Effect of Forest Clearing and Topography on Some Soil Physicochemical Properties Effective on Soil Quality in Saravan Region, Guilan

Deforestation has detrimental effects on the environment which could result in increased flooding and soil erosion and degradation. Study on the effect of forest clearing on soil functioning within an ecosystem is evaluated by soil quality indicators, and can provide the basis to control the land degradation and develop sustainable management strategies. This research was conducted to investigate the effect of forest clearing on some of soil quality indicators in Saravan Forest Park, located in Guilan province. This region has been cleared in some parts to allow installation of the high voltage power towers. In overall, 144 soil samples were taken from 0-15 and 15-30 cm soil depths of the cleared part and its adjacent forest from four slope positions and two slope aspects. The data were analyzed to compare the effects of land use type and topography on some soil quality indicators. Some important soil quality indicators including bulk density, weighted mean diameter of aggregates, particle size distribution, pH, cation exchange capacity, organic matter content, equivalent calcium carbonate, total nitrogen, and available phosphorous and potassium were measured. The results showed that organic matter content, aggregate stability, cation exchange capacity, total nitrogen, available phosphorous and potassium of surface soils were decreased by forest clearing, whereas, bulk density, pH and equivalent calcium carbonate were increased. Forest surface soils of the hill slope with northern face had higher organic matter, total nitrogen, available phosphorous and lower bulk density compared to other parts. The results indicated that the lower slope positions had the highest amounts of organic matter, available phosphorous, and aggregate stability, and the lowest bulk density and equivalent calcium carbonate. As a result of forest clearing, average Nemero quality index (NQI) decreased by 67.7%. The results showed that the differences of soil quality indicators among different slope positions in deforested parts were more obvious than in the original forest parts. It can be concluded that deforestation may lead to surface soil degradation, which is mainly due to acceleration of soil erosion and soil transportation from top to down slope positions. Different slope positions in the forest are partly uniform due to relatively conserved soil. Considering the severity of surface soil degradation by forest clearing in power transmission lines and the considerable affected area in the region, it is essential to minimize these negative effects by conservation practices such as crop mulches, planting, terraces and diversion channels at the time of construction of these lines.