Abstract
The aim of this work was to define the features of the age structure of the silver birch stands in the Left-Bank Forest-Steppe considering forest site conditions, origin, site index and proportion of this species in the forest composition. Survival of silver birch in almost all age classes was the lowest in the relatively poor forest site conditions. The mean weighted age classes of silver birch are IV.8 in vegetative stands and IV.6 – in artificial seed stands. For all origins, the mean weighted age classes are V.1 for Sumy Region and IV.6 – for Kharkiv and Poltava Regions. The stands of the lower productivity have the least longevity. Survival of pure and almost pure stands (silver birch make 90 % of all the trees) is the lowest. At that, it is the highest in Sumy Region.
Highlights
Silver birch (Betula pendula Roth) in the forest fund of the State Agency of Forest Resources covers only 5.7% from the forest-covered area (Zahalna kharakterystyka 2016)
We studied the data for subcompartments with silver birch as the main forest-forming species according to 10-year age classes for different forest site conditions, origin, site index, and proportion of silver birch in the stand composition
We analysed silver birch stands from subcompartments with all forest site conditions, origin, site index and birch proportion in the stand and found out that in the IV age class from 30.5 % (Chuguyevo-Babchanske Forest Enterprise (FE)) to 74.3% (Skrypayivske TEFE) of the trees survived (Table 2)
Summary
Silver birch (Betula pendula Roth) in the forest fund of the State Agency of Forest Resources covers only 5.7% from the forest-covered area (Zahalna kharakterystyka 2016). Recently the health condition of silver birch has worsened in many regions (Skrylnik & Koshelyaeva 2015, Goychuk et al 2018). Our studies showed that among the trees with the diameter over 20 cm, a diameter of dead trees exceeded a diameter of living trees (Meshkova et al 2018). This indirectly indicates that the standard age of maturity and, the age of the main felling in birch stands is overstated. Due to the small proportion of the birch in the stands and its relatively early mortality, the valuable properties of this species are far from being fully utilized. We assumed that to evaluate the maturity age in unfavourable conditions for many forest species, it is necessary to take into account not their productivity dynamics only, and the risk of worsening of their health condition with age, which is accompanied by the deterioration in the quality of timber products
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