Journal of Forestry Research (2014) 25(1): 193-200 DOI 10.1007/s11676-014-0445-2 Assessment of soil erodibility and aggregate stability for different parts of a forest road Aidin Parsakhoo  Majid Lotfalian  Ataollah Kavian Seyed Ataollah Hosseini Received: 2012-06-13; Accepted: 2012-08-02 © Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2014 Abstract: We measured erodibility and mean weight diameter (MWD) of soil aggregates in different parts of a forest road. Samples of topsoil were collected from cutslope, fillslope, road surface and forest ground to assess the texture, bulk density, moisture, CaCO 3 and organic matter. Soil aggregate stability was determined by wet sieving. Soil erodibility on the road surface was 2.3 and 1.3 times higher than on the fillslope and cutslope, respectively. The forest soil had the lowest erodibility. Aggregate stability of cutslope and road surface were low and very low, respectively. There was a significant negative relationship between cutslope erodibility with CaCO 3 and sand content. Cutslope erodibility increased with increasing silt, clay and moisture content. On fillslopes, MWD increased with in- creasing rock fragment cover, plant cover, litter cover, organic matter and sand. There was a strong negative correlation between fillslope erodibility and organic matter, sand and MWD. There was no significant difference between erodibility of bare soil and soils beneath Rubus hyrcanus L. and Philonotis marchica (Hedw.) Brid. Keywords: road prism, soil erodibility, aggregate stability, wet sieving, Lat Talar forest The online version is available at http://www.springerlink.com Aidin Parsakhoo ( ) Department of Forestry, Faculty of Forest Sciences, Gorgan Agricul- tural Sciences and Natural Resources University, Golestan Province, Gorgan, Iran. E-mail: Aidinparsakhoo@yahoo.com Majid Lotfalian  Seyed Ataollah Hosseini Associate Professors, Department of Forestry, Faculty of Natural Re- sources, Sari Agricultural Sciences and Natural Resources University, Sari, Iran. Ataollah Kavian Assistant Professor, Department of Watershed Management, Faculty of Natural Resources, Sari Agricultural Sciences and Natural Resources University, Sari, Iran. Corresponding editor: Yu Lei Introduction Mountain roads are the most prodigious source of sediment be- cause of low stability of road aggregates and high erodibility in some part of its prisms (Sidle et al. 2011). Aggregate stability of a soil is the resistance of soil structure against mechanical or physical-chemical destructive forces. Determining aggregate stability will give information on the sensitivity of soils to water and wind erosion, which might be prevented by revegetation (Mandy et al. 2009). Revegetation of the road cutslopes and fill- slopes increases soil aggregate stability by accelerating vegetation development and by promoting soil formation processes such as accumulation of fine soil particles, organic matter and mycorrhizal propagules (Burri et al. 2009). Aggregates can form by the breakdown of consolidated soil mass into smaller sizes (Dvorak and Novak 1994). Soil aggregate stability and size distribution vary widely over time and space (Kusky 2008). Aggregate density affects soil erodibility to a lesser extent but is much less variable than stability and size distribution (Morgan 2005). Soil erodibility factors quantify the susceptibility of soil detachment by water. These erodibility factors predict the long-term average soil loss (Bryan 2000; Mbagwu 2003). Road prisms including cutslopes, road surfaces and fillslopes can be important contributors of sediment to streams in forested watersheds. The road surface is the compacted area used to sup- port traffic. The cutslope is created by excavation into the natural hillslope, and it is steeper than the natural slope. The lack of aggregate stability directly affects surface erosion rates in un- protected soils of cutslopes (Clayton 1983). Fillslope is an un- consolidated excavated material pushed to the slope below the road; it is also steeper than the natural slope (Jordán-López et al. 2009). Previous works suggested that cutslopes are a significant source of sediment and possibly the primary sites of erosion as a result of logging operations (Megahan 1978; Riley 1988). Jordán and Martínez-Zavala (2008) reported that the soil loss from the ORIGINAL PAPER