Runoff and soil erosion mitigation with sieved forest residue mulch strips under controlled laboratory conditions

• Published in: Forest ecology and management Vol. 396; pp. 102 - 112
• Main Authors: Prats, Sergio Alegre, Abrantes, João Rafael, Crema, Isabela P., Keizer, Jacob J., de Lima, João L.M.P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.07.2017
• Subjects: Connectivity; Forest residue; Mulch strips; Rill erosion; Soil erosion mitigation; Connectivity; Soil erosion mitigation; Rill erosion; Mulch strips; Forest residue
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/j.foreco.2017.04.019

•Sieved forest residue mulch was applied in strips at 50–70% cover in laboratory.•Mulch strips of 1/3 of the plot at 1Mgha−1, 70% cover reduced interrill erosion.•Mulch applied to the whole plot at 2.6Mgha−1, 50% cover reduced rill erosion.•Mulch strips can reduce off-site wildfire effects at low application costs.•Mulch applied to the whole area reduced both on-site and off-site wildfire effects. Post-fire forest residue mulching using eucalypt bark strands have been proven effective for reducing hillslope runoff and erosion in field plots of different sizes (0.25–100m2). Application rates of around 8–10Mgha−1 achieved about 80% protective soil surface. Lower application rates, however, would reduce costs and, possibly, allow faster application, which could be especially critical in late summer high-severity fires. Such lower rates could be achieved by applying less mulch per unit area, by applying mulch in specific zones (strips) and by removing the finest fractions, especially since these can be expected to contribute little to reduce erosion risk. The objective of this laboratory study was to identify the threshold, or the minimum application rate, at which a new mulch blend (without the fraction ≤4cm) would effectively control runoff and erosion. Two levels of ground cover by forest residue mulch (50 and 70%) and three mulch strips (covering the lower 1/3, 2/3 and 3/3 of a flume) were tested against the untreated bare soil by applying simulated rainfall and simulated inflow. The seven treatments were replicated three times using a 2.7m×0.3m flume with a 40% slope, filled with a dry loamy sand soil. Each experiment included: (i) a “Dry” soil run comprising 20min of simulated rainfall at a rate of 56mmh−1; (ii) a “Wet” soil run with the same rainfall characteristics; (iii) a “Flow” run combining 20min of rainfall with three inflows at increasing rates (52, 110, 232mmh−1) on nearly saturated soil. The results showed that overall runoff, interrill and rill erosion were strongly reduced and leaching was increased by covering the flume with 2m and 3m mulch strips at 70% ground cover (overall mulch application rates of 2.6 and 1.3Mgha−1). The 1m mulch strips at 70% mulch cover (1Mgha−1) also reduced significantly erosion but not runoff. The three mulch strips at 50% ground cover were less effective, and only the application over the whole plot was able to reduce interrill and rill erosion. Apparently, runoff depended most on mulch cover, while soil losses depended most on strip width. Even so, the new mulch blend was poorly effective in reducing runoff but effective in reducing interrill erosion and even highly effective in reducing rill erosion.