Effectiveness of sawdust and straw mulching on postharvest runoff and soil erosion of a skid trail in a mixed forest

Loss of vegetation cover by forest harvesting has increased the average surface runoff volume and sediment yield in the Hyrcanian forest in Iran. Hence, treatments are needed to mitigate the effects of skidding operations on hydrological characteristics and sediment delivery into streams. The present study evaluated the efficacy of straw and sawdust mulches in reducing soil erosion relative to untreated control plots in a severely compacted loam soil area in the Hyrcanian forest during the first year after harvesting. Immediately after skidding operations, triplicate skid trail plots received straw mulch (16.5 kg m(-2)) sawdust mulch (2.8 kg m(-2)) or were left untreated for the control plots (8 m(2)). The experimental design was completely randomized; plots were randomly assigned to treatment, season, and leafless and leafed periods. The results of generalized linear modeling showed that season and treatment significantly affected the amount of runoff and sediment. Runoff was significantly lower in the summer than in the other seasons. Applying straw mulch to the skid trail decreased runoff by 36.5%, and sawdust mulch decreased runoff by 72.8% compared with the control. The straw and the sawdust mulch also decreased sediment yield by 51.9% and 94.9%, respectively. A regression analysis revealed that the runoff response to rainfall for all the treatments was linear. Also, the total measured runoff in all seasons after the straw and the sawdust mulch was less than the runoff of the control plots. However, the measured runoff in the leafless period was greater than in the leafed period. In the straw and the sawdust mulch, measured runoff in the leafless period was 91.7% and 89.8% of the total runoff, respectively. In the straw and sawdust treatment, 99.4% and 98.4%, respectively, of the sediment occurred in the leafless period. Covering the bare mineral, compacted soil on skid trails thus greatly reduces surface runoff and sediment yield.