soil changes induced by hardwood and coniferous tree plantations establishment: comparison with natural forest soil at berenjestanak lowland forest in north of iran

increasing urbanisation and industrialisation have led to a dramatic reduction in forest area, and now only culturally protected remnants of natural forests and some new plantations remain in most areas of the north of iran. to investigate the status of the chemical and physical characteristics of soil under these remnant forests and assess the possible impacts of reforestation on soil properties in the plantation forests, soils at 0-10, 10–20, and 20–30 cm depths were sampled from four tree plantations 22 years of age and it covers 42ha, composed of pinus brutia l., populus nigra l., acer velutinum boiss and fraaxinus excelsior l. species, which is located in the south of town of ghaemshahr in berenjestanak lowland forest in the north of iran, where there was remnant natural forest, and soil phkcl and phh2o, total nitrogen, soil organic matter (som) and soil organic carbon (soc) contents, exchangeable cations (ca, mg and k) contents and saturation moisture were determined. results showed that the amount of som of the first layer of the soil profiles in all forest types was greater than the other two layers. furthermore, soil ph was significantly lower in pinus brutia l. plantation than the other forest types at 0-10 cm of soil depth. a positive value for ∆ph demonstrate the presence of negatively charged clay colloids and the cation exchange capacity is higher than the anion exchange capacity .soil exchangeable k and ca contents were significantly lower under plantation forests than under natural forest in all layers, whereas exchangeable mg contents showed little difference between types of forests.  moreover, contents of all exchangeable cations except mg showed a significant decrease with depth. the value of soil moisture in the topsoil was higher than in the subsoil in all the categories of the natural forests and the tree plantation studied. the comparison indicated that the tree plantation conducted in this region must be forwarded to mixed forest under tending operations instead of monoculture to enhance and improve soil physicochemical statues.