The Effects of Gap Disturbance on Soil Chemical and Biochemical Properties in a Mixed Beech ? Hornbeam Forest of Iran

The present study aimed to examine the impacts of small (85.12 m2), medium (325.21 m2), large (512.11 m2) and very large (723.85 m2) gaps on soil properties in a mixed beech ? hornbeam stand of northern Iran. As well as the value of pH, organic matter and carbon, total nitrogen, cation exchange capacity (CEC), phosphorus, potassium, calcium, nitrogen mineralization, microbial respiration, earthworms density and biomass of soil samples (0 ? 15, 15 ? 30 and 30 - 45 cm depths from gap center, edge and closed canopy positions) were measured in laboratory. Significantly effects of gaps size were found on soil properties as the highest values of CEC, density and biomass of earthworms observed in small gaps. The highest values of carbon to nitrogen ratio, phosphorus, potassium and calcium were detected in medium gaps. The most amounts of organic matter and carbon, nitrogen mineralization devoted in very big gaps. Greater amounts of pH, total nitrogen and microbial respiration were detected in big and very big gaps. It was found that gap position had a profound effect on soil characters as the highest values of pH, organic matter and carbon, total nitrogen, phosphorus, potassium, calcium, nitrogen mineralization, microbial respiration observed in gap center. The greatest amounts of carbon to nitrogen ratio, CEC, density and biomass of earthworms were detected in closed canopy. According to the results, soil upper layers showed the highest values organic matter and carbon, soil nutrition elements and biochemical activities, whereas the highest amounts pH, carbon to nitrogen ratio, CEC and density and biomass of earthworms were observed in deeper soil. It is concluded that opening areas of canopy cover should be less than 400 m2 in beech forests of northern Iran with considering of soil properties.