## 4 Discussion
### The Variation in ESV in Different Landform Areas  
In terms of the same elevation position, the ESV per unit area was as follows: non-karst areas > pure-karst areas > semi-karst areas. The main reason for this is that the soil layer in the non-karst area is thick, which can meet the needs for growth of the various land vegetation. The purity of the soluble carbonate rock in pure-karst areas is high. During the soil forming process, the rock is weathered and dissolved in water, which makes is difficult for it to remain in place. The soil formed is thin, and the hydrothermal conditions and the vegetation growth environment is poor. The degree of dissolution in the semi-karst area is relatively light compared with that in the pure-karst area, and the soil that can meet the needs of plant growth can still be left in the landform development. However, due to strong human activities, the water and soil loss is intensified, and the ESV per unit area in semi-karst areas is the lowest.  
The ESV per unit area in non-karst areas > pure-karst areas > semi-karst areas for the same slope. The reason for this is that under the influence of the typical calcareous environment of karst, elements such as potassium, iodine, and sodium required for plant growth are quite scarce in the pure-karst area, which is extremely restrictive to plant growth. At the same time, the soluble salt content in pure-karst areas is high, the slope increases, the soil, water, and nutrient run-off happens more easily, resulting in rock desertification, and \"underground water rolling flow, surface water as expensive as oil\" is a true portrayal of the area [57]. In contrast, compared with the pure-karst areas, semi-karst and non-karst areas tend to have thicker soil layers with good water and fertility retention. The conditions of soil and water in non-karst areas are better than those in semi-karst areas, resulting in continuous soil cover and denser natural vegetation growth [49].  
The combined effects of human activities on land use through various socio-economic activities have caused changes in land-use patterns and structures, which affect the spatial and temporal distribution and changes in the regional ESV. Over the past 35 years, the population in Guizhou Province has increased by 8,843,300 people. The agglomeration effect of economic development has caused people to leave the countryside to increase their income, and has promoted the process of industrialization and urbanization. The urbanization rate increased from 9.3% in 1979 to 53.15% in 2020, resulting in dramatic changes in the land properties of each karst-landform-type area. The most obvious was the rapid increase in impervious land areas. For example, the impervious land in semi-karst areas increased by 353.03%, 94.79% of which is from cropland, with a decrease of USD 14 million in the cropland ESV. The impervious land in the non-karst areas increased by 287.54%, of which, 90.61% was provided by cropland, and the cropland ESV decreased by USD 10 million. The impervious land in the pure-karst area increased by 62,990.37 \(\mathrm{hm}^{2}\), of which, 91.24% was cropland, and the cropland ESV decreased by USD 34 million. Meanwhile, the increase in the impervious land area directly led to serious encroachment on ecological land; in addition, the decrease in the forest ESV in all periods of the three landform areas was more than USD 5 million.