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ŠUMARSKI LIST 5-6/2020 str. 54     <-- 54 -->        PDF

Branch characteristics – Karakteristike grana
The natural pruning ability of common ash is very high compared to other broadleaved species such as beech and oak (Hein and Spiecker 2009). This high self-pruning ability is attributed to the high light demand of the ash leaves. Its low resistance to branch rot may also play an important role in natural pruning. As with the common ash (Kerr 1995), at the end of the narrow-leaved ash  rotation period, a clear bole diameter of  40‒60 cm and a height of at least 6.0 m is desired. Initial spacing can affect the height of the lowest branch (height of clear bole), branch thickness and length. The size of the branches is largely controlled by the space they have in which to develop (Daniel et al. 1979). Live branches in higher initial planting densities are shorter and have small diameters (Smith and Strub 1991; Niemistö 1995; Mäkelä 1997; Mäkinen and Hein 2006; Wang et al. 2015; Hébert et al. 2016; Wang et al. 2018) and the height of the lowest branch is higher (Odabaºı et al. 2004; Kuehne et al. 2013). 
Similarly, in a study performed with common ash (Kuehne et al., 2013), the height of the lowest branch also increased with higher initial planting density. At a planting density of 3333 stem ha-1, a 4-m height of the lowest branch can be sufficient for the clear bole (>6 m). Since the average crown base height at the adjacent 32-year-old narrow-leaved ash plantation (3.7 × 3.7 m spacing) can reach up to 15-20 m (Özbayram and Çiçek 2018; Özbayram 2019), the height of the clear bole in this study can be expected to increase further.
It is stated that in some broadleaved species the maximum diameter of live branches increases as the spacing increases (Neilsen and Gerrand 1999; Mehari and Habte 2006). According to the present study, although the maximum diameter of dead branches was similar in all spacing treatments, the maximum diameter of live branches differed. Kuehne et al. (2013) reported that the maximum diameter of live and dead branches showed only a slight increase with increased spacing. In the present study, the difference between the maximum diameter of live branches for the narrowest and the widest spacing was 0.37 cm, while this difference was greater than 3.0 cm in the common ash (Kuehne et al. 2013). It can be said that at the initial planting density of 3333 stem ha-1, the maximum diameter of live branches did not significantly reduce the quality of the trees in the narrow-leaved ash plantation. 
Ash is one of the few species of deciduous trees that can be established in lowland stands, and in Turkey they are planted for the production of large-diameter and quality timber. Our results indicate that an initial planting density of 3333 trees per hectare should be applied for narrow-leaved ash plantations in lowland sites with high weed competition. Ash, perhaps as a silvicultural characteristic, can be more negatively affected by interspecific competition than by intraspecific competition. Initial planting densities of 2500 and 3333 stems per hectare are recommended in narrow-leaved ash plantations because the DBH, height, stand volume, height to lowest dead branch, and H/D ratio were similar for the two stockings. However, the cost of a planting density of 3333 trees per hectare (seedlings, planting, post-planting maintenance) will be higher; therefore, forest managers might instead prefer a planting density of 2500 stems per hectare (2.5 × 1.6 m).
Although the trees in the planting densities of 2500 and 3333 stems per hectare had reached the height and stem quality for the first thinning, no stand closure had occurred in the other initial planting densities. Thus, the first thinning at an early age can focus on higher planting densities, as well as the possibility of choosing a sufficient number and quality crop trees in the first thinning (mechanic or selective thinning).
Similar to the findings of planting interval studies on narrow-leaved ash in different growing environments, this study also recommends investigations into whether the growth and quality contributions provided by ecosilvi high planting density continue into an older age in these areas.
We would like to thank our colleagues (E. Çiçek, M. Yılmaz, D. Eºen, ª. Kulaç, B. Çetin and N. Çiçek) who set up the initial spacing trial in 2004 and the Scientific and Technological Research Council of Turkey (grant number TUBİTAK TOGTAG-3336) for supporting them. We give special thanks to the Akyazi Forest Enterprise Directorate for their permission and help. Special thanks are extended to Nuriye Peaci for English editing.
Alcorn, P. J., P. Pyttel, J. Bauhus, R. G. B. Smith, D. Thomas, R. James and A. Nicotra, 2007: Effects of initial planting density on branch development in 4-year-old plantation grown Eucalyptus pilularis and Eucalyptus cloeziana trees, Forest Ecology and Management, 252(1-3): 41-51.
Andrzejczyk, T., M. Liziniewicz and S. Drozdowski, 2015: Effect of spacing on growth and quality parameters in sessile oak (Quercus petraea) stands in central Poland: results 7 years after planting, Scandinavian Journal of Forest Research, 30(8): 710-718.
Assmann, E., 1970: Section B - Tree Growth and Form. In: E. Assmann ed. The Principles of Forest Yield Study. 39-81 p. Pergamon.