Plantation and application of fast-growing species, such as Populus deltoides increasingly, are common in the northern part of Iran. Concerns about decline in soil fertility and long-term productivity of fast-growing plantations have promoted interest in using nitrogen-fixing trees in mixed species plantations. P. deltoidesand Alnus glutinosa were planted in five proportions (100P, 70P:30A, 50P:50A, 30P:70A, 100A) in Foman, Iran. After 13 years, the effects of species interactions on tree growth and nutrient concentration in live and senescent leaves and soil properties were assessed. Diameter at breast height and total height of individualPopulus trees were positively affected by the presence of Alnus. Nitrogen concentrations in fully expanded and senescent leaves of Populus were higher in mixed plantations than monoculture plantations. The results of nutrition and nutrient return and growth indicated that mixed plantations of these two species were more productive and sustainable than their monoculture plantations. Within the framework of this experiment, it appeared that production was maximized when these two species were grown together in the relative proportions of 30% Populus and 70% Alnus.
Key words: Mixed plantation, Alnus, Populus, growth, soil.
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