The effect of planting intervals on the growth and wood production of white poplar (Populus alba L.) in the Mahabad nursery

Document Type : Research Paper

Authors

1 Department of Forest and Rangeland Research, West Azerbaijan Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and_Extension Organization (AREEO), Urmia, Iran.

2 Research Institute of Forests and Rangelands, Agricultural Research, Education and_Extension Organization (AREEO), Tehran, Iran.

3 Department of Forest Biological Sciences, Faculty of Natural Resources, Urmia University, Urmia, Iran.

10.22059/jfwp.2026.408900.1387

Abstract

Introduction: This study was designed to precisely evaluate the impact of three planting spacing patterns (1×2, 2×2, and 3×2 meters) on vegetative growth indicators and wood volume production in six selected white poplar clones, including improved cultivars 45.20, 44.9, 45.67, 45/77, and 44.13, as well as one local native clone, under semi-arid climatic conditions in western Iran. The ultimate goal was to identify the optimal clone and planting density combination to maximize yield per hectare, assess phenotypic stability, and determine the level of genetic control over volume traits.
Method: This field experiment was conducted at Dr. Javanshir Nursery in Mahabad, West Azerbaijan Province, using a split-plot arrangement based on a randomized complete block design with three replications over a four-year period. The main factor consisted of three planting spacing patterns: 1×2 meters (a density of five thousand trees per hectare), 2×2 meters, and 3×2 meters. The sub-factor included six white poplar clones. At the end of each growing season, collar diameter was measured using a digital caliper and total height using a height pole, while wood volume per tree was calculated using a cylindrical geometric model. Data analysis was performed using mixed linear models, Tukey's mean comparison test, best linear unbiased prediction methods, and biplot stability analysis. Furthermore, the broad-sense heritability coefficient for the wood volume trait was calculated.
Results: Analysis of variance demonstrated that the main effect of clone had a highly significant impact on all measured vegetative traits at the one percent probability level. Conversely, the main effect of planting spacing and the clone × spacing interaction were not statistically significant, indicating high phenotypic stability of the clones across different planting densities. Clones 45.20, 44.9, and particularly 44.13 recorded the highest single-tree wood volume production. Clone 13/44 achieved the maximum yield per hectare at the densest spacing (1×2 meters), with a planting density of five thousand trees per hectare, and, based on biplot analysis, exhibited the most consistent performance among all treatments. The broad-sense heritability coefficient for the wood volume trait was 0.78, highlighting the dominance of genetic factors over environmental variation and the excellent potential for selection based on phenotypic traits.
Conclusion: Based on the findings of this study, selecting appropriate clones plays a more decisive role than managing planting spacing in the success of white poplar timber cultivation projects under semi-arid conditions in western Iran. To achieve maximum economic efficiency and industrial wood production, planting clone 13/44 at the densest spacing pattern (1×2 meters) is recommended. This strategy maintains performance stability while maximizing yield per unit area, and the implementation of breeding programs focused on these cultivars is essential for the sustainable development of forestry agriculture in this climat

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References

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Forest and Wood Products
Volume 79, Issue 1
June 2026
Pages 67-80

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