The effect of litter addition on soil microbial and enzyme indices after forest harvesting operations in Hyrcanian deciduous forests, twenty years trajectory

Improvement of soil characteristics in natural conditions after ground-based forest harvesting operations is necessary to maintain soil quality. Therefore, the present study was conducted to examine the effect of different tree litters on soil microbial properties and enzyme activity of skid trails over a 20-year period after skidding operations. A total of 216 soil samples were taken from three litter treatments (B; beech, B-H; beech-hornbeam, B-H-O; mixed beech) exposed to three traffic intensity classes (low, medium, and high) that were each assigned to three time periods (6, 10 and 20 years after harvesting). All combinations were replicated three times. The highest value of soil microbial characteristics and enzyme activity belonged to B-H-O treatment followed by > B-H > B and 20-years since harvest followed by > 10 years > 6 years. Recovery of microbial properties and enzyme activities under the influence of high-quality litter (mixed beech) was positively associated with other soil properties including pH, total N, available nutrients. Values of soil microbial properties including soil microbial respiration (15%), microbial biomass carbon (8.7 %), microbial biomass nitrogen (15.4%), NH 4 + (13.6%), NO 3 - (9.8 %) and enzyme activities such as urease (10.2%), acid phosphatase (4.4%), arylsulfatase (8.8%), invertase (6.9%) in the B-H-O treatment measured 20 years after harvesting were less than the values of the undisturbed area. According to these results, it seems that the mixed beech litter treatment has been able to improve soil properties more than the other tested treatments.