DOI: 10.5061/dryad.547d7wm4r
title: Trade-off between vegetation type, soil erosion control and surface water in global semi-arid regions: A meta-analysis

description: Soil erosion control and water resource protection can closely interact
 during restoration of terrestrial ecosystems. In semi‐arid ecosystems, an
 urgent issue is how vegetation restoration can achieve the goal of soil
 erosion mitigation and water conservation, which in turn, feeds back to
 ecosystem functioning. We reviewed 78 articles from 22 countries in
 semi‐arid areas to evaluate the effects of vegetation type (i.e. forest,
 grassland and scrubland) on runoff and sediment yields across different
 environmental conditions (i.e. vegetation coverage, rainfall intensity,
 slope gradient and soil texture). Our meta‐analysis shows that runoff and
 sediment reduction both increased as the vegetation coverage increased,
 and tended to be stable when vegetation coverage exceeded 60%. Vegetation
 provided a greater benefit for sediment reduction than for runoff control
 under intense rainfall. Grasslands were generally more effective in
 reducing sediment than other vegetation types. Forests, grasslands and
 scrublands were most efficient in soil erosion control on 20°–30°, 0°–25°
 and 10°–25° slopes respectively. Grasslands and scrublands generally
 performed better with respect to soil erosion control on moderately coarse
 soils, whereas forests were most effective on medium‐textured and
 moderately fine soils. Synthesis and applications. Effective restoration
 and soil erosion control in semi‐arid ecosystems strongly depends on the
 selection of vegetation type. Our study further indicates that, for land
 managers, it is critical to consider local slope, and soil texture, and
 maintain appropriate vegetation coverage to achieve ecosystem
 sustainability. Grasslands might be particularly suitable to optimize the
 trade‐off between soil erosion control and surface water resource in
 semi‐arid regions.
description: Data collection and compilation To compare
 the efficiency of vegetation in controlling soil erosion, we used the Web
 of Science and Google Scholar search engines to identify peer‐reviewed
 journal articles on these topics between 1965 and 2017. The search
 included either “runoff”, “sediment” or “soil erosion”, and either
 “semi‐arid” or “semiarid”, resulting in 4,625 publications. To avoid
 publication bias, the primary criteria for the data compilation were as
 follows: (a) the aridity index: precipitation (mm)/potential
 evapotranspiration (mm) at the study site must be &lt;0.5; (b) at
 least one of the relevant vegetation types (i.e. forest, grassland and
 scrubland) and a control (bare land or farmland) representing soil erosion
 without vegetation; (c) the same variables (runoff or sediment) were
 measured in both the control and vegetated plots; and (d) the mean values,
 number of replicates and variances for each data pair were reported. In
 total, 78 publications fulfilled these criteria, and a list of data
 sources used in the study is provided in the Data sources section (see
 Appendix Table S1; Wu et al., 2020). From each study,
 the mean values of the soil erosion response variables and their
 corresponding variance and the number of replicates were extracted
 directly from the text or tables, or from figures using GetData Graph
 Digitizer 2.24 software or estimated from the median, range and sample
 size (Hozo, Djulbegovic, & Hozo,2005 ). Other data, such as mean
 annual rainfall, mean annual temperature, mean annual evapotranspiration,
 vegetation coverage, rainfall intensity, study scale, slope and soil
 texture, were also extracted from the publications. Other factors
 affecting soil erosion processes, such as the amount of rainfall, were not
 used in this meta‐analysis due to an insufficient number of papers
 reporting these variables. Soil erosion and runoff were
 measured primarily using natural and simulated rainfall, but four studies
 involved model estimation and fallout radionuclide techniques. The study
 scale ranged from 0.0625 m2 to 16.8 ha, with most studies focussing on
 areas smaller than 100 m2. The mean annual temperatures of the study sites
 included in the meta‐analysis ranged from 6.3 to 29.7°C. The mean annual
 rainfall ranged from 180 to 970 mm, and the mean annual evapotranspiration
 from 290 to 2,500 mm. Most studies were conducted in China and Spain;
 other areas represented in this meta‐analysis included the USA and
 Australia (Figure 1 ). Little information was available for large areas of
 Africa and South America. However, we believe that our results are
 applicable to most semi‐arid regions because of the inclusion of data from
 varied sources. The vegetation types included forests,
 grasslands and scrublands as reported in the original study (Table 1).
 Forest refers to natural vegetation or plantations with a dominance of
 trees (canopy density &gt; 20%). Grassland refers to artificial
 grassland or natural grassland. Scrubland refers to a plant community
 characterized by vegetation dominated by shrubs, often also including
 grasses and forbs. Soil texture was classified into five categories
 (coarse, moderately coarse, medium, moderately fine and fine) according to
 the Soil Science Division Staff (2017) and Elias et al. (2018). The slope
 gradients were divided into the following eight categories: 0°–5°, 5°–10°,
 10°–15°, 15°–20°, 20°–25°, 25°–30°, 30°–35°, and &gt;35°.