Effects of thinning on seedling growth and soil nutrient status in stand initiation stage of eastern beech

The gap between the demand for and supply of wood progressively widens at the expense of supply. Increasing demand for other uses including water, wildlife, recreation, etc. from forests causes further reduction of the forest area from which wood is produced. Therefore, in order to acquire greater production from progressively decreasing total forested area and increase the versatility of the areas for other uses, new approaches are needed to increase the unit productivity of the areas. This study aims to assess the effects of pre-commercial thinnings carried out at different intensity on the growth and nutrition of seedlings growing on natural regeneration sites of beech, which is a significant forest tree species for wood production.The experiment was carried out on three beech natural regeneration sites (blocks) situated at different altitudes in the Deredibi Forest Chiefship of the Düzce-Akçakoca Region. The sites had been site-prepared using bulldozers and had four-year old beech seedling at the beginning of the experiment. Five 20 x 20 m experimental units were installed for each block. Pre-commercial thinnings at various intensities were carried out, leaving one (M1F), two (M2F), four (M4F), and eight (M8F) seedlings per m2 for the first, second, third, and fourth experimental unit, respectively. A control unit where no treatment was carried out was also installed for each block, in addition to the thinning treatments.The initial root-collar diameter, height, biomass, nutrient content, and projected leaf area (LA) of beech seedlings growing on the experimental sites were measured using destructively sampled seedlings. The same seedling variables were re-measured two years after treatment, using 30 randomly selected, destructively sampled seedlings. In addition, the OM of the experimental units was sampled to the mineral soil for biomass and nutrient analyses.For soil analyses, after soil OM was sampled from five randomly selected locations on each unit, two sets of soil samples were collected from 0-10 and 10-20 cm depths using a core sampler. One set of the soil samples was used for bulk density calculations whereas the other sample set was utilized for texture, pH, cation exchange capacity, and nutrient content analyses.Moreover, resin bags were placed in five 25-cm deep soil pits that had been randomly selected for each experimental unit in order to determine the effects of the treatments on the amount of nutrients leaching out of the soil profile. Depending on precipitation, the bags were renewed for every 1-1.5 month, which were later analyzed using ion chromatography.Following analyses, the seedlings of the control treatment had the greatest height and the second greatest diameter growth. The lowest seedling height and diameter growth was found on the unit with the lowest seedling density (M1F).The greater LA of the M1F seedlings when compared to those of the M8F and M4F seedlings indicated that the former seedlings had been subject to shade more. The M2F seedlings averaged a greater N concentration than did the seedlings of the other treatments. P content was greater for the M8F seedlings when compared to the seedlings of the other treatments.In conclusion, the data suggested that it was early to make interpretations and recommendations for the practitioner at this seedling age for the proper intensity of pre-commercial thinning in terms of seedling growth and nutrition as well as soil nutrient content.