Quantitative characteristics, regeneration status, Physicochemical soil properties within and at different distance of abandoned skid trails in the Hyrcanian forests.

Abstract

Background Creating skid trails for wood extraction in mechanized harvesting is unavoidable. Creating such a trial is a temporary changes in forest condition that causes significant influences on the disturbed area. The area gradually turns to the forest that depends on several edaphic and climatic factors. The process from bared land in the skid trails to the forest area need to be investigated in order to know the time and process of changes. It is also interesting to know the stand condition around the skid trail due to harvesting. The objective of the study was to investigate the stand characteristics within the abounded skid trails and as well as within the stand. Methods In this study, three 35-year-old abounded skid trails were selected and 63 rectangular plots with the dimensions of 200 m x 5 m for stand characteristics and 100 m2 (20 m × 5 m) for regeneration were established within and at intervals of 25, 50 and more than 75 m on both sides of the skid trails. Soil sample were also taken at center of each plot. Stand characteristics such as species, d.b.h, height, and crown diameter were measured. A factorial test was used to examine the relationship between various distances of trails and position of samples and independent variables such as d.b.h. Results The average d.b.h was 27.3 cm, 35.9 cm, 30.9 cm, 25.8 cm, 35.1 cm, 32.6 cm, and 16.4 cm at 25+, 50+, 75+, 25-, 50-, 75-, and within the trails, respectively. Along the skid trails, the main trees were alder and around the skid trails, the dominant trees were beech. Available P level was high within the trails. The regeneration status was relatively favorable within the trails and at different intervals of skid trails. Discussion In the study of stand composition, beech trees had the highest percentage at all intervals of the skid trails, and maple and alder trees were rarely found; however inside the trails the alder trees were dominant. Creating skid trails is an interference within an ecosystem which may lead to the creation of side effects due to harvesting and soil disturbance. Along the skid trails, where the canopy is opened-up, and the soil is disturbed, alder trees are established. The abundance of beech trees in the area was due to the altitude and climatic conditions which is suitable for establishment of beech stands. Results for frequency of regeneration less than 1.30 m in height indicate that with increasing distance from the skid trails, the rate of regeneration decreased. Getting enough light to the forest floor inside the trails by opening the canopy, provides a suitable condition for regeneration, especially for pioneer species. Regeneration of alder trees in the skid trails was higher than outside of the skid trails, which has a direct relationship with the displacement of soils and increased light as a pioneer species. Conclusion Abandoned skid trail provides suitable opportunity to study dynamic of forest stand in the bared area due to harvesting operations. As it was expected; pioneer species like alder trees occupied abandoned lands. Beech trees as a climax trees take places at the last stage of natural succession. Management and silvicultural treatment should focus on reducing unwanted species and enrichment abandoned skid trail by other species. Further study can be done after 15 years to see what happened after half century.