The effectiveness of mulching practices on water erosion control: A global meta-analysis

Mulching is widely recognized as an effective soil and water conservation measure all over the world. Nevertheless, a comprehensive evaluation of mulching's effectiveness in controlling soil erosion and the influencing factors is still lacking. A global meta-analysis based on 421 runoff and 512 soil loss observations from 90 publications was conducted to evaluate the effectiveness of mulching in reducing runoff and soil loss across a variety of variables (i.e. mulch type, mulch coverage and application rates, rainfall intensity, land use, soil texture, slope gradient, and slope length). Our meta-analysis shows that overall, mulching significantly reduced runoff and soil loss by 47.4% and 76.2%, respectively. Straw mulch and wood-based mulch are generally more effective in reducing runoff and soil loss than rock fragments, highlighting the effectiveness of organic materials in controlling water erosion. In general, increasing mulch coverage and application rates resulted in a significant reduction in runoff and soil loss. It is recommended, however, that mulch coverage should be at least 60% based on the trade-off between economic costs and ecological benefits, which can reduce runoff and soil loss by approximately 50% and 80%, respectively. An application rate of 0.3–0.4 kg m−2 for straw and 0.6–0.8 kg m−2 for wood-based mulch should be sufficient to effectively control soil erosion. The study also found that mulching is more effective in post-fire forests on medium-textured soils and less effective on steep slopes (>60%) and under both natural and simulated extremely heavy rainfall conditions (>90 mm/h). Overall, this study provides further insights into the impact of mulching on water erosion globally and proposes an overall framework for a precision mulching strategy (P-M-S) to guide the implementation of mulching in soil erosion control

Effects of Simulated Gravel on Hydraulic Characteristics of Overland Flow Under Varying Flow Discharges, Slope Gradients and Gravel Coverage Degrees

To quantify the hydraulic characteristics of overland flow on gravel-covered slopes, eight flow discharges (Q) (8.44-122 L/min), five slope gradients (J) (2 degrees-10 degrees) and four gravel coverage degrees (Cr) (0-30%) were examined via a laboratory flume. The results showed that (1) gravel changed flow regime. Gravel increased the Reynolds number (Re) by 2.94-33.03%. Re were less affected by J and positively correlated with Cr and Q. Gravel decreased the Froude number (Fr) by 6.83-77.31%. Fr was positively correlated with Q and J and negatively correlated with Cr. (2) Gravel delayed the flow velocity (U) and increased the flow depth (h) and flow resistance (f). Gravel reduced U by 1.20-58.95%. U was positively correlated with Q and J and negatively correlated with Cr. Gravel increased h by 0.12-2.41 times. h was positively correlated with Q and Cr and negatively correlated with J. Gravel increased f by 0.15-18.42 times. f were less affected by J, positively correlated with Cr and negatively correlated with Q. (3) The relationships between hydraulic parameters and Q, J and Cr identified good power functions. Hydraulic parameters were mainly affected by Cr. These results can guide the ecological construction of soil and water conservation

Mechanism Underlying the Spatial Pattern Formation of Dominant Tree Species in a Natural Secondary Forest

<div><p>Studying the spatial pattern of plant species may provide significant insights into processes and mechanisms that maintain stand stability. To better understand the dynamics of naturally regenerated secondary forests, univariate and bivariate Ripley’s <i>L(r)</i> functions were employed to evaluate intra-/interspecific relationships of four dominant tree species (<i>Populus davidiana</i>, <i>Betula platyphylla</i>, <i>Larix gmelinii</i> and <i>Acer mono</i>) and to distinguish the underlying mechanism of spatial distribution. The results showed that the distribution of soil, water and nutrients was not fragmented but presented clear gradients. An overall aggregated distribution existed at most distances. No correlation was found between the spatial pattern of soil conditions and that of trees. Both positive and negative intra- and interspecific relationships were found between different DBH classes at various distances. Large trees did not show systematic inhibition of the saplings. By contrast, the inhibition intensified as the height differences increased between the compared pairs. Except for <i>Larix</i>, universal inhibition of saplings by upper layer trees occurred among other species, and this reflected the vertical competition for light. Therefore, we believe that competition for light rather than soil nutrients underlies the mechanism driving the formation of stand spatial pattern in the rocky mountainous areas examined.</p></div

Mechanism Underlying the Spatial Pattern Formation of Dominant Tree Species in a Natural Secondary Forest - Fig 1

<p>Spatial distributions of trees of different DBH classes (small (a), medium (b), large (c)) and height classes (sapling (d), medium (e), tall (f)).</p

Effect of rock fragment cover on nutrient loss under varied rainfall intensities : A laboratory study

Surface rock fragments retard overland flow discharge, reduce the runoff generation rate and soil erosion as well as nutrients loss. In Northwest China, a common method for minimizing water, soil, and nutrient losses is the use of rock fragment cover. We used lab stimulation testing to evaluate rock fragment cover efficacy for nutrient conservation. Nutrient losses were determined in both the runoff and sediments under three rain intensities (30, 60 and 90 mm·h1), four rock fragment covers (0, 10, 20 and 30%) and a slope of 10. The results showed that rock fragment cover significantly reduced the nutrient losses. Compared with the bare soil control, the rock fragment cover reduced the runoff volume and sediments by 18-38 and 11-69%, respectively, and reduced N and P losses by 9-43 and 16-70%, respectively. These results indicate that rock fragment cover is an effective method for reducing land degradation and improving local environmental conditions

Univariate analyses of trees of different DBH classes.

<p>Univariate functions <i>L</i>(r) (dotted lines) are shown with the simulation intervals (shadow areas). L: large (DBH = 1-15cm); M: middle (DBH = 15-30cm); S: small (DBH> = 30cm).</p

Statistics of trees in each DBH and height interval and the corresponding relationship between DBH and height (embedded) for the four dominant species.

<p>Statistics of trees in each DBH and height interval and the corresponding relationship between DBH and height (embedded) for the four dominant species.</p

Characteristics of the four dominant species in the secondary forest within the survey area covering 4ha.

<p>Characteristics of the four dominant species in the secondary forest within the survey area covering 4ha.</p

Bivariate analyses exploring the association of intra- and interspecies relationships between trees of different height ranks.

<p>The classification of height classes was the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0152596#pone.0152596.g004" target="_blank">Fig 4</a>. U: upper layer, M: middle layer; S: sapling. Grey bars: repulsion; yellow bars: attraction; void: independence.</p

Spatial distribution of soil physical and chemical indices.

<p>Spatial distribution of soil physical and chemical indices.</p