Evaluating the Effects of Logging with a Ferguson Tractor on the Physical and Chemical Properties of the Soil. Case Study: Kouhmian Forests, Azadshahr

Forest harvesting operations, especially logging, are activities that cause interference and tampering with nature. Tractor-operated systems are the most common type of small-scale equipment used in the north of Iran. Due to the direct contact of wood with the forest soil, land logging has always been associated with a wide range of destructive effects on the forest ecosystem, including changes in the soil's physicochemical properties and damage to the natural regeneration and remaining trees. After logging, deep grooves are visible in the remaining logging roads, which can cause soil erosion, landslides, and soil fall due to the high longitudinal slope of these roads. Changes in the soil's physicochemical properties are among of the most important effects caused by the exploitation and removal of wood from the forest mass. Numerous studies report the long-term recovery of the soil's physicochemical properties. A major management goal in forest exploitation is the need to minimize the effects of vehicle traffic on the forest soil because these negative effects can be significant in the long run. The soil characteristics (appearance, compactness, and texture) and chemical properties in terms of soil elements, organic matter, and pH in two control and forest exploitation areas were studied to provide solutions to reduce these effects.

The Kohmian forestry project is located in the 89th watershed of the northern forests of Iran in the area of Natural Resources of Golestan-Gorgan province. This research was conducted in Parcel 27 of the Kohmian Azadshahr Forestry Project located in Golestan, Iran. To investigate the soil's physicochemical changes due to logging with agricultural tractors, soil was sampled in two control areas and on the crossing paths by metal cylinders at three depths (0-10, 10-20, and 20-30 cm) of the soil in a completely randomized design with three replications. These samples were dried in the laboratory in an oven at 105 °C for 24 h and then weighed using a digital scale (EK4000, Japan) with an accuracy of 0.1 g. After recording the soil dry weight, the physical properties (compaction, apparent specific gravity, moisture, and texture) and chemical properties (organic matter, cation exchange capacity, nitrogen, potassium, phosphorus, calcium, magnesium, iron, zinc, manganese, copper, and acidity) were studied using standard methods.

Logging with an agricultural tractor significantly impacted both the soil's physical and chemical properties. The most notable effect was observed in the soil depths sampled from 0-10 cm and 20-30 cm. The alterations predominantly pertained to physical changes in the soil, with no significant modifications detected in the chemical properties. Notably, soil compaction in the trafficked areas at depths of 0-10, 10-20, and 20-30 cm was respectively 46.2, 3.04, and 1.73 times higher than that of the control area. Furthermore, the increase in soil specific gravity at these depths ranged from 20% to 36% compared to the control area. Chemical properties such as cation exchange capacity and the concentrations of elements (e.g., phosphorus, nitrogen, and iron) exhibited reductions of 37.62%, 63.91%, 10.2%, and 73.05%, respectively, in the top 0-10 cm depth. At a depth of 10-20 cm, only organic matter was significantly impacted by tractor traffic, with a reduction of approximately 64% compared to the control area. Chemical properties at a depth of 20-30 cm remained unaffected by tractor traffic.

The study highlights the detrimental effects of using an agricultural tractor for primary forest plot transportation. The uneven contact surface of its tires, particularly the lower contact surface in the front tire, along with the absence of a winch, leads to soil disturbance along the logging path. This disturbance includes soil compaction, increased specific gravity, and alterations in soil texture, nitrogen, phosphorus, and iron content, reduced organic matter, and decreased soil exchange capacity. To mitigate these adverse effects, it is recommended to employ specialized logging machinery, such as skidders with rakes, instead of agricultural tractors. Other measures include implementing surface protections on logging paths, restricting logging activities to periods when the forest soil is dry and less prone to damage, and proper disposal of excess logs along the logging route.