Threshold effects of vegetation coverage on runoff and soil loss in the Loess Plateau of China: A meta-analysis

In the loess plateau, due to the vegetation recovery has achieved preliminary results, while it is controversial whether the vegetation cover can be increased unrestrictedly for a long time, thus defining the vegetation coverage threshold is gaining urgency. The purpose of this study was to define the vegetation coverage thresholds of runoff and soil erosion in the Loess Plateau, and quantify the effect of vegetation coverage changes on soil and water loss, and evaluate the effective vegetation coverage in different climatic regions. A total of 59 watersheds were involved in the meta-analysis, including 38 counties belonging to 6 provinces in the Loess Plateau. The vegetation coverage increased from 2.51% to 86.80%, the runoff modulus ranged from 155.7 to 780431.8 m3·km−2·a−1, and the soil erosion modulus ranged from 400 to 58285 t·km−2·a−1. Three specific vegetation coverage thresholds were identified for soil erosion: the lower threshold (0%–35%), the transition (35%–65%), and the upper threshold (65%–100%); four specific vegetation coverage thresholds were identified for runoff: the low threshold (0%–20%), the transition (20%–50%), the high threshold (50%–75%), and the upper threshold (75%–100%). In the Loess Plateau, the effective vegetation coverage in the cold and arid regions is 25.12%, in the semi-humid region is 51.02%, in the semi-arid region is 45.92%, and in the arid region is 26.53%, to which corresponding ecological management strategies should be adopted. Clarifying the impact of vegetation coverage on water and soil loss at the regional scale can provide insight into suitable management programs for the new pattern of runoff and soil erosion formed by the vegetation restoration in the Loess Plateau.