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ŠUMARSKI LIST 5-6/2020 str. 53     <-- 53 -->        PDF

growing space between the trees, the height of the trees may increase (Kerr 2003; Pinkard and Neilsen 2003; Alcorn et al. 2007; Kuehne et al. 2013) or remain unchanged (Mehari and Habte 2006; Andrzejczyk et al. 2015). As height growth plays an important role in light competition, trees tend to allocate photosynthetic production to height growth before that of diameter (Lanner 1985; Smith et al. 1997). In the present study, the tree height was greater in the two higher initial planting densities (3333 and 2500 stem ha-1), which exhibited a closed canopy (Table 3). With the higher planting density, the intraspecific competition for light may have led to increases in height growth. Furthermore, the closed canopy formed in these higher initial planting densities along with the consequent lower weed competition could have increased the height growth. According to the three-year results of this study, it was found that the weed control had increased the diameter and height growth during the period when the canopy had not yet closed (Çicek et al. 2010). Moreover, the height and diameter growth was similarly increased with weed control in common ash plantation sites (Culleton and Bulfin 1992). Kuehne et al. (2013) emphasized that tree height tended to increase with increased planting density in a 24-year-old common ash plantation which had undergone regular weed control. Because these ash species (Fraxinus excelsior and Fraxinus angustifolia) are very sensitive to weed competition, this may have been the cause of the differing results (Evans 1997; Kerr 2003; Boshier et al. 2005; Çicek et al. 2010).  Çiçek et al. (2007) stated that the weed height was found to be 1.5‒2.0 m and consequently, there was excessive weed competition in these sites. In this study, although the density and height of the weedy vegetation under the canopy could not be measured, it may be said that the density of weeds in the plots with lower planting densities (1111 and 1667 stem ha-1) was greater than in the plots with higher planting densities (Figure 1). Kerr (2003) attributed the decrease of the mean diameter with increased spacing to weed competition. 
The stem volume and aboveground biomass of individual trees were similar in all initial planting densities, as was the mean diameter (Table 3). On the contrary, it has been reported that with increased initial planting density, the stem volume of individual trees increased due to their diameter increase (Huang et al. 1999; Kerr 2003; Pinkard and Neilsen 2003). 
In initial planting density with a high number of trees, the stand levels of aboveground biomass were higher. The stocking in the widest initial planting density plot was three times that in the narrowest initial planting density plot. However, the difference in the stem volume was 3.5 times greater and the stand level of the aboveground biomass was four times greater (Table 3). Similarly, in several studies, higher aboveground biomass levels were determined in the stands with higher initial planting densities (Neilsen and Gerrand 1999; Pinkard and Neilsen 2003; Guner et al. 2010).
Tree shape – Oblik stabla
The H/D ratio is seen as an important indicator of the stem shape, especially for the bottom billet (Muhairwe 1999). An H/D ratio of 1.30 m cm-1 is critical for the stability of individual young broadleaved trees (Mosandl et al. 1991; Kuehne et al. 2013). A number of trees at the initial planting density of 3333 stem ha-1 exceeded this ratio, while trees in the other initial planting densities were below the ratio. However, as the age of the stand increases, a decrease in the H/D ratio is expected, and older trees at the planting density of 3333 stem ha-1 may fall below this H/D ratio. These results showed that the trees at planting densities of 3333 and 2500 stem ha-1 had acceptable tree stability and cylindrical stems.
The live crown ratio tended to decrease with narrower initial planting density. A similar result was also reported in an initial spacing trial of common ash (Kuehne et al. 2013). The live crown ratio in all spacing treatments was over 57%. This value was higher than the value recommended for the quality of future common ash stands, which is at least one third (Kerr 1995) or half (Kuehne et al. 2013) of the live crown height of the clear bole. Although the live crown ratio was high in the trees in the lower planting density plots, their branches could be thin, exhibit weak survival rates and provide little contribution to their crowns.
The q3.30 of trees in the initial planting density of 3333 stem ha-1 was higher than in the others, but the q5.50 and the d5.5/d3.30 ratios of the trees did not change according to initial planting density. This might indicate that the commercially important 3.30 m stem parts of the trees in the initial planting density of 3333 were more cylindrical than in the other planting densities. This supports the conclusion that tree growth in dense stands forms a more cylindrical body (Muhairwe 1994). Some studies on conifer trees have suggested that the diameter increases because after thinning or wide spacing treatments, the lower part of the stem grows relatively faster than the upper part (Muhairwe 1994; Peltola et al. 2002; Mäkinen and Isomäki 2004a; Mäkinen and Isomäki 2004b). However, the stem form may change in the following years depending on age and increasing competition.
The branch-stem dry biomass ratio, as one of the indicators of tree form, was not affected by the initial planting density. A similar result was also reported in a five years old common ash planting density experiment (Kerr 2003). This can be explained by the fact that branch mortality did not start more effectively because the closure was not fully formed.