Formation of Biologically Stable Protective Pine Forests by Improvement Thinning in Northern Kazakhstan

The article deals with the effect of thinning in a permanent trial plot (PTP). The objects of care were natural clean even-aged pine forests growing in arid conditions of the Kazakh Uplands (case study of the Burabay National Park). The first thinning led by A.A. Weisman was carried out in 1994 in 25–30-year-old stands with the care intensity from 12.5 to 49.7 %. Besides the operating sections, the trial plot laid out during the research had control sections, where thinning was not carried out. The inventory indicators of the stands were determined, and the effects of thinning were analyzed in all the control and operating sections 70 years after the experiment began. The experiment proves that in dry pine forests of Northern Kazakhstan, the stock of stands in the operating sections, even 70 years after the care does not reach the volume of stock in the control sections. This also applies to the sections covered by low-intensity thinning. At the same time, thinning reduces the stock of ground flammable materials and deadwood. It increases the average diameter of trees relative to the care intensity. This enhances the fire resistance and recreational attractiveness of the plantations. An expanded distribution series of trees by natural diameter classes is observed in all sections: the number of natural diameter classes is 1.8 times greater than the normative distribution, which is one of the proofs of the specificity of the structure of the studied pine forests. The use of thinning with high intensity by the stock is the most promising. Dead standing, diseased and stunted trees are removed from the stand in the course of thinning. Thinning is recommended for 20–25 and 40–50 years old trees.