1700-1800 m.The shrub was mostly distributed in the area of 1500-1700 m above sea level.(thin irrigation)grassland was mostly distributed in the area of1100-1500 m above sea level.(2)The soil physical properties of different altitudinal gradients were analyzed.The results showed that the soil particle size in the study area was mainly divided into silt with a content of more than 45%,while the soil particle size composition of different altitudinal gradients ranked silt > clay > sand in order of volume proportion.The characteristics of soil particle size parameters in different soil layers with different altitude gradients are as follows: the particle size is coarser,the sorting is poor,the skewness is generally positive and the peak state is moderately sharp.The soil moisture content is higher at 1900 m above sea level and lowest at 1500 m above sea level.(3)By exploring the soil chemical properties of different elevation gradients in Yuanmou.The results showed that the p H of the soil at different elevations in the Dongshan-Xishan Mountains of Yuanmou was weakly acidic,and the p H value decreased with the increase of soil depth.In Dongshan District,the p H value of soil surface reaches the maximum at 1900 m and 1700 m above sea level.However,in the distribution area of 1900 m and 1500 m in the west Mountains,the p H value of soil is generally higher than that of other elevations.The content of water soluble salt in soil is mainly composed of bicarbonate ions,and the highest content of water soluble salt in soil occurs at the altitude of 1700 m in Dongshan and 1500m-1900 m in Xishan.(4)Correlation analysis of soil particle size and soil water content,soil p H and water-soluble salt under different altitudinal gradients showed that the correlation between particle size distribution and soil water content under different altitudinal gradients in the west Mountain was more significant than that in Dongshan.However,the correlation between soil p H and water-soluble salt content was not significant at the altitude of 1900m-1800m(P≤0.01),but was extremely significant at the altitude gradient of 1500m-1600m(P≤0.01).(5)Affected by hot and dry climate and topography,vegetation types and soil physicochemical properties in the study area show distinct particularities.The main vegetation types ranged from low altitude to high altitude,from xerophyte grassland or shrub shrub(East Mountain elevation: 1100-1600m;West Mountain elevation:1000-1500m)to shrub shrub(East Mountain elevation: 1600-1700m;West Mountain elevation: 1500-1600m)to low tree shrub(East Mountain elevation: 1700-1800m;Xishan 1600-1700m)--evergreen coniferous broad-leaved mixed forest or deciduous broad-leaved forest(Dongshan >1800m,Xishan >1700m)in the transition zone distribution;However,the content of water-soluble salt in Dongshan at 1700 m is higher than that in other elevations.The highest water soluble salt content was found in the soils of the West Mountains at the altitudes of 1900 m and 1500 m.Along the elevation gradient,the soluble salt content of soil increased first and then decreased.The soluble salt content of soil profiles at different elevations showed a surface-aggregation phenomenon and increased first and then decreased in different depths of soil layers.In conclusion,based on comprehensive topography,vegetation cover and soil properties,the upper limit of Yuanmou dry-hot valley can be determined as a ring transition zone composed of Dongshan 1600-1700 m and Xishan1500-1600 m.