Abstract
Forest operations often enhance runoff and soil loss in roads and skid trails, where cut slopes and fill slopes are the most important source of sediment. This study evaluated the effectiveness of four erosion control treatments applied to cut slope and fill slope segments of forest roads of different ages in the Hyrcanian forest in northern Iran. The treatment combinations, each replicated three times, included four classes of mulch cover (bare soil [BS], wood chips cover [WCH], sawdust cover [SC], and rice straw cover [RSC]), two levels of side slope (cut slope and fill slope), two levels of side slope gradient (20–25% and 40–45%), and three levels of road age (three, 10 and 20 years after construction). Mulch cover treatments significantly reduced average surface runoff volume and sediment yield compared to BS. Regardless of erosion control treatment, greater surface runoff volume and soil loss under natural rainfall occurred on steeper slope gradients in all road age classes and decreased with increasing road age on both slope gradients. On cut slopes, average runoff and soil loss from the plots covered with WCH (17.63 l per plot, 2.43 g m–2) was lower than from those covered with SC (22.81 l per plot, 3.50 g m–2), which was lower than from those covered with RSC (29.13 l per plot, 4.41 g m–2 and BS (34.61 l per plot, 4.94 g m–2). On fill slopes, average runoff and soil loss from the plots covered with WCH (14.13 l per plot, 1.99 g m–2) was lower than from plots covered with SC (20.01 l per plot, 3.23 g m–2), which was lower than from plots covered with RSC (24.52 l per plot, 4.06 g m–2) and BS (29.03 l per plot, 4.47 g m–2). Surface cover successfully controlled erosion losses following road construction, particularly on steep side slopes with high erosion potential.
Highlights
Forest roads and skid trails can significantly increase surface runoff and sediment yield, especially when bare soils are exposed to high traffic frequency or when the bearing capacity of the soil is exceeded and rutting occurs (Swift and Burns 1999, McBroom et al 2008, Solgi et al 2014)
On both types of side slope and for all mulch cover types and road ages, the amounts of runoff and soil loss increased consistently with increasing slope gradients, with greatest amounts observed on cut slopes on bare soils on gradients of 40–45%, and smallest amounts observed on fill slopes covered with wood chips on gradients of 20–25%, regardless of road age
The effectiveness of mulch treatments is primarily due to providing ready ground cover in the form of mulch, which stabilizes the soil by providing protection from the impact of rainfall, reducing overland flow velocity through increased surface roughness
Summary
Forest roads and skid trails can significantly increase surface runoff and sediment yield, especially when bare soils are exposed to high traffic frequency or when the bearing capacity of the soil is exceeded and rutting occurs (Swift and Burns 1999, McBroom et al 2008, Solgi et al 2014). As forest roads constitute the basic infrastructure for forest management activities (Hacisalihoğlu et al 2019), potential environmental problems, such as increased surface runoff and soil erosion following heavy rainfall (Ziegler et al 2004) that arise following forest road construction and use mandate, require protective measures that are either. One of the main impacts of forest road construction is the formation of steep, bare roadside slopes (Liu et al 2014, Cerdà 2007). Lack of protective surface cover and bare roadside slopes can generate significant amounts of soil loss during the rainy season (Arnáez et al 2004, Jordán-López et al 2009, Bochet et al 2009). To prevent or at least reduce surface runoff and roadside slope erosion, the use of soil protective
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