4.2 Drought loss resistance of different land covers
It is generally believed that higher land coverage might have led to a lower drought loss of karst dissolution. That means, in our study, the forest should have the lowest drought loss of karst dissolution, followed by shrubland and grassland, and then cropland should have the highest drought loss. However, the drought loss of karst dissolution for four types of land cover does not follow this law, especially the Site C. The results indicated that the land coverage is not the only reason for the drought loss resistance of karst dissolution. It should be the integrated result of multiple factors.
In principle, the higher the drought loss resistance, the lower the karst dissolution loss. Based on this principle, the study ranked the drought loss resistance of karst dissolution for four land cover types and shown in Figure 6. Totally, cropland in Site A has the highest drought loss resistance of karst dissolution, followed by forest and grassland, and shrubland has the lowest drought loss resistance of karst dissolution (Figure 6). The drought loss resistance of karst dissolution in Site B is similar to Site A, but the lowest drought loss resistance of karst dissolution is grassland (Figure 6). Surprisingly, the highest drought loss resistance of karst dissolution in Site C is grassland, followed by shrubland and forest, and cropland has the lowest drought loss resistance of karst dissolution (Figure 6).
As mentioned above, the drought loss resistance of karst dissolution is not only related to land coverage, but also the other factors. According to the data we measured (Table 4), soil pH may be, at least partly, the cause of the high drought loss of shrubland and grassland in Site A and Site B, while the drought loss resistance of karst dissolution in Site C may be related to soil organic matter. It must be noted that the available data can not completely clarify the actual reason for the drought loss difference of different land cover types. Nevertheless, a relatively straightforward qualitative result has an unmeasurable application for karst research and landscape protection, especially when considering afforestation to deal with climate change.