English oak (Quercus robur L.) is one of the most stable and durable wood species in the northern steppe. The resistance of oak depends not only on site conditions but also on the structure of the stands. The simplified structure causes weakening and further deterioration of health condition of the stands. In forming the stands more attention has to be paid to the shape and the form of future plantings. The aim of the work is to analyze the structure of artificial oak stands of the Velikoanadolsky forest area to optimize their formation.
Materials and Methods
The establishment of plots and collection and processing of field data were carried out in accordance with generally accepted forestry and forest mensuration methods. Features of growth and structure of the oak stands were studied using Field-Map technology. Accounting for natural regeneration was performed by the method of URIFFM.
Hard climatic conditions of southwest of Donetsk region, the lack of natural forests necessitated artificial afforestation of this area. The share of “Velikoanadolsky Forest Economy” accounts for 10 % of the total area of oak forest Donetsk region. Forest resource of the Velikoanadolsky forest area is also presented mostly by oak plantations, the bulk of which (84 %) are growing in fresh elm-maple fertile oak forest conditions. The share of artificial plantations is 86 %; they grow mainly by II site class, and their average age is about 85 years. The health condition of pure oak plantations (the share of their area is above 28 %) is significantly worsened with aging. Oak stands of the Velikoanadolsky forest area have a simplified structure.
Previous natural regeneration is missing, poor or inadequate for the most of the oak stands of the Velikoanadolsky forest area (74 % of the area). 25 % of the oak forests have a sufficient natural regeneration of economically valuable species of mostly 2-3-year-old advance growth. A success category of the natural regeneration in these sites is «satisfying» or «good». The composition of natural regeneration under the canopy of oak stands is mostly mixed, but the young growth of the main species, oak, is almost missing. The advance growth of maples and common ash is dominating.
The features of horizontal structure (the degree and the nature of crown closure and type of tree spacing on the site) are important to characterize structure of stands. The results indicate that in the Velikoanadolsky forest area, the majority of trees (90%) are of the 1st category (trees having freely spaced crowns which are separated from the crowns of neighboring trees and only partially are in contact with branches of neighboring trees). This biological feature of oak to be considered within forestry activities aimed at forming the structure of the stands.
The relationship between the feeding area of oak trees and the crown projection area was established. The crown projection area grows in proportion to the increase of the oak feeding area. The crown projection area ratio to the feeding area can be used for setting the limit values of feeding area for the growth and development of trees, including the establishment of acceptable variation of stand density. The calculations show that the oak density in the 1st layer of modal artificial oak stands aged 91–100 year should be at least 150–160 trees per 1 hectare.
The advance growth is often associated to the open canopy, to the sites with adequate lighting and moisture and without dense soil cover. The optimal stand density of a parent stand is 0.50–0.70, where the maximum amount of the advance growth (15–17 thousand pcs. per 1 hectare) is observed. The combined principal felling plus thinning, aimed at regeneration of oak stands using advance growth, can be implemented in the forests of Velikoanadolsky forest area.
The oak stands of Velikoanadolsky forest area have simple vertical and horizontal structure. Based on the characteristics of the structure and the health condition of oak stands, it is necessary to form mixed and complex stands. The advance regeneration of artificial oak stands is represented mainly by advance growth of economically valuable species, Norway maple and common ash. The share of oak advance growth is not large. This should be considered when dcheming combined principal felling plus thinning in oak stands of Velikoanadolsky forest area.