This study examined the relative impact of hikers, horses, motorcycles, and off-road bicycles in terms of water runoff and sediment yield from 108 sample plots on existing trails in or near Gallatin National Forest, Montana. A modified Meeuwig drip-type rainfall simulator was used to reproduce natural rainstorm events. Treatments of 100 passes were applied to each plot. The results confirmed the complex interactions that occur between topographic, soil, and geomorphic variables noted by others, and the difficulty of interpreting their impact on existing trails. None of the hypothesized relationships between water runoff and slope, soil texture, antecedent soil moisture, trail roughness, and soil resistance was statistically significant. Five independent variables or cross-products explained 42% of the variability in sediment yield when soil texture was added as a series of indicator variables. Ten variables combined to explain 70% of the variability in sediment yield when trail user was added as a second series of indicator variables. Terms incorporating soil texture (37%), slope (35%), and user treatment (35%) accounted for the largest contributions. Multiple comparisons test results showed that horses and hikers (hooves and feet) made more sediment available than wheels (motorcycles and off-road bicycles) and that this effect was most pronounced on prewetted trails. RtSUMF Impact erosif des randonneurs a pied, des chevaux, des motocyclettes et bicyclettes tous-terrains, sur les sentiers de montagne du Montana. Cette etude examine l'impact relatif des randonneurs a pied, des chevaux, des motocyclettes et bicyclettes tous-terrains, en termes de ruissellement d'eau et de production de sediments sur 108 parcelles echantillons de sentiers de montagne situees a l'int6rieur ou au voisinage de la foret nationale de Gallantin, dans l'etat du Montana. Un simulateur de pluies de Meeuwig modifie, type degouttement, a ete utilise pour reproduire des tempetes de pluie naturelles. Les traitements de 100 passes ont ete appliques a chaque parcelle. Les resultats confirment les interactions complexes entre les variables topographiques, edaphiques et geomorphiques qui avaient ete observees par d'autres chercheurs, et la difficulte d'interpreter leur impact sur les sentiers de montagne existants. Aucune des supposees relations entre le ruissellement d'eau et la pente, la texture du sol, l'humidite anterieure, l'inegalite du sentier et la resistance du sol n'est statistiquement significative. Cinq variables ind6pendantes ou produits en croix expliquent 42 pour cent de la variabilite de la production de sediments lorsque la texture du sol est ajoutee en tant que serie de variables indicatrices. Dix variables se combinent pour expliquer 70 pour cent de la variabilite de la production de sediments lorsque l'utilisateur du sentier est ajoute en tant que seconde serie de variables indicatrices. Les termes incorporant la texture du sol (37 pour cent), la pente (35 pour cent) et le traitement par l'utilisateur (35 pour cent) rendent compt...

During the last 3 decades, many road removal projects have been implemented on public and private lands in the United States to reduce erosion and other impacts from abandoned or unmaintained forest roads. Although effective in decreasing sediment production from roads, such activities have a carbon (C) cost as well as representing a carbon savings for an ecosystem. We assessed the carbon budget implications of 30 years of road decommissioning in Redwood National Park in north coastal California. Road restoration techniques, which evolved during the program, were associated with various carbon costs and savings. Treatment of 425 km of logging roads from 1979 to 2009 saved 72,000 megagrams (Mg) C through on-site soil erosion prevention, revegetation, and soil development on formerly compacted roads. Carbon sequestration will increase in time as forests and soils develop more fully on the restored sites. The carbon cost for this road decommissioning work, based on heavy equipment and vehicle fuel emissions, short-term soil loss, and clearing of vegetation, was 23,000 Mg C, resulting in a net carbon savings of 49,000 Mg C to date. Nevertheless, the degree to which soil loss is a carbon sink or source in steep mountainous watersheds needs to be further examined. The ratio of carbon costs to savings will differ by ecosystem and road removal methodology, but the procedure outlined here to assess carbon budgets on restoration sites should be transferable to other systems.

Soil carbon storage plays a key role in the global carbon cycle and is important for sustaining forest productivity. Removal of unpaved forest roads has the potential for increasing carbon storage in soils on forested terrain as treated sites revegetate and soil properties improve on the previously compacted road surfaces. We compared soil organic carbon (SOC) content at several depths on treated roads to SOC in adjacent second‐growth forests and old‐growth redwood forests in California, determined whether SOC in the upper 50 cm of soil varies with the type of road treatment, and assessed the relative importance of site‐scale and landscape‐scale variables in predicting SOC accumulation in treated road prisms and second‐growth redwood forests. Soils were sampled at 5, 20, and 50 cm depths on roads treated by two methods (decommissioning and full recontouring), and in adjacent second‐growth and old‐growth forests in north coastal California. Road treatments spanned a period of 32 years, and covered a range of geomorphic and vegetative conditions. SOC decreased with depth at all sites. Treated roads on convex sites exhibited higher SOC than on concave sites, and north aspect sites had higher SOC than south aspect sites. SOC at 5, 20, and 50 cm depths did not differ significantly between decommissioned roads (treated 18–32 years previous) and fully recontoured roads (treated 2–12 years previous). Nevertheless, stepwise multiple regression models project higher SOC developing on fully recontoured roads in the next few decades. The best predictors for SOC on treated roads and in second‐growth forest incorporated aspect, vegetation type, soil depth, lithology, distance from the ocean, years since road treatment (for the road model) and years since harvest (for the forest model). The road model explained 48% of the variation in SOC in the upper 50 cm of mineral soils and the forest model, 54%. Copyright © 2015 John Wiley & Sons, Ltd.