Factors Affecting the Distribution of Populus balsamifera on the North Slope of Alaska, U.S.A

Balsam poplar (Populus balsamifera) groves occur north of the Brooks Range and treeline in arctic Alaska in a region of continuous permafrost and tundra vegetation. A poplar grove near the Ivishak River (69°06′N, 147°53′W) that we studied in detail contains 11 clones within 350 m of the river. Individual clones range from 600 to 4500 m2 in size and 90 to 200 yr in age. Poplar trees are larger in diameter in clones within 100 m of the river and less dense in clones away from the river. Unique soil thermal, moisture, and nutrient conditions may limit the expansion of poplar groves to only a few hundred meters from the river channel, including a “thaw bulb,” or depression in the permafrost table; lithologic discontinuities that concentrate moisture in the rooting zone; and accumulation of Ca-enriched precipitates from aufeis deposits. We prepared a map showing the distribution of poplar groves on the North Slope from published reports, satellite images, topographic maps, and observations of a bush pilot. The groves occur within an area bounded by 68–69°N and 142–154°W. A preliminary model explaining the origin and distribution of balsam poplar groves was developed from the case study; unpublished data; and a review of the geologic, hydrologic, and ecologic literature. The groves preferentially occur in areas where there is a sharp change in relief from the Brooks Range to the Arctic Foothills, extensive river braiding accompanied by geothermal springs and aufeis deposits, and a regional groundwater flow system enriched in Ca that may be controlled by faulting.