Understanding the effects of silvicultural practices including single-tree selection on soil properties is essential for forest management in temperate broadleaved beech forests. Changes in physico-chemical and biological soil properties in 15 harvest-created gaps under single-tree selection and the adjacent closed canopies, with five replications for each, were studied 6 years after gap creation in an oriental beech (Fagus orientalis L.) stand of the Hyrcanian forest. Gaps were classified into three size classes: small (85-130 m 2 ), medium (131-175 m 2 ) and large (176-300 m 2 ). Soil cores were collected at the center and at the edge of gaps, and under the adjacent closed canopy. Results indicated that gap size significantly affected soil texture and bulk density, whereas soil organic carbon (SOC), total nitrogen and pH showed a significant gradient from the center to the edge of gap independently form their size. SOC and total nitrogen at the center of gaps were also significantly lower than closed-canopy, in particular for the medium-gap; contrastingly, the bulk density with the highest mean value was found at the center of the large-gap. Gap size had no significant influence on soil microbial biomass. These results highlighted that similar conditions in terms of many soil properties were still present among gaps and adjacent closed-canopy stands six years after logging, though canopy openness triggered a reduction in carbon and nitrogen availability along with the related microbial activity at the center of gaps, independently from their size. Therefore, if aimed at preserving an uneven aged structure along with soil quality in temperate broadleaved deciduous forest as the oriental beech stands in the Hyrcanian region, single-tree selection practice for harvesting trees can be recommended as sustainable forest management type.Citation: Amolikondori A, Abrari Vajari K, Feizian M, Di Iorio A (2020). Influences of forest gaps on soil physico-chemical and biological properties in an oriental beech (Fagus orientalis L.) stand of Hyrcanian forest, north of Iran.

Background In the Hyrcanian temperate forests, different canopy gaps sizes have been created by logging under silvicultural methods. Understanding the effects of gaps on forest ecosystems can help in the planning and decision‐making of forestry practices. Variations in ecological conditions caused by canopy gaps may have an impact on the forest stand, particularly soil nutrients. Aims The purpose of the present research was to investigate the changes in soil organic carbon (SOC), total nitrogen (N) and phosphorus (P) stocks under different gap sizes in the Hyrcanian oriental beech forest. Methods We measured SOC, N and P stocks of soil at the depth of 0–20 cm among 15 artificial gaps along with adjacent closed stand which was created by single‐tree selection system in oriental beech stand, northern Iran. In the center and four cardinal positions of the edge of gaps as well as in the four adjacent closed canopy forests at the distance of 20 m from gaps, the soil sampling was performed. Results The difference in C, N and P stocks among the artificial canopy gaps was statistically significant, and higher mean values were observed in large gaps. No significant difference was observed between gaps and adjacent closed stands with regard to soil C, N and P stocks. At artificial gaps and closed stands, the SOC stock was negatively correlated with clay and positively correlated with bulk density, sand, N and OC. With increasing bulk density, sand, N, P, and OC, N stock was increased in gaps. In gaps, SOC and P stocks were both positively related to soil microbial C and soil microbial P, respectively. Conclusion Generally, it can be stated that there are similar relative ecological conditions between artificial gaps and closed stands, and the interaction among soil properties in gaps demonstrates gap dynamics in deciduous, broad‐leaved beech forest.

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