Response of different understory grass configurations to soil erosion characteristics and its optimal configuration

As an important part of forest ecosystem, understory herbaceous vegetation plays an important role in regulating forest soil erosion. However, the effects of understory vegetation coverage (VCR) and its location on soil erosion are not fully understood. Therefore, this study established four kinds of VCRs (0 %, 30 %, 60 % and 90 %) and four vegetation configurations to study runoff and sediment yield under four rainfall intensities (45, 60, 90 and 120 mm/h), including: configuration A vegetation is concentrated on the upper slope, configuration B vegetation is concentrated on the downslope, configuration C vegetation is evenly distributed on the upper, middle and down slopes, and configuration D is based on a combination of configurations B and C, in which 10 % of the vegetation is transferred from the upslope to the downslope. The results showed that an increase of VCR effectively inhibited the generation of runoff and sediment, when the coverage of understory grass was 90 %, the benefits were most significant; Although increasing rainfall intensity led to higher runoff and sediment yield, the interception efficiency of grassland restoration did not decrease significantly; The runoff and sediment yields of the four vegetation configurations were lower than those of the bare land. Configurations C and D had the best inhibitory effects, and the downhill (configuration B) was better than the uphill (configuration A). Specifically, the average runoff and sediment reduction effects of configurations C and D were 1.85 and 1.82 times, 2.17 and 2.10 times, 1.65 and 1.47 times, and 1.93 and 1.69 times those of configurations A and B, respectively. In addition, linear regression shows that compared with vegetation coverage, altering vegetation configuration has a more significant effect on sediment regulation. In summary, understory vegetation restoration effectively inhibits soil erosion, and optimizing vegetation configuration further improves this result. It is recommends increasing herbaceous coverage combined with Configuration D to effectively mitigate understory erosion and enhance soil quality in Cunninghamia lanceolata pure forest within the red soil region of southern China.