Influence of silver birch (Betula pendula L.) admixture on growth and shape of pedunculate oak (Quercus robur L.) in plantations in Krynki Forest District
Influence of silver birch on 10–11 years old pedunculate oak growth and shape depends on the form of species mixture. Greater differences of height, d.b.h., branches thickness and height/d.b.h. ratio appeared between two variants with artificially introduced birch in form of rows (variant I – 3 rows of oak and 1 row of birch; variant II – 2 rows of oak and 1 row of birch) than between each of that variants and the control (with admixture of birch in the form of natural regeneration). Oaks from variant I had significantly bigger height and d.b.h., as well as their increments in comparison to variant II. Oak from the variant III (control) had intermediate values of these parameters.
From the variant I it was found that the influence of birch on growth and shape of oak depends on the distance between two species. Oak growing in rows just next to birch (distance 1.5 m) was significantly smaller, of lower d.b.h. and diameter of branches and greater slenderness than oak growing in the middle row (3 m apart of birch). The growth of oaks in the middle row was stimulated by birch. In the case of this form of mixture birch might be kept in the stand during the phase of thicket and later it should be gradually replaced by shade tolerant species (beech, hornbeam, lime), that will form a lower layer in the oak stand.
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