Species composition of birch stands of the Eastern Polissya of Ukraine is formed by two dominant tree species: silver birch (Betula pendula Roth.) and downy birch (Betula pubescens Ehrh.). Both birch species are heliophilous, moderately soil-demanding and frost-resistant. Therefore, they are considered in conjunction, for the creation and formation of birch forests. Under plentiful seed production and frequent repetition of seed years, the birch stands form pioneer groups on non-forest lands. On cuttings and burnt forest areas, birch trees form the secondary forests. Artificial birch stands are often created on the plots after clear sanitation felling of irregular pine stands to improve the soil properties and form productive resistant forests. The secondary stands are usually inferior in productivity, merchantability and biological resistance as compared to virgin forests.
Materials and Methods
Research carried out during 2004–2016 in the forests of state forest enterprises of Eastern Polissya. 29 permanent sample plots were laid out in birch stands. On the sample plots, the origin of stands – natural or artificial (forest culture) – was determined. Birch stands of natural origin were divided into seed and vegetative (coppice) ones. During investigations of trees on the sample plots, the diameters at a breast height were measured as well as Kraft class and category of health condition was identified (using classification of “Sanitary regulations in forests of Ukraine”, 1995). The actual productivity of birch stands was compared with tabular data from the normative documentation.
Results and Conclusions
As of 01.01.2012, birch stands covered an area of 45.46 thousand ha (10.4 % of lands covered with forest vegetation) in the forests of the state forest enterprises of Eastern Polisya. The growing stock of birch forests was 8,144.5 thousand m3 of wood.
By the age structure, middle-aged birch stands are dominated (52.7 % of the area). A large proportion of mature and overmature birch stands (24.7%) indicates a reduction of felling in the birch working circle.
The largest area of birch stands belongs to the fresh and moist fairly infertile pine site types (25.5 and 23.4 %, respectively), as well as to the moist and fresh fairly fertile site types (22.4 and 12.6 %, respectively).Average inventory indexes of birch stands in Eastern Polissya are as follows: age – 44 years, stand density – 0.76, site class – I,4, growing stock – 179.1 m3?ha-1.Birch stands of vegetative origin predominate (54.3 %). Area of artificial birch stands is 14.18 thousand ha or 31.2 %. Most of the birch forests of natural origin have mixed composition and therefore are more resistant against extreme biotic and abiotic factors.Artificial birch plantations created in the areas after clear sanitation felling of pine forests infected by root rot (Heterobasidion annosum (Fr.) Bref.) have worsened health conditions and low productivity.Up to 20 years of age, the growing stock of modal birch stands is almost identical with that of fully stocked (normative) birch stands of seed origin. With increasing age, the actual productivity of birch forests comes to rank below the tabular data. Growing stock of birch forests of middle and older age is lower that of fully stocked birch stands of I–Ia site classes by 20 %. The health condition of the birch stands is deteriorating with increasing age and decreasing the share of birch in the composition.The actual yield of merchantable birch wood in mature and overmature stands is 83–94 % of the growing stock. The share of commercial wood is 22–53 %, which corresponds to the 2nd and 3rd merchantability classes.