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ŠUMARSKI LIST 1-2/2019 str. 47     <-- 47 -->        PDF

Diameter increment distribution along the stem of narrow-leaved ash in response to thinning intensity
Porast promjera uzduž debla poljskog jasena kao reakcija na intenzitet proreda
Ali Kemal Özbayram
Narrow-leaved ash (NLA, Fraxinus angustifolia) is an important tree species due to its rapid development and valuable wood. In the pure NLA plantations in Turkey, little is known about the effects of thinning intensity on the diameter increment of different parts of the tree stem. In 2005, a thinning experiment with three thinning intensities (control: 0%; moderate: 19%; heavy: 28% of basal area removed) was established in an NLA plantation in Sakarya, Turkey. Seven years after thinning, a total of 25 sample trees representing dominant and co-dominant trees were felled, and cross-sectional stem samples were taken for analysis. The diameter at breast height (d1.30) and d1.30 increments of the co-dominant trees with the moderate and heavy treatments were similar to each other and greater than in the controls. The seven-year d1.30 increments of the dominant trees in the heavy-treatment plot were approximately 20% greater than in the other treatments plots. The highest diameter increments in both dominant and co-dominant trees for all treatments were determined at the 0.30 m and 17.30 m section heights. The sample tree diameter increments of between 1.30 m and 13.30 m were similar within their classes. In conclusion, heavy-intensity thinning of up to 28% did not cause tapering in the NLA plantation stems, and thus, heavy thinning can be recommended for NLA trees.
Key words: Narrow-leaved ash, Fraxinus angustifolia, thinning, stem form
In general, in order to keep the large and heavy stem standing, the bottom portion of a tree is thicker and heavier and the upper portions are thinner and lighter. However, there are mechanical and physiological factors that change the general shape of the stem (Gürocak, 2011). Mechanical effects such as wind and snow can cause the stem to either bend or break. When silvicultural treatments are carried out regularly in established stands, the stem’s resistance against mechanical effects is enhanced and a fuller stem shape is attained.
Thinning has been the most important silvicultural practice in broadleaved stands (Saatçioğlu, 1971) and can result in larger tree diameter, improved stem quality, increased merchantable volume and yield value and shortened rotation time (Hibbs et al., 1989; Mayor and Rodà, 1993; Cameron et al., 1995; Nowak, 1996; Oliver and Larson, 1996; Miller, 1997; Medhurst et al., 2001; Juodvalkis et al., 2005; Rytter and Werner, 2007). In broadleaved tree species the aim of