Comparative Effectiveness of Different Mulch Types and Application Rates for Reducing Runoff and Sediment Yield on Forest Skid Trails

ABSTRACT Rehabilitation of skid trails following timber harvesting is critical for preserving forest soil integrity, particularly within ecologically sensitive ecosystems such as the Hyrcanian forests of northern Iran, a UNESCO World Heritage Site. Although mulching is widely recommended for erosion control, field evidence comparing different locally available organic mulches across multiple application rates on real skid trails under natural rainfall remains limited. This 13‐month field study addressed this gap by quantifying event‐based surface runoff and sediment yield from skid trails treated with three natural mulches: sawdust (SDM), rice straw (RSM), and leaf litter (LLM), each applied at low, medium, and high rates (2.22/4.44/6.66, 0.38/0.76/1.14, and 0.62/1.22/1.86 kg m −2 , respectively). A total of 33 bounded runoff plots were established, including nine mulch type–rate combinations, untreated skid trail controls, and undisturbed forest controls, each replicated three times. Runoff and sediment were measured after each runoff‐producing rainfall event. Using linear mixed‐effects models with rainfall treated as a continuous predictor, we evaluated treatment‐specific rainfall sensitivity for both runoff and sediment yield. Runoff was primarily controlled by rainfall amount ( F = 49.31, p < 0.001), with no significant overall treatment effect after accounting for rainfall. Mean runoff values were 22%–46% lower in mulched plots than in untreated skid trails, but these reductions should be interpreted as descriptive tendencies rather than statistically robust treatment effects. In contrast, sediment yield exhibited a significant rainfall × treatment interaction ( F = 11.94, p < 0.001). Untreated skid trails produced substantially more sediment (0.65 g m −2 event −1 ) than undisturbed forest plots (0.08 g m −2 event −1 ), whereas mulching reduced sediment yield by 45%–87%. The strongest sediment reductions were achieved with high‐rate sawdust (6.66 kg m −2 ) and rice straw (1.14 kg m −2 ), which reduced rainfall–sediment sensitivity to levels comparable with undisturbed forest soils. Their superior performance was likely related to more persistent ground cover, greater raindrop interception, and increased surface roughness compared with leaf litter mulch, particularly at low application rates. These results indicate that mulching primarily controls erosion by limiting sediment detachment and transport, rather than by fully restoring runoff dynamics on compacted skid trails. Because sawdust and rice straw are locally available forestry and agricultural residues, the identified rates represent practical and potentially operationally feasible benchmarks for skid trail rehabilitation, although site‐specific costs and logistics should be evaluated before large‐scale application.