Common oak (Quercus robur L.) is one of the main forest-forming and economically most valuable broad-leaved tree species of Ukraine. Nowadays, there is a weakening of the stability of natural oak forests, which is the result of a complex of reasons, in particular the action of two powerful environmental factors – anthropogenic load and global climate changes, which lead to their degradation and mass drying. This is aggravated by the poor natural regeneration of oak trees. In the south of the country, natural oak groves have been preserved in ravine forests, which perform a number of important functions (soil protection, anti-erosion, water regulation, recreation, nature protection, a reserve of valuable vegetation, etc.). In connection with the above, forest taxation analysis and regular monitoring of the state of natural oak plantations in the steppe zone of Ukraine are important, in particular under different forest growth conditions, as they significantly affect the productivity indicators of stands.
The aim of the study was to analyse the influence of different forest growth conditions on the taxonomic characteristics and life status of Q. robur in the Yatsevo ravine of the Dnipropetrovsk region. The survey was carried out in the Yatsevo ravine of the Dnipro district of the Dnipropetrovsk region, which is a forest reserve of national importance and belongs to the southern geographical variant of the ravine forests. The subject of the research is the forestry and taxation characteristics and the life status of oak stands of natural origin of the large southern spur of the ravine (the first from its mouth). Experimental Quercus robur L. plants grew under different forest growth conditions: in a thalweg and on a slope with a north-eastern exposure. Test site 1 was in a thalweg with a flat topography (slope no more than 5°). Forest growth conditions CL2-3 (hygromesophilic). Site 2 was located in the middle part of the steep slope (27°). Forest vegetation conditions – CL1-2 (xeromesophilic). Site 3 with xerophilic (CL0-1) conditions was located in the upper part of the slope with a steep slope (23°). The area of each of the test sites was 1,800 m2.
The studied oak stands differ in the composition of associated species. The tallest Q. robur trees under all forest growth conditions belong to the height class of 14.1-16 m. Under hygromesophilic conditions, it includes the maximum number of plants (45.5%). Plants under xeromesophilic and xerophilic conditions belong to the height class 10, 1-12 m (61.8 and 63.6%, respectively). Trees up to 4 m high are found only in the CL1-2 area. Under hygromesophilic growth conditions, the largest number of Q. robur plants has a degree of trunk thickness of 64.1-68 cm, under xeromesophilic - 16.1-20, and under xerophilic - 44.1-48 cm. Analysis of the value of the average taxon indicators (height, diameter, cross-sectional area, stock) of the Q. robur stand under different forest growth conditions allowed us to construct the following ranking series: CL2-3 > CL0-1 > CL1-2. The forest stand on the CL1-2 site has worse tax indicators compared to CL0-1, despite the higher level of moisture, which is explained by the high density of associated species and undergrowth.
The vital condition index of an oak plantation under hygromesophilic conditions (CL2-3) is 86.4, under xeromesophilic (CL1-2) - 72.9, and under xerophilic (CL0-1) - 78.2. The widest range of trunk and crown pathologies is observed in thalweg conditions (8 types). On the territory of the CL0-1 hygrotop, 4 types of defectiveness were found, and on CL1-2 - 3 types.
It was established that not only the level of moisture, but also the density of the tree stand affects the tax indicators and life state of Q. robur.
