DIGITALNA ARHIVA ŠUMARSKOG LISTA
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tending candidates should be selected from the dominant trees that are 8 to 12 m tall. The initial large number of trees with high volume per hectare and heavy thinning at the ages of 32 and 40 have caused high values of the cutting yield, 115.13 m3∙ha-1 and 142.28 m3∙ha-1, which are in the category of the highest cutting yields achieved on individual experimental plots of young stands (Stojanović and Krstić, 1984; Vučković et al., 1990; Orlić 1999; Orlić et al., 1991). The applied thinnings had the highest intensity broadly recommended in the literature for spruce cultures of similar age (Halaj et al., 1986; Maunaga, 2001). In the period between the ages of 33 and 40, total of 555 trees per hectare were cut down due to mortality and snow-breaks (14.2%). Their volume was 22.0 m3∙ha-1. Thus it follows that out of the initial number of trees, a total of 1,933 trees was cut down (49.4%) in the 32nd year of age. Their total volume was 137.1 m3∙ha-1 (35.9%). The research of Valinger and Petersson (1996) carried out on permanent experimental plots established in 24-45-year-old spruce cultures suggests that the greatest relative number of trees damaged by snow and wind was recorded on control plots and in the early period after extremely heavy thinnings (over 40% of basal area). According to these results, the increased risk of damage caused by snow and wind is greatly affected by the unfavourable position of the culture and high culture density, which is consistent with our research. In the period between the ages of 33 and 40, the reaction in the diameter increment of the remaining trees was weak. Compared to the results of Stojanović and Krstić (1984), the current diameter increment of the remaining trees after the thinning, between the ages of 33 and 40 (0.31 cm∙year.-1, Table 7), was similar to the value of the diameter increment on the control area with a 30% higher number of trees per hectare in the two five-year age periods between the stand ages of 32 and 42 (0.31 to 0.34 cm∙year-1). The current diameter increment of the future trees in the investigated culture (0.54 cm∙year-1, Table 7) was within the range of the increment of remaining trees on the experimental plots with the thinnings of light to moderate intensity stated by Stojanović and Krstić (1984). The size of the diameter increment of the aspirant trees in the researched culture between the ages of 33 and 40 was significantly lower than the sizes stated by Štefančík (2012) for the thinning procedures first implemented at the stand age of 20. In the period after thinning was performed in the investigated culture, between the ages of 33 and 40, the current volume increment was 22.15 m3∙ha-1∙year-1 and it was similar to the increment found by Orlić (1999) in 41-year-old spruce cultures with about 40% smaller number of trees after a thinning at the age of 32. Compared to the sizes of the current increment of basal area and volume stated by Stojanović and Krstić (1984), which were achieved at a similar age and with the application of light to moderate thinning from below, the increments in the investigated culture were 35% smaller. Compared to data provided by Slodičák and Novak (2003), who conducted light selective thinnings at a similar age on a series of experimental areas in spruce stands of approximately the same age, basal area increments per hectare in the investigated culture were higher by 13-166%. The second thinning at the age of 40 and at the height of dominant trees over 20 m was low (qd <0.85) heavy (34% of the volume) selective thinning. The heavy thinning at the age of 40 with the thinning volume of 142.28 m3∙ha-1 caused a greater diameter increment, i.e. better reaction in the diameter increment of the remaining trees, compared to the thinning at the age of 32. The future trees had a 28% higher diameter increment in the age period between 41 and 50 years compared to the age period between 33 and 40. The difference in the diameter increment size between the two study periods in the investigated stand is in line with other authors` results that spruce stands on favourable sites and with the number of trees that is not too large for the given age react positively to thinning even if they are performed later in life (Makinen and Isomaki, 2004a; 2004b; Preuhsler and Schmidt, 1989). According to the results (Preushler and Schmidt, 1989), late moderate to heavy thinnings from below in densely closed spruce stands, aged 48 and 58 years, exhibit a slower reaction in the volume increment in the early period after the cutting (5-7 years) compared to the following five-year period, which is consistent with our research. According to the results of Stojanović and Krstić (1984) that refer to the stand age between 32 and 42, larger diameter (11%) and volume (20%) increments in the second five-year period than in the first were identified only on the heavily thinned experimental plots. On the experimental plots with light to moderate first thinning and light second thinning, the mentioned autors recorded smaller diameter, basal area and volume increments in the second than in the first observed (five-year) period. The higher increment in the later age period, between the ages of 50 and 70 years, is related to a small number of trees per hectare in spruce monocultures. Slodičák and Novak (2003) noted increment increase in the later period, after heavy thinning from below, while Štefančík (2012) stresses that heavy thinning, particularly selective thinning, increases the diameter increment of target trees. In the case of heavy and very heavy thinning from below, larger increase in diameter increment was also observed after the second compared to the period after the first thinning (Nilsson et al., 2010). On several series of experimental plots in several decades of research (over 100 years) in spruce stands, it has been found that if the stands are young and if we apply light to moderate thinning from below in a short period of time, they will achieve higher increments of basal area (and volume) per hectare than control plots. Further, similar values |