Different biomass production and soil water patterns between natural and artificial vegetation along an environmental gradient on the Loess Plateau

Loess Plateau (LP) is a vulnerable and climate-sensitive ecoregion. With the implementation of "Grain for Green" project (GGP), the vegetation cover has largely improved, while the contradiction between overconsumption of soil water and sustainability of restored vegetation is increasingly prominent, and further threatening the ecosystem sustainability and socioeconomic development. Understanding the different responses of relations of biomass production and soil water regimes between natural and artificial vegetation along environmental gradient will be crucial for sustainability of restored vegetation on the LP. Here, aboveground biomass (AGB) and soil water content (SWC) of natural and artificial vegetation were measured in steppe, forest-steppe and forest zone from 2008 to 2017 on the Yanhe River catchment. The results showed that artificial vegetation consumed more soil water than natural vegetation in steppe and forest-steppe zone, while it did not over consume soil water in forest zone. The AGB of natural vegetation in forest zone was significantly higher than that in steppe and forest-steppe zone. Steppe zone had serious overload of artificial vegetation (overload ratio: 5.35), while no overload occurred in forest zone. So, we suggest a cessation of artificial vegetation expansion in steppe zone. In steppe zone, planting artificial vegetation increased competition intensity between AGB and SWC, and the relative benefit tended to be AGB, their competition intensity was the highest. In forest zone, the trade-off relationship between AGB and SWC had no significant difference between natural and artificial vegetation, and the competition intensity between the AGB and SWC was the weakest. Optimal vegetation restoration approach would maintain the balance between vegetation restoration and soil water. To obtain social and ecological sustainability on the LP, vegetation suitability and suitable management along different environmental gradients should be considered and identified in the future revegetation project.