The results of studies of natural regeneration development in unclosed oak crops of the Northern Steppe of Ukraine allow us to conclude that the largest total amount of natural regeneration was observed in 8-year-old crops – 58.19 thousand pieces-ha-1. In seven-year-old crops, this figure was slightly lower and amounted to 40.26 thousand units ha-1. In six- and nine-year-old crops, the total amount of natural regeneration was approximately the same – 24.1 thousand units ha-1 and 24.19 thousand units ha-1, respectively. When distributing the undergrowth by height groups, the following gradations were established: within the height range of 0-0.25 m, 10.6-15.1 thousand pcs. -ha-1 (49%) of the undergrowth; within 0.26-0.50 m – 4.4-11.6 thousand units ha-1 (27%); within 0.51-1.00 m – 0.4-7.6 thousand units ha-1 (19%); within 1.01-1.50 m – 0-4.8 thousand units ha-1 (8%) of the undergrowth. The species composition of shrubs on fresh logs is similar to the parent plantation, dominated by shade-tolerant species such as Tatar maple, black elderberry, warty and European cowberry. Their distribution on the area is uneven, with a height of 0.4-0.6 m, an occurrence of 40-50%, and a closeness of 0.2-0.5. With the increasing age of the log house, in addition to shade-tolerant species, bush and forest edges appear – dogwoods, common hawthorn, wayfarer, harsh downy-rose, blackthorn, hazel. Their density is 3.1-8.9 thousand plants ha-1 with a shrub canopy closure of 0.6-1.0. The study of the root-bearing soil layer revealed that the bulk of both large and small roots in 40-year-old oak and ash crops are concentrated in the upper 0-80 cm soil layer. The maximum number of large roots – 62.8% – is located in the 20-40 cm layer. Deeper than 80 cm, their number does not exceed 5%, gradually decreasing with depth. The maximum number of physiologically active small roots of petiolate oak and common ash is concentrated in the uppermost, 0-20 cm layer – 22.5 % of the total mass. In general, the number of small roots of the petiolate oak and common ash to the total mass of the entire root system is only 7.5 %.
When assessing agrotechnical methods of creating and growing oak crops, it was found that the row spacing has a significant impact on crop productivity – with its reduction, oak trees grow taller. The stock of oak at 2-metre row spacing is 212-269, at 3-metre - 321, at 6-metre – 198-270 m3-ha-1. There is a dependence of the average oak growth on the row spacing: at 2 m it was 3.6 m3-ha-1, at 3 m - 4.4 m3-ha-1 and at 6 m - 2.7 m3-ha-1. The analysis of the assortment structure of 80-89-year-old crops revealed that with a row spacing of 4 m, the largest percentage (41 %) of oak business trees is in the 32-36 cm thickness stage. In oak-acacia cultures at the age of 28 years, the height of oak is 13.7 m, acacia - 15.2 m, diameter of oak - 9.6 m, acacia – 12.3 m. This indicates faster growth of acacia, but this species begins to dry out. By the age of 49, the acacia completely falls out of the plantation. Due to the selection of acacia rows, the plantation's fullness is reduced to 0.56-0.72, and the total stock is 162-184 m3-ha-1. Thus, the use of the forestry potential of oak forests is reduced to 60-70%. Continuous oak and linden cultures at the age of 32 and 74 years grow according to the Ib bonita, have a fullness of 0.91-1.03 and an average growth of 5.3-5.4 m3-ha-1. Heart-leaved linden forms a highly productive first tier along with oak. Oak plantations aged 57-63 years, created by the tree-shrub mixing method, have a stock in the range of 299-302 m3-ha-1, and an increase of 6.0-6.9 m3-ha-1. Compared to pure oak stands, their height is 6 % higher, their diameter 11 % higher, their stock 15 % higher and their growth 12 % higher. In oak-maple crops created by mixing pure rows, maple trees have a higher height and average diameter than oak trees and occupy a dominant position in the upper tier of mixed stands. Oak and ash crops aged 85-89 years have a stock of 439-503 m3-ha-1 and a growth rate of 4.5-5.7 m3-ha-1. The average height of oak is 27.1-29.1 m, ash 28.1-29.3 m. With an ash content of 30 %, the two main species compete with each other, and with an ash content of more than 50 %, oak is displaced from the upper tier. The method of establishment of oak crops has an impact on their average height. Cultures created by sowing in II-VII age classes have 10-15% higher height compared to planted cultures. There was no significant statistical difference in diameters. The stock of oak plantations depends on the method of creating crops. The average oak stock on the 45 surveyed test plots aged 10-64 years was 171.5 m3-ha-1 for sowing and 118.3 m3-ha-1 for planting, which is 32 % less.
Keywords: stands of dry and fresh oak forests, agrochemical properties of the soil layer, natural regeneration, productivity, row spacing, mixing schemes.
