Paper birch and lodgepole pine root reinforcement in coarse-, medium-, and fine-textured soils

The increased soil cohesion or reinforcement provided by roots varies among plant species and soil types. This study compared the contribution of paper birch (Betula papyrifera Marsh.) and lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) roots to soil shear resistance in two controlled environment experiments. Roots of paper birch and lodgepole pine trees contributed to a significant increase in soil shear resistance, regardless of soil type. At a shear depth of 0.20 to 0.44 m, paper birch contributed greater reinforcement than lodgepole pine. Both birch and pine provided the most root reinforcement in coarse-textured soil and the least reinforcement in medium-textured silt soil. Soil texture, porosity, and shear strength may have affected root branching of the two species, which in turn may have affected root reinforcement. At less than 1 year of age, paper birch trees planted as plugs can substantially increase soil shear strength compared with lodgepole pine in all soil types.