Impacts of different vegetation restoration options on gully head soil resistance and soil erosion in loess tablelands

Abstract

Vegetation restoration is identified as an effective approach to control soil erosion and affects soil detachment and resistance to concentrated flow on the Loess Plateau. However, the effects of vegetation restoration at gully heads in loess‐tableland remains unclear. This study was performed to investigate the effects of nine vegetation restoration types at gully heads on soil detachment rate (Dr) and soil resistance to concentrated flow (i.e. soil erodibility, Kr and critical shear stress, τc). Undisturbed soil samples were collected from nine vegetation‐restored lands and one slope cropland (as the control) and were subjected to a hydraulic flume to obtain Dr values of gully heads under six inflow discharges (0.5–3.5 L s‐1). The results showed that the Dr values of nine revegetated gully heads were 77.11% to 95.81% less than that of slope cropland, and the grassland dominated by Cleistogenes caespitosa and the shrubland dominated by Hippophae rhamnoides had a relatively greater decrease in Dr than those of other seven restoration types. The Dr value of nine revegetated gully heads could be better simulated by stream power than by flow velocity and shear stress and was also significantly affected by soil disintegration rate (positively), soil bulk density, saturated hydraulic conductivity, organic matter content, and water‐stable aggregate stability (negatively). Additionally, roots with diameters of 0 to 0.5 mm showed a greater effect on Dr than those with larger diameters. Compared to cropland, the nine restored types reduced Kr by 76.26% to 94.26% and improved τc by 1.51 to 4.68 times. The decrease in Kr and the increase in τc were significantly affected by organic matter content, water‐stable aggregate, mean weight diameter of aggregate and root mass density. The combination of grass species (Cleistogenes caespitosa) and shrub (Hippophae rhamnoides) could be considered the best vegetation restoration types for improving soil resistance of gully heads to concentrated flow. © 2019 John Wiley & Sons, Ltd.

Variations in Soil Erosion Resistance of Gully Head Along a 25-Year Revegetation Age on the Loess Plateau

“…These efforts also effectively stabilized the gully heads and thus contained the gully headcut erosion [33]. At present, the annual soil erosion module is effectively controlled at the level of 2440 t km −2 a −1 in the study area, and the vegetation communities comprise mainly planted forests and shrubs and native secondary herbaceous plants [21].…”

“…During our investigation of gully heads, some cracks developed near gully heads. Kompani-Zare et al [39] and Guo et al [21] stated that soil samples from 0 to 30 cm depth near the gully heads (the distance was less than 5 m) can represent soil properties of the gully heads. Therefore, in consideration of collapsibility and vertical joints development of loess, the sampling plots were established about 1.0 m meters from gully heads to ensure safety.…”

“…The improvement of soil erosion resistance by revegetation is mainly controlled by the combination of soil properties and root traits [15][16][17][18]. In terms of soil properties, many studies have verified that the revegetation significantly affects soil erosion by changing the soil bulk density, organic matter content, and water-stable aggregate [19][20][21]. Furthermore, the vegetation root zone is the dynamic interface of soil-plant-atmosphere continuum in partitioning rain and irrigation water into evaporation, transpiration, runoff, and deep drainage [22,23], but is also the home of "green water" which is the source of plant nutrition [24].…”

“…Moreover, root growth can bind and bond soil particles and aggregate, thus, enhances soil resistance to erosion [28]. Some root parameters, for example root biomass, length density, and surface area density, were used to estimate the effect of root on soil detachment [21,[28][29][30][31]. De Baets and Poesen [25] found that soil detachment rate reduced exponentially with increasing root biomass.…”

“…The gully headcut erosion by concentrated flow became the main sediment resource. At present, the gully headcut erosion was controlled effectively due to the implementation of a series of control measures (e.g., the "Three Protection Belts" and the "Green for Grain" project), which, to some extent, was attributed to the fact that the revegetation improves the soil resistance of gully heads to concentrated flow [21,33]. Since some ecological restoration projects were conducted, land use has changed dramatically in the Loess Plateau [34].…”