Abstract
The paper deals with issues related to the regulation of the growing space of trees by thinning in poplar plantations of clone I-214, established on the best habitatat with a planting distance of 5 x 5 m, i.e. 400 trees per hectare, aged 11 years. On nine permanent experimental plots, which were formed in a random block design with three repetitions, the similarity of the growth elements of trees and plantations (H100, hL, D100, dg, N, G, V) were determined, as well as a small coefficient of variation of the number of trees between experimental plots (8.3%), indicating the homogeneity of the experiment as a whole. However, in experimental plots the variability of the breast height diameter (17.7-23.9%) and height (6.6-13.3%) were found, which is significantly higher than the expected variability in poplar plantations of similar age and density, which indicates the process of differentiation of trees in the plantation. The process of tree differentiation, determined in the first years since the establishment of the plantation, caused by gap filling with the seedlings after plantation establishment due to poor survival, continued more pronouncedly after closing the canopy of the trees in 6-7 years. Due to the intense tree competition in the crown layer, the process of differentiation of trees in the following period will be more intense, which will lead to the loss of trees left behind in growth, i.e., to loss in production. In order to reduce the losses due to natural mortality of trees, which in their established competitive relationship with more quality trees reduces their growth potential, thinnings were proposed, and the number of trees was experimentally reduced to 300 (EP-1) and 200 per hectare (EP-2). Thinnings were low (qd = 0,69-0,75), and the realized previous yield was 30 m3?ha-1 in EP-1 and 62 m3?ha-1 in EP-2. The value of the assortments of the realized previous yield is higher than the costs of thinning and costs related to the establishment of a plant with a larger number of trees by 250 ??ha-1 in EP-1, and by 515 ??ha-1 in EP-2, which indicates the economic justification of such a silvicultural measure.
Highlights
Poplars are fast-growing and light-demanding tree species whose growth significantly determines plantation density, i.e. the growing space of trees
In the plantation of poplar clone I-214, established in a favourable site at the planting distance of 5 x 5 m, i.e. 400 trees per hectare, at the age of 11 years in nine permanent experimental plots, a small variability between the mean and dominant amount of the growth elements of trees (H100, hL, diameters of 100 thickest trees per hectare (D100), dg), as well as between the total amount of the growth elements of the plantation (N, G, V) were determined, which indicates the homogeneity of the experiment as a whole
It is realistic to assume that the differentiation of trees in the control plot will continue at a more intense rate and will lead to the mortality of trees left behind in growth, i.e., to a loss in production
Summary
Poplars are fast-growing and light-demanding tree species whose growth significantly determines plantation density, i.e. the growing space of trees. This allows for the establishment of poplar plantations with different densities depending on the purpose of plantation, such as plantations for the production of logs, cellulose wood, and energy plantations (M a rkovi ć et al, 1997). Today dominate the plantations for the production of technical wood, as a result of the market demand for more valuable assortments due to closing the pulp and paper industry in Serbia. REGULATION OF SPACE FOR TREE GROWTH BY THINNING IN A POPLAR CLONE I-214 PLANTATION In comparison with Eastern Cottonwood clones (618, 457, 55/65, S6-36) at the age of 30 years, clone I-214 has similar production with more favorable participation of more valuable assortments (A n d ra š ev et al 2009).
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