عنوان مقاله [English]
Poplars are fast-growing species that were planted pure in the past. Mixed plantations of poplar with nitrogen fixing species have been recommended recently to increase the soil fertility. In this study, American poplar (Populus deltoids 77/51) has been planted with different mixture ratios with Caucasian Alder (Alnus subcordata) in randomized complete blocks with four replications in Chamestan research station, Mazandaran province, northern Iran. For further comparisons, pure stands of poplar and alder were also added to the treatment design. The plantation spacing was 4×4m. Results after 7 years showed that survival rate of poplar were greater than alder, in general. The highest rate of poplar survival was observed in the treatment of 50% poplar + 50% alder. The differences among treatments were statistically significant. The highest diameter increment was measured within poplars in the treatment of 33% poplar + 67% alder and the least in the pure poplar stand. The highest total height was measured within poplars in the treatment of 67% poplar + 33% alder. The highest volume of individuals trees were measured within poplars in the mixture of 33% poplar + 67% alder, while the highest tree volume of alder was obtained within the alder pure stand. The amount of soil nitrogen was significantly higher in the pure alder stand and mixture of 33% poplar + 67% alder, than in the soil of other treatments.