Abstract
Ground-based skidding operations can lead to soil compaction and displacement, which could cause negative effects on forest soil. Hence, some efforts such as forestry best management practices (BMPs) must be implemented in the prone area to mitigate these possible impacts. Several materials and treatments have been adopted to suppress these adverse effects by increasing the ground cover. However, the effects of mulch treatments on runoff and sediment yield are inconclusive with a diverse range of effectiveness. For these reasons, in this research mulch treatments were tested as to determine how the application of organic mulch amendments such as straw and leaf litter and contour-felled logs would alleviate the runoff and sediment yield on machine operating trails and ensure successful hillslope stabilization. The aims of the study were to analyse and compare the effectiveness of leaf litter (LM) and straw mulch (SM) rate and different distances of contour-felled logs (CFL) to mitigate the runoff and sediment yield, and examine the impact of rainfall intensity on effectiveness of litter mulch, straw mulch, and contour-felled logs. Totally, 30 bounded runoff plots in the machine operating trails and four treatments including litter mulch (LMR1: 0.62, LMR2: 1.24, and LMR3: 1.86 kg m-2), straw mulch (SMR1: 0.45, SMR2: 0.92, and SMR3: 1.34 kg m-2), contour-felled logs (CFL10: 10, CFL20: 20, and CFL30: 30 m), and untreated area were established in triplicate with 4 m width and 100 m length. During the study period, the runoff and sediment yield in the untreated trails (U) were 2.36 mm and 11.84 g m-2. Straw (from 41.5 to 60.6%) and litter mulch (from 38.1 to 55.1%), and contour-felled logs treatments (from 70.8 to 88.1%) significantly decreased the runoff, compared to U treatment. Results show that mulch treatments with three different levels of Litter Mulch Rate, LMR1, LMR2, and LMR3 decreased mean sediment by 46.6, 64.0 and 71.8%, in the treatments with three different levels of Straw Mulch Rate, SMR1, SMR2, and SMR3 decreased mean sediment by 42.9, 62.1, and 69.9%, and in the treatments with three different distances of Contour-Felled Logs, CFL10, CFL20, and CFL30 decreased mean sediment by 90.6, 94.7 and 88.3% comparing to U, respectively. The relationships of the runoff and sediment responses to increasing mulching rate of litter and straw followed as negative logarithmic curves, but the decreasing-increasing trends were observed in runoff and sediment yield as the distance between contour-felled logs increased from 10 to 30 m. Polynomial regression equations were developed for predicting the runoff and sediment yield as a function of the application rate of litter and straw mulch and the distance between contour-felled logs, and rainfall intensity. We concluded that contour-felled logs treatment was more effective than both litter and straw mulch to mitigate the runoff, runoff coefficient, and sediment yield on machine operating trails. As a management measure, it could be possible to propose that the contour-felled logs with a distance of 20 m be prescribed to protect the machine operating trails from the negative effects of surface waterflow.
Highlights
Ground-based skidding operations by forestry machines can lead to soil compaction and displacement, which could cause negative hydrological and physical effects on forest soil depending on forest site characteristics (Picchio et al 2019), silvicultural treatment (Picchio et al 2016) and forest logging typologies and quality (Hansson et al 2018, Jourgholami et al 2019a)
Our study demonstrated that the effects of three post-harvest rehabilitation treatments can be effective to mitigate surface runoff and sediment yield under the natural conditions on the machine operating trails
Our findings revealed that contour-felled logs with different distance were found to be more effective than the litter and straw mulch to reduce runoff, runoff coefficient, and sediment yield compared to untreated treatment
Summary
Ground-based skidding operations by forestry machines can lead to soil compaction and displacement, which could cause negative hydrological and physical effects on forest soil depending on forest site characteristics (Picchio et al 2019), silvicultural treatment (Picchio et al 2016) and forest logging typologies and quality (Hansson et al 2018, Jourgholami et al 2019a). Several materials and treatments have been adopted to suppress the adverse effects of ground-based skidding operations including mulches and seeding by increasing the ground cover (Jourgholami and Etehadi Abari 2017). Other alternatives, such as log erosion barriers (contour-felled logs) are installed to decrease the erosive power of runoff, increase the infiltration rate, store the eroded materials, and reinforce and stabilize the hillslopes (Wagenbrenner et al 2006, Kim et al 2008, Robichaud et al 2008a). Mulch treatments by coverage of the soil surface can absorb the kinetic energy of raindrops, reduce splash erosion and soil detachment, decrease the transport capacity of eroded sediment, alleviate temperature fluctuations, and enhance infiltration rate (Robichaud et al 2008a, Jordán et al 2010)
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