Deforestation effects on soil physical and chemical properties, Lordegan, Iran

Quantification of soil quality changes following deforestation by measurable soil attributes is important to sustainable management of soil and water conservation. A study was initiated in 1994 to evaluate the effects of deforestation on physical and chemical properties of soils under oak (Quercus brontii) forests in Lordegan region of central Zagrous mountain, Iran. Nine profiles which were derived from Bakhtiari conglomerate from three sites were selected for this research. These sites were: i) a virgin forest; ii) a completely deforested and currently utilized as crop land; and iii) a forest which has been cultivated for cropping under the trees (a type of agroforestry). Soil (coarse-silty, carbonatic, calcixerollic xerocherpts) characteristics that were analyzed include: bulk density, mean weight diameter, aggregate uniformity coefficient, organic matter nitrogen, potassium, phosphorous, pH, EC, soluble anions and cations, plasticity index, and tilth index. Deforestation and subsequently tillage practices resulted in almost a 20% increase in bulk density, 50% decrease in organic matter and total nitrogen, a 10 to 15% decrease in soluble ions comparing to the undisturbed forest soil. The filth index coefficient (average of three depths) of the forest site was significantly higher (0.717) than the cultivated forest (0.633) and the deforested (0.573) sites. Deforestation and clear cutting, of the forests in the central Zagrous mountain resulted in a lower soil quality and thus decreasing the productivity of the natural soil.