Establishment of four Salicaceae species on river bars in interior Alaska

Patterns of seed and vegetative reproduction were investigated for three floodplain species, balsam poplar Populus balsamifera L., feltleaf willow Salix alaxensis (Anderss.) Cov. and sandbar willow Salix interior Rowlee, and one upland species, trembling aspen Populus tremuloides Michx., in interior Alaska. All four species have similar patterns of seed germination in response to moisture stress and high salt concentrations when tested under laboratory conditions. In field experiments, percent germination of all four species was also very similar, ranging from 0% on dry sandy sites, to greater than 60% on mesic silty sites. Germination on salt crusts ranged from 0–40% for all species, depending on the physical characteristics of the soil surface. Colonization of mesic silty sites was almost exclusively by seed, whereas colonization of dry sandy sites was limited to those species which were able to root sucker under floodplain conditions. Root suckering was also an important means of establishment on frequently inundated sites where establishment by seed was limited by flooding. Differences between the species in their distribution on the floodplain were related to differences in patterns of vegetative reproduction, but not seed germination.