Regional variation in soil water and vegetation characteristics in the Chinese Loess Plateau

Soil water is the limiting factor that determines ecosystem development in arid and semi-arid regions. Thus, determining the relationships between soil water and vegetation can inform the restoration of vegetation and water resource management. However, these relationships have not been fully investigated at the regional scale. In this study, field observations were conducted in two typical vegetation zones of the Loess Plateau of China: forest-steppe and semi-arid steppe zones. Variation in soil water content (SWC) and vegetation characteristics (plant density and species richness) in addition to their correlations were analyzed in grasslands and forestlands (occupied by black locust) in each zone. SWC, plant density, and species richness in the forest-steppe zone were significantly higher than those in the semi-arid steppe zone (p < 0.01). Plant density and species richness were positively correlated with SWC in both zones (all the correlation coefficients were higher than 0.7). Thus, higher soil water resources could support more plants of varied vegetation types. Moreover, plant density and richness could be important indices that reflect soil water vegetation carrying capacity at the regional scale. SWC, plant density, and species richness of the forestlands all significantly decreased in the two zones, indicating that continuous loss of soil water may lead to the degradation of afforestation. Notably, these trends all exhibited increasing trends in grasslands as restoration length increased in the forest-steppe zone, but exhibited decreasing trends in grasslands of the semi-arid steppe zone. Consequently, grasslands may be a more sustainable ecosystem type in this region. Taken together, these results indicate that both vegetation types and plant density should be taken into consideration when planning vegetation restoration in arid and semi-arid regions in order to promote long-term soil water conservation.