Afforestation May Not Be the Primary Choice for Vegetation Restoration in Agricultural Pastoral Ecotone of the Loess Plateau, China

Abstract

The artificial forests have caused greater soil water pressure in the agricultural pastoral ecotone. Understanding vegetation changes, soil water status and their interrelationships is crucial for sustainable development. In this study, fractional vegetation cover (FVC) in Yulin area was calculated for 2000 and 2020, and 23 sites were selected for soil and vegetation field investigations. The results showed that FVC increased from 0.11 in 2000 to 0.25 in 2020, but the spatial distribution of vegetation was uneven. The average gravimetric soil water content (GSWC) of 0–400 cm soil profile ranged from 2.8 to 12.3%. As the depth increases, the GSWC gradually decreased and stabilized at around 5.0%. All 23 sites had dried soil layer (DSL), the average formation depth of dried soil layer (DSLFD) was 162 cm, the average thickness of dried soil layer (DSLT) was 216 cm, and the average gravimetric soil water content of dried soil layer (DSL-GSWC) was 5.2%. In addition, Person correlation analysis indicated that GSWC shows a significant negative correlation with leaf area index (LAI), FVC and height of tree (H), and the DSLFD shows a significant positive correlation with H, diameter at breast height (DBH) and crown width (CW). In terms of species comparison, the highest GSWC was found in grasslands at 8.0%, followed by forests at 6.9%, and finally shrubs at 4.6%. As the climate becomes increasingly arid, the risk of artificial forest ecosystems will increase, and afforestation in the agricultural pastoral ecotone in the past may be unscientific. Perhaps herbaceous plants are more suitable for vegetation restoration, and afforestation is only carried out in some areas.