We study the effect of roots of alder trees on soil reinforcement and slope stabilization. Two types of soil, i.e. Marl and Clayey soils and alders of three ages are considered. The slope stability is studied according to the tree indices based on tree age and soil type. The effect of root reinforcement on slope stability is considered by an additional cohesion. The stability analyses are carried out by the FEM. We perform parameter studies considering tree age, soil type and surcharge. The results indicate that soil type is effective on cohesion. The results also showed that with increasing age of trees from 7 to 15 years, the amount of additional root cohesion increased and with the increase of the age of trees to 20 years this amount slightly decreased. Also, with regard to a constant slope geometry, the type of soil and the uniform surcharge pressure, 7-year-old trees have shown better performance in slope stabilization. It has been observed that as the age of alder trees grows, although the amount of additional root cohesion increases, however, due to increased surcharge pressure, the overall slope stability factor decreases.

Farm tractor + trailers play a key role in wood transportation after forests are logged. Despite of the fact that a forwarder is a forestry vehicle that carries felled logs for shorter distances off the ground, tractors are still used in some forest areas of the world, such as the Hyrcanian forest in northern Iran. This study was conducted to investigate the possibility of using both the light forwarder and forestry trailer instead of a farm tractor + trailer in wood transportation. The optimal machine option for wood transportation is determined using goal programming model in the study area. In this paper, multi-objective goals (such as economic, operational, environmental and ergonomic) were considered. The results showed that considering only the economic goal, the contractor could save up to 44% in costs by purchasing and replacing a forestry trailer with a 2-wheel trailer attached to the farm tractor. In addition, considering various goals, a light forwarder could be selected as the optimal machine. Currently, the most important objectives of all forest contractors are to establish economic goals and reduce wood transportation costs. Since other goals, such as environmental and ergonomic, are also important; it is suggested that multi-objective approaches should use for planning.

This study proposes a method for estimation of the size and monetary value of logging damage in forest stands and on regeneration. In order to perform economic assessment of damage on regeneration and stands as a whole, each damage factor was taken into consideration and its estimated impact was converted into a coefficient. The economic damage resulting from harvesting and timber extraction was estimated with the aid of mathematical models which converted quantitative into qualitative data. In a case study from northern Iran, felling and bucking resulted in 3.2% of the regeneration being damaged, and 0.16% could have been prevented. Furthermore, with winching and skidding operations another 4.8% of regeneration was damaged, out of which 0.38% could have been prevented. The total value of preventable damage on regeneration was US $5.14 ha⁻¹ for each logging operation. The damage from felling and bucking operations amounted to 13.6% of residual trees in the stand, which was equivalent to $151 ha⁻¹ per year. Total preventable damage in various logging activities was estimated to be 15.5%, which was equivalent to $354 ha⁻¹ per year. The total value of damage resulting from logging operations was estimated to be $360 ha⁻¹.