Alnus viridis seedlings were planted on placer mine spoil in an Alaskan subalpine watershed to bypass a seedling establishment bottleneck for A. viridis, and to evaluate the interaction between A. viridis and the dominant riparian woody plants, Salix alaxensis and Populus balsamifera. The study area was divided into 11 replicate blocks, each on a homogeneous recontoured spoil pile. Blocks were divided into two 0.01 ha plots, and treatments without (control) and with 84 planted A. viridis seedlings were randomly assigned to plots. After 10 years, the Alnus treatment had a dense stand of A. viridis 1–2 m tall, while the control had fewer, smaller seedlings. Compared to the control, planted A. viridis had a neutral effect on S. alaxensis and inhibited P. balsamifera at the seedling establishment stage, but facilitated the growth of established plants of both species, with many plants overtopping the A. viridis canopy. Compared to the control, S. alaxensis plants in the Alnus treatment had higher levels of foliar N and δ15N values closer to those of A. viridis, indicating the importance of N fixation by A. viridis. Planting A. viridis accelerated the rate of succession by stimulating growth of woody dominants.
