Growth of balsam poplar and black cottonwood in Alaska in relation to landform and soil

Abstract

While constructing site index curves for balsam poplar (Populus balsamifera L.) and western black cottonwood (Populus trichocarpa Torr. & A. Gray) for interior and southcentral Alaska, we found variations in growth patterns that appeared to be related to landform and soil properties. We characterized soils for 42 of 65 site index plots in an attempt to explain site productivity variation. We found significant negative correlations between site index and elevation. Region, landform, and floodplain characteristics (especially sediment deposition) significantly affected poplar growth rate and soil development patterns. Nutrient availability and recycling appear to be mediated by flooding through scouring or burial of surface organic layers. Soil pH patterns related to O-horizon development and salt crust formation and dissolution described previously for the Tanana River floodplain do not hold for all floodplains in Alaska. At similar latitudes and elevations, upland locations may have higher site indices than frequently sedimented floodplain locations because upland soil development is relatively uninterrupted. Floodplain locations experiencing little or no sediment accumulation after establishment of poplar stands tend to have higher site indices than those experiencing frequent sediment accumulation. At some floodplain locations, site index was positively correlated with rooting depth.