THE EFFECT OF ALTERNATIVE THINNING REGIMES ON GROWTH AND STABILITY OF SCOTS PINE PLANTATIONS IN SOUTHERN FOREST-STEPPE IN UKRAINE

The effect of selective and combination (row + selective) thinning of varying intensities on mensuration characteristics, differentiation, and productivity of middle-aged plantations of Scots pine was studied in southern Forest-Steppe in Ukraine. The experiment on thinning by combination method in planted Scots pine (Pinus sylvestris L.) stands was established in 1967 in 16-year-old pine plantations. The plantations were created in 1950 by one-year seedlings with 1.5 × 0.7 m spacing. The initial density of the stands was 9.5 thousand stems per ha. The experiment included five variants of different thinning regimes: selective thinning of moderate intensity; combination thinning with removal of every 4th row; combination thinning with removal of every 3rd row; combination thinning with removal of every 2nd row; combination thinning with removal of every 4th row at 16 years followed by combination thinning of middle rows at the age of 23. Thereafter, up to 40 years of age, the plantations were thinned twice using selective thinning from below of low and moderate intensity – 24 % by the growing stock volume. During the thinning, the plantations were kept to a specified density. 64-years-old planted Scots pine stands with a density of about 650 stems∙ha-1, in which thinning was carried out by selective method of moderate intensity and by combination (row+ select thinning) method of moderate and high intensities (with complete removal of trees in every 2nd, or 3rd, or 4th row) at the age of 17 and the subsequent selective thinning of moderate intensity, are scarcely different in mensuration characteristics. The best method was the combination thinning with the removal of each 3rd or 4th row; the method can be recommended for practice, given the high mensuration characteristics, productivity, and resistance of the thinned stands against a physical load.