DIGITALNA ARHIVA ŠUMARSKOG LISTA

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ŠUMARSKI LIST 11-12/2009 str. 37 <-- 37 --> PDF |

S.Andrašev, M. Bobinac, S. Orlović: DIAMETER STRUCTURE MODELS OF BLACK POPLAR SELECTED ... Šumarski list br. 11–12, CXXXIII (2009), 589-603 The practical significance of the obtained models is best seen by the example of estimating the percentage of the number of trees with diameters at breast height above 40 cm.The diameter at breast height above 40 cm makes it possible to produce the best quality veneer logs (Pudar, 1986; Krznar,1987), so the share of such trees indicates indirectly the plantation value. Table 10 presents the mean relative percentage of the number of trees with diameters at breast height above 40 cm from the diameter structure model and the results of the analysis of variance test and LSD test at the 0.05 risk level.The analysis of variance points out the signi th ficant differences between the clones, both in the 17 th and in the 20 year. Significantly the highest percentage of the number of trees with diameters at breast height above 40 cm was attained by the clone PE 19/66, and the lowest percentage by the clones S and S . 6-7 6-36 5. DISCUSSION – Rasprava The researched plantation of six newly selected clones showed different values of stand quadratic mean diameter (dg) and total basal area per hectare (G) at the end of the study period (20 years). Based on the results of LSD test at the 5%risk level, the clones were grouped in several production groups.Also, the periodical measurements of diameter at breast height showed different diameter growth of the clones depending on the age. In the initial period, the clonesPopulus deltoides Bartr. ex Marsh. (S , NS , PE 19/66, NS , S ) developed more intensively than the clone Pannonia (Populus × euramericana (Dode) Guinier). In the later period, Pannonia developed more intensively and the clones ofP.deltoidesBartr. ex Marsh. showed the differentiation. The different growth characteristics of the clonesP.deltoidesBartr. ex Marsh. and P.×euramericana( Dode) Guinier, prevent the reliable productivity differentiation of the clones before the ages of 16–18 years at plantation density of 400 trees per hectare (Andrašev, 2008). Taking into account the above facts, the differentiation of study poplar clones by total basal area per hectare (G) and stand quadratic mean diameter (dg) at the ages of 17 and 20 years showed (LSD test) that clone PE 19/66 can be classified in one group, and the other clones in the other group. The constructed Weibull models of diameter structure, and the derived percentage of the number trees with diameters at breast height above 40 cm (Nd>40cm [%]) confirmed thegrouping of the clones in two groups, as well as based on growth elements (G,dg), which point out their implementation in productive differentiation. The study results refer to six black poplar clones, SectionAigeiros(Duby), four of which were registered as cultivars in Serbia, and the other two are still undergoing the selection procedure.The registered poplar clones (S , NS , NS and Pannonia) attained similar 6-7 1-3 11-8 6-36 6-36 1-3 11-8 plantation growth elements (dg ,G), and diameter structure, which was confirmed by statistical tests.The other two clones which were in selection procedure (S and 6-7 PE 19/66) attained significant differences in growth elements and plantation structure.Clone S did not have 6-7 significantly lower values of growth elements and structure compared to registered clones. However, clone PE 19/66 attained a significant advantage in the elements of growth and structure compared to the registered clones at the plantation age of 20 years, which, according toMarkovićet al.(1997) andAndrašev (2008), can be taken as the rotation period for the density of 400 trees per hectare, so this clone is a reliable candidate for a soon registration and putting in mass production. The study results indicate that theWeibull diameter structure model can be successfully applied in the estimation of diameter structure of the newly selected poplar clones at different plantation ages. The application of the model of theWeibull three- parameter distribution, especially the calculation of the location parameter (a), was made difficult and it was evaluated in different ways: using different mathematical expressions (Zarnoch andDell,1985), fixed values of location parameter 0 or d , the percentiles of min minimal diameter, with frequent value 50%·d (Bai min ley and Dell, 1973, Knoebel, et al, 1986, Lei, 2008). Our research indicates that the choice of location parameter (a) inWeibull distribution should not be uniformly defined, and that further research is necessary aiming at reliable methods of diameter structure modelling in poplar plantations. Taking into account the so-called “biological”interpretation of the calculated parameters, it can be concluded that location parameter (a) is the minimal diameter in the plantation (but not also in the sample based on which it is predicted). In most clones, location parameters depending on the age show an increasing trend; in the initial period the trend is sharp (till the age of 5), and later on it is slower or more intensive, depending on the clone.The above can be related to the so-called “solitary growth”in the initial period before crown closure (from fifth to eighth year) and the so-called “stand growth”with the competitive impact of trees.The observed significant drop of location parameter (a) in the clone PE 19/66 is the consequence of the applied method and it shows that in periodical measurements the so-called “biological component”should be “incorporated” in its definition. The scale parameter (b) is in high correlation (R=0.884) with the variability of diameters at breast |