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Growth and mortality of oak (Quercus robur L.) in young mixed stands with various admixture of hornbeam (Carpinus betulus L.) in the period of 9−13 years after planting were examined. The trial stand is located in central Poland (51.827023° N, 19.922315° E). It was established in 2004 on a moderately fertile site. Four experimental variants with different participation of oak (O) and hornbeam (H) were established: W1 – an oak monoculture (control variant, 100% O), W2 – a mixed stand consisting of two rows of oak and one row of hornbeam (67% O, 33% H), W3 – a mixed stand consisting of one row of oak and one row of hornbeam (50% O, 50% H), W4 – a mixed stand characterized by a single tree mixture, with three oaks and one hornbeam alternately occurring in each row (75% O, 25% H). During the first two years of the study period the height increments of oak trees were significantly larger in the study variants with hornbeam (the biggest in W3 variant), while during the next two years, the largest values of height increments occurred in the control variant (W1). Through the second part of the study period, the most pronounced, negative effect of hornbeam on the dbh increment of oak trees took place in the W3 variant. During the first nine years after planting the survival rate of oak trees in the variants with hornbeam were similar (82−94%) as in the control variant (85%). However, during the next four years, three times more oaks died in W3 variant (16,5%) than in other variants (5−7%). In general, the results obtained suggest that in order to create mixed oak stands with hornbeam as a nursery species, the share of hornbeam should not exceed 20−25% of all planted trees. The above value appears to be acceptable from the point of view of the negative competitive effects of hornbeam on oak trees during the initial stages of stand development.
We investigated annual height increment of sessile oak and common hornbeam planted on clear−cut in respect to the distance to the adjacent mature Scots pine stand. The study area was divided into 3 zones (I−III) each of 20 m width. The four analyzed treatments were defined on a basis of a mingling form: W1 – a monoculture of oak (control plot), W2 and W3 – two types of row mixture, W4 – single tree mixture. Two years after planting an annual height increment of both tree species was significantly higher in the zone I (adjacent to the mature pine stand from the SW side) than in two other zones. The same significant differences were also found at the other inventories. Although hornbeam was on average higher than oak, a growth inhibition of oak by hornbeam was not significant. The annual height increment of both species was correlated with the precipitation in June and July.
The aim of this study was to quantify 4−year growth and increment of 11− to 15−year−old, artificially regenerated hornbeam (Carpinus betulus L.) playing the role of the tending (nursery) species in the oak stand of the same age, after the silvicultural treatments aimed at reducing its competition against the oak. The study included three types of experimental treatments: decapitating of all hornbeam trees (OG), schematic reduction of hornbeam density (R50, removal of every second hornbeam in a row) and control (K, without treatment). The trial stand is located in Rogów (51.827023° N, 19.922315° E) and was established in 2004 on a moderately fertile site. The experiment was carried out in the spring 2013 (9 years after planting). Height and breast height diameter (dbh) of trees were measured every two years. During the study period, the height increment of decapitated trees was significantly larger than in R50 and K variants, while the dbh increment of trees in R50 variant was significantly larger than in K and OG variants. The height increment of hornbeam in R50 and OG variant and the dbh increment in R50 variant were positively correlated with height and diameter of trees before the treatment, while the dbh increment after decapitating was negatively correlated with tree dimensions before treatment. The decapitating treatment reduced the competitive ability of hornbeam more effectively than the schematic thinning removing 50% of hornbeam trees. After 4 years in the first case, oaks were on average 1 m higher than hornbeams, and in the second case, there was an opposite situation. In order to improve the effectiveness of the thinning treatment, a selective cutting should be performed (removal of the largest hornbeams), and in order to slowdown the regeneration of hornbeams after decapitating, the treatment should be carried out during the top of the growing season.
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