The effect of harvesting intensity in the single tree selection system on mixed Hornbeam stand characteristics

Tree marking and harvesting intensities in the single-tree selection method are a function of the stand characteristics, site description, and expert opinion in silvicultural practices. The different harvesting intensity has a significant effect on the remaining stands and the regeneration characteristics that introduce the forest’s future st. The impact of harvesting intensity on forest characteristics and forest stands specific to Hyrcanian forest structure has not been evaluated. This study investigated the silvicultural characteristics of mixed Hornbeam stands in control and compared them with different harvesting intensity stands.

A regular randomized sampling layout with a 300 × 400 m dimension was used in this research. The trees and shrubs characteristics of 70 sample plots of half a hectare were collected in harvested and control stand in 24 parcels. Forest stands were classified into three harvesting intensity groups low, medium, and high and without harvesting (control) based on the harvesting council report. The stand structure determines by using the triangle structure of the French Forestry Society. According to the total number of trees in 5 cm diameter classes and semi-logarithmic Y axis, 40 and 90 cm diameter classes were determined as the limit of small, medium, and large diameter classes.

The Hornbeam density as the main species in the harvested stands was higher than that of the control stand, but it had a smaller diameter at the breast height. The results showed that harvesting intensity had no effect on the characteristics of Lorey’s height, trees volume, and the volume of deadwood, while its effect on the diameter at the breast height and the trees crown characteristics, especially the height of the trunk and crown, the trees canopy surface area and volume was significant. The lowest harvesting intensity had the greatest additive effect on the tree crown (47%) and tree canopy volume (142%) and increasing in the harvest intensity recovered in the trade stem volume characteristic in the short time. The harvested stand structure did not significantly change with the control while the highest harvesting intensity made it younger and created a small and medium diameter class. The medium harvesting intensity was the most similar with control stand structure in terms of the placement of the samples in the seven structural classes. Most of the stands had an irregular structure, and large and intermediate-large diameter class, which is indicative of the uneven age and irregular structural condition of all mixed hornbeam stands.

The results showed that harvesting intensity less than 13.5% was improved the stands characteristics in mixed Hornbeam stands which indicating the importance of forest management and the impact of implementation of the single tree selection method in maintaining and improvement in forest stand structure. The stand structure in medium harvest intensity (between 3.5 and 9.5 percent) is closed to the control stand, so this harvesting intensity is introduced as the optimal intensity in accommodating the structure of the mixed Hornbeam stand of the eastern Hyrcanian forests located in the intermediate altitude from sea level.