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| ŠUMARSKI LIST 5-6/2018 str. 53 <-- 53 --> PDF |
volume index observed in the pruned ramets. It was assumed that ramets surpressed the middle-aged seed orchard developed different physiological strategies as a result of different morphological structures. Although the diameters at breast height of control ramets in the middle-aged seed orchard were larger than the pruned ramets in the first two years (2012 and 2013), it dropped behind in the following two years (2014 and 2015). While these changes were taking place in the diameters at breast height, control ramets continued to remain taller than the pruned ramets throughout these four years. This was assumed to be a result of the faster growth in the crowns of the pruned ramets. It was also assumed that the increase in the size of crowns led to an increase in the volume index, which in turn lead to an increase in the area of photosynthesis that resulted in higher diameters. Accordingly, the volume indices of pruned ramets have always been higher than that of control ramets in each year between 2012 and 2015. It was thought that the need of thinning arose in the previous years, and that the pruning of ramets at one node in 2008 lead to the development of their crowns. This, in turn, led the pruned ramets to have a larger volume index during the entire four-year period. Moreover, as the ramets were pruned by a node in 2008, their height decreased 134 cm (26%) on average, and the difference between the heights of control and pruned ramets were 71 cm (Alan et al. 2011). There was no statistically significant difference between control ramets and ramets pruned by one node in terms of their three-year conelet and cone production. In other words, the ramets that were pruned and shortened heights (average 125 cm) produced the same amount of conelets and cones with control ramets; however, the quantity of conelets and cones in the middle-aged seed orchard was lower than that in the young seed orchard. This finding was assumed to be due to the fact that the ramets in the middle-aged seed orchard were packed very densely, which indicated that, even though they had developed their crown diameters as a result of pruning, they still required thinning. In the young seed orchard, the four-year averages of height, diameter at breast height and volume index was larger in the control ramets than in the ramets whose terminal shoots were pruned. Nevertheless, the difference between the heights of control ramets and of the ramets whose terminal shoots were pruned dropped from 153 cm in 2012 to 92 cm in 2015, indicating that pruned ramets had grown proportionally faster than the unpruned ramets. Similarly, Greenwood and Bramlett (1989) observed that when ramets over two and three meters height were top pruned in a young loblolly pine seed orchard, their average heights decreased by 12 to 33%, while their average diameter at breast height decreased by 6 to 18%. In light of this information, it was understood that pruning in young seed orchards not only led to a decline in height, but also to a reduction in diameter at breast height. The young seed orchard had not yet reached maturity (eight years), which is required for conelet and cone production. However, it still produced more conelets and cones than the middle-aged seed orchard. In both seed orchards, 5×5 m of spacing was used; however, even though the stand density in the middle-aged seed orchards was high, the same situation was not observed in the young seed orchard. It was understood that the high stand density in the middle-aged seed orchard lead to an overall reduction in the amount of light received, which in turn prevented crown development. In the young seed orchard, no difference was observed between the untreated controls and pruned ramets in terms of conelet and cone production. Matheson and Willcocks (1976) concluded that the yield and age of production of Pinus radiata seed orchards increased with top pruning. Similarly, Nienstaedt (1981) also suggested that top pruning increases seed yield, and thus reduces costs, and that reduced tree height has made seed collection easier and safer. While Gerwig (1987) concluded that top pruning enables the control of tree height, he also pointed out that the effect of pruning on cone production varies according to tree species, age and the degree of pruning. On the other hand, studies have also emphasized the importance of beginning to shape the tree crown by pruning at a young age, and of increasing the flowering parts by creating a denser crown (Stoehr et al. 1995; Smith 2004). Kolpak et al. (2015) reported that, as an alternative to conventional seed orchards, they developed miniaturized seed orchards with Douglas-fir. In these seed orchards (five to seven years old) modeled on fruit orchards, researchers topped the ramets every two years, suggesting that the removal of flower buds affected the physiologies of the clones; however, they did not identify a significant difference between pruned and unpruned clones in terms of productivity (female flower, male flower). On the other hand, Stoehr et al. (1995) showed that cone production dropped considerably in severely topped (50%) clone with respect to the untreated clones in a young lodgepole pine seed orchard, revealing that severe pruning did not yield in favorable results in young seed orchards. Then again, Gerwig (1987) indicated that pruning of trees every year for five years in a young and yet unproductive loblolly pineseed orchard shortened height by 300 cm with respect to unpruned controls, and led to an acceptable reduction in average yield; however, he also highlighted that pruning done in mid-summer instead of spring led to relatively better results. In a study in which leading shoots were pruned at different regimes for six years in a Douglas-fir seed orchard, Copes (1973) decided to repeat the pruning process at the end of each year. Similarly, in a study conducted with western larch, results suggested that the best |