Variability analysis of aggregate stability and soil organic matter fractions in pure forest stands

After 28 years, the effects of Alnus subcordata (AS), Acer insigne (AI), Cupressus sempervirens (CS) plantations and also bare land on soil aggregate stability and particulate organic matter (POM) were studied in Darabkola forest located in Sari, Iran. In each stand, six soil profiles were sampled at depths of 0-10 and 10-20, resulting in 12 soil samples for each stand. The samples were transferred to laboratory for analysis. The soil properties were analyzed by using two-way analysis (ANOVA) procedure, treating forest stands and soil depths as factors with interaction. Results are indicating that the variability of soil physico-chemical and biological properties, i.e., bulk density, texture, moisture, pH, EC, lime, carbon (C), nitrogen (N), available nutrient, earthworms density/biomass, in different studied areas. According to our data, the plantation increased aggregate stability, POM-C and POM-N in both of depths. The upper and lower layers of soil had the highest amounts of soil aggregate stability (79.3 and 82.4 %), POM-C (4.24 and 3.56 g/kg) and POM-N (0.45 and 0.4 g/kg) under the AS forest stand. The least values of these characters were found under bare lands (50.54 and 52.76 %, 1.98 and 1.48 g/kg, 0.22 and 0.16 g/kg, respectively). Results showed that the planting of AS trees improved aggregate stability and POM and it is recommended for rehabilitation of degraded forest areas.