Determination of Optimal Density in Poplar (Populus deltoides) Plantations based on the Reineke Method (Case study: Guilan Province)

Density is a determinant and key factor in the development of a forest stand. In dense stands, competition is high, development occurred late due to limited access to resources, and are highly vulnerable to natural events such as insect infestation, fire, and drought. In contrast, low-density stands will not use the resources available in the habitat efficiently and the return of invested capital will decrease. Therefore, optimal density in forest stands is effective in the optimal use of resources in the habitat and maintaining health and growth in a stand. The present study was conducted to determine the optimal density in the afforestation stands of Populus deltoides in Guilan province and by selecting four pure stands of this species at different ages that had good distribution in the province.

The characteristics of the density (number per hectare of all trees) were counted and the diameter at breast height and the total height of trees were measured within one hectare (100 × 100 meters) area sampling plots. Stand Density Index (SDI) was calculated in order to evaluate the optimal amount of density based on allometric equations.

The results indicated that the existing density in Langrood (22 years of age with 5×5 m planting distance), Siahkal (29 years of age with 3×5 m planting distance ), Shaft (38 years of age with 3×3 m planting distance), and Talesh (37 years of age and 5×3.5 m planting distance) regions were 129, 216, 325, and 190, respectively; and the optimal density was 188, 259, 379, and 337 respectively in these areas. The results indicated that the existing density in Langrood, Siahkal, Shaft, and Talesh regions were 129, 216, 325, and 190, respectively; and the optimal density was 188, 259, 379, and 337 respectively; and having no significant difference (except in Talesh area) with existing density in these areas (p< 0.05). The existing density and the optimal density diagrams relative to the diameter classes showed that the diameter classes have a good density in lower classes, the two diagrams were very close to each other and there was overlap in the low classes. The 25 cm diameter class was observed as an intersection between the two diagrams. But, there was a greater difference between the optimal density and the existing density in the higher diameter classes.

The results of this study will be a suitable guide for easy and fast comparison between the existing and ideal density according to the species growing condition in the habitat, evaluation, and decision-making of appropriate management of trees density in afforestation.