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Although the effects of different vegetation cover on soil reinforcement due to their roots have been addressed in the literature, there remains a lack of assessment and comparison of root biomechanical properties of hardwood and softwood plantations for similar site conditions. To address this gap, two adjacent hillslopes with similar site conditions but different forest plantations, a Picea abies (softwood) and a Fraxinus excelsior (hardwood), were selected to assess and compare their effectiveness in protecting sloping soils. The profile trench method was used to obtain root distribution from both upslope and downslope sides of tree samples and on each side at two horizontal distances from the tree stems. Root tensile strength of live root samples was measured using a standard Instron Universal Testing Machine. A modified Wu and Waldron root reinforcement model was used to calculate root cohesion for the two plantations. The root tensile strength for was significantly greater for softwood than for hardwood trees (19.31 [+ or -] 2.64 vs 16.98 [+ or -] 1.01 MPa). Interestingly, the number of roots, root area ratio values, and the root tensile strength of the two species did not significantly differ between the upslope and downslope sides of trees. The results also showed a higher root cohesion for the softwood than the hardwood species (1.56 [+ or -] 0.34 vs 1.03 [+ or -] 0.21 kPa). In addition, softwood trees extended their contribution to soil protection to a larger horizontal distance compared with hardwood. However, our findings generally revealed that the values of root cohesion of both studied plantations were surprisingly lower than those found in earlier reports. Keywords: plant roots, soil bio-engineering, soil cohesion, soil protection, slope stability., Introduction Landslides are major environmental hazards (Morgan and Rickson 2005; Veylon et al. 2015). Although they are a result of natural geomorphological processes, they are both affected by and have [...]

Abstract: An experimental campaign was set up to quantify the contribution of evapotranspiration fluxes on hillslope hydrology and stability for different forest vegetation cover types. Three adjacent hillslopes, respectively, covered by hardwood, softwood, and grass were instrumented with nine access tubes each to monitor soil water dynamics at the three depths of 30, 60, and 100 cm, using a PR2/6 profile probe (Delta‐T Devices Ltd) for about 6 months including wet periods. Soil was drier under softwood and wetter under grass at all the three depths during most of the monitoring period. Matric suction derived via the soil moisture measurements was more responsive to changes in the atmospheric conditions and also recovered faster at the 30 cm depth. Results showed no significant differences between mean matric suction under hardwood (101.6 kPa) with that under either softwood or grass cover. However, a significant difference was found between mean matric suction under softwood (137.5 kPa) and grass (84.3 kPa). Results revealed that, during the wettest period, the hydrological effects from all three vegetation covers were substantial at the 30 cm depth, whereas the contribution from grass cover at 60 cm (2.0 kPa) and 100 cm (1.1 kPa) depths and from hardwood trees at 100 cm depth (1.2 kPa) was negligible. It is surmised that potential instability would have occurred at these larger depths along hillslopes where shallow hillslope failures are most likely to occur in the region. The hydrological effects from softwood trees, 8.1 and 3.9 kPa, were significant as the corresponding factor of safety values showed stable conditions at both depths of 60 and 100 cm, respectively. Therefore, the considerable hydrological reinforcing effects from softwood trees to the 100 cm depth suggest that a hillslope stability analysis would show that hillslopes with softwood trees will be stable even during the wet season. [ABSTRACT FROM AUTHOR]

Forest roads are important for adequate management of natural resources, but they are also a dominant contributor of sediment to forest streams and water pollution. This study measured road sediment concentration from forest roads to determine the impact of rainfall intensity and cutslope types on sediment concentration in the Patom district of northern Iran. Two 110 m road segments with variable soil and rock fragment cover exposed at the cutslopes were studied. Seven rainfall and corresponding runoff events were measured in 1-liter bottle samplers every 10 minutes at the outlet of cross sectional culverts, and from two 3 m² plots on the roadbeds adjacent to each cutslope. A statistically significant difference at the 95% confidence level between two cutslope types and rainfall intensity on sediment concentration was determined from the field data based on nonparametric tests, though no statistically significant difference in the concentration of sediment between the two roadbeds plots were found. The average of sediment concentration of soil trench and the rock fragment cover cutslopes were 60.3 and 46.8 g/l, respectively. The results reported here should help forest road managements to improve the understanding of cutslopes erosion and sediment production from forest roads and to employ suitable methods to reduce sediment production. [ABSTRACT FROM AUTHOR]

Forest roads are important for adequate management of natural resources, but they are also a dominant contributor of sediment to forest streams and water pollution. This study measured road sediment concentration from forest roads to determine the impact of rainfall intensity and cutslope types on sediment concentration in the Patom district of northern Iran. Two 110 m road segments with variable soil and rock fragment cover exposed at the cutslopes were studied. Seven rainfall and corresponding runoff events were measured in 1-liter bottle samplers every 10 minutes at the outlet of cross sectional culverts, and from two 3 m² plots on the roadbeds adjacent to each cutslope. A statistically significant difference at the 95% confidence level between two cutslope types and rainfall intensity on sediment concentration was determined from the field data based on nonparametric tests, though no statistically significant difference in the concentration of sediment between the two roadbeds plots were found. The average of sediment concentration of soil trench and the rock fragment cover cutslopes were 60.3 and 46.8 g/l, respectively. The results reported here should help forest road managements to improve the understanding of cutslopes erosion and sediment production from forest roads and to employ suitable methods to reduce sediment production. [ABSTRACT FROM AUTHOR]

An efficient and low-cost transportation network is necessary for sustainable management. Roading and log skidding are the most expensive and destructive operations in forest environment, unless carefully planned and evaluated. A transportation network has to be assessed and optimized to minimize the total cost of road construction and its environmental impact. The aim of this study was determining the optimum forest road network density, and evaluating the quantity and quality of the existing forest road network. In order to determine the optimum forest road network density, skidding cost, road construction and maintenance costs, and harvesting volume in each compartment were considered. Then optimum skidding distance was calculated with regard to optimum road density and total correction factors. The relative openness and efficiency coefficient of the existing forest road network were determined for the calculated optimum skidding distance, using ArcGIS. The results showed that the optimum road density, relative openness and road network efficiency coefficient were 21.5 m ha-1, 90% and 32%, respectively. As a result, when the quality of a forest road network has to be evaluated, road network efficiency coefficient is more efficient than relative openness, that per se cannot be considered as an appropriate indicator. [ABSTRACT FROM AUTHOR]