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ŠUMARSKI LIST 5-6/2020 str. 48     <-- 48 -->        PDF

reported that some ash species (F. excelsior and F. angustifolia) are very sensitive to weed competition (Evans 1997; Kerr 2003; Boshier et al. 2005; Çicek et al. 2010). Nevertheless, narrow-leaved ash  exhibits the ability for fast growth, and the mean annual increment of stem wood over bark in Turkey can reach about 23 m3 ha–1 and 15 m3 ha–1 in plantations and natural stands, respectively (Kapucu et al. 1999).
In Turkey, almost all of the natural narrow-leaved ash dominated bottomland forests have been converted to pure narrow-leaved ash plantations over the last 60 years. The conversion is concentrated in the Adapazarı region, where the largest forests of this species are found (Çiçek 2004). Due to intensive weed competition, planting is preferred for the regeneration of the narrow-leaved ash  stands and establishment of new narrow-leaved ash plantations in Turkey. The demand for large-diameter narrow-leaved ash sawlogs and veneer logs (ø: 40‒60 cm) is high and thus, it is important to ensure optimal planting density in these plantations. Initial planting density is the most essential factor in determining the stocking, tree growth and quality, rotation periods, and management costs of a plantation establishment (Boydak 1992; Savill et al. 1997).
In Europe, the trend to use spacing of 3.0 × 3.0 m in broadleaved species has been reportedly increasing recently; however, in plantations of trees like ash, oak and beech, a planting density of at least 2500 stems per hectare is recommended in order to produce high-quality logs (Kerr 1995; Evans 1997; Boshier et al. 2005; Kuehne et al. 2013).  During the artificial regeneration of narrow-leaved ash  stands or the establishment of new narrow-leaved ash  plantations in the bottomlands in Turkey, spacings of 3.0 × 2.0 m and 3.0 × 2.5 m (1667-1333 stem ha-1) were used until 1980. In the 1980’s, spacings of 3.7 × 3.7 m ‒ 4.0 × 4.0 m (730 – 625 stem ha-1) and in the 1990’s and 2000’s spacings of 4.0 × 2.0 m (1250 stem ha-1) were used. As a result of this wide spacing, thick branches, knots, and trunks with low stem quality were formed. The narrow-leaved ash plantations established before 1980 produced better quality trees than the plantations established in later years (Çiçek and Yilmaz 2002b; Çiçek 2004).
In recent years, an initial planting density of 1111 stem ha-1 (3.0 × 3.0 m) has frequently been used in narrow-leaved ash plantations. Due to the low quality of the trees in existing narrow-leaved ash plantations and also due to the conditions of the growing environment (heavy weed competition), it is very important in silvicultural practice to determine the appropriate initial planting density of narrow-leaved ash. To this purpose, in Akyazı-Adapazarı, a region in Turkey where narrow-leaved ash  plantations are widespread, a long-term initial planting density trial was established in December 2004 with four different initial planting densities which included 1111, 1667, 2500 and 3333 stem ha-1 (Çicek et al. 2010). In this study, the ten-year results of this research were evaluated and the effects of initial planting density on the growth and quality parameters (tree shape, branch characteristic) of narrow-leaved ash trees were investigated.
MATERIAL AND METHODS
MATERIJALI I METODE
Study site – Područje istraživanja
The study site was established in the bottomlands of the Akyazı-Adapazarı region (40° 48’ N, 30° 33”E, 25 m) in Turkey. This was the site of a natural stand dominated by Narrow-leaved ash along with some other important broadleaved tree species (Ulmus laevis, Ulmus minor, Quercus robur, Acer campestre). However, the older natural stand had undergone clear-cut logging at the end of summer 2004 and the stumps were uprooted in the fall of 2004. After the stumps and slash were disposed of, the area was first ripped (60–80 cm soil depth) and then disked (20–30 cm soil depth) to aerate the soil.
The site has a deep alluvial soil and because of the heavy-textured soil the drainage is very poor. The soil pH varies at 7.5‒7.9 and the Ah horizon is very thin due to rapid decomposition. According to the Adapazarı meteorological station, the average annual precipitation is 846 mm and the average annual temperature is 14.3 °C. A water deficit is observed in the area during the summer period, while in some years the standing water level on the site may rise above ground level throughout November‒March, depending on the seasonal rainfall (Çicek et al. 2010).
Experimental Design and Initial Planting Density – Dizajn pokusa i početna gustoća sadnje
In December 2004, the experimental site (4.50 ha) was established in a randomized block design with three replications. The size of the experimental plots was 55 m × 66 m (3630 m2) (Figure 1) and four different initial planting densities were used (Table 1). The 1+0-year-old bare-rooted (65‒75 cm in height) narrow-leaved ash seedlings were produced in the Hendek nursery and planted in December 2004. Hand hoeing and disking were carried out around the seedlings for three years following the planting. In the first two years, 1-2% of the two-year narrow-leaved ash seedlings in the field had been damaged by animal browsing or frost (Çicek et al. 2010). These seedlings were stumped back to 8 cm above the root collar at the end of the second year. In May of the third year, singling was carried out on the stumped-back plants, leaving a healthy, straight stem. Two years after the stumping back, no difference was observed in height and diameter between the stumped and the non-stumped seedlings (Çicek and Tilki 2007).