Effects of Corylus cornuta Stem Density on Root Suckering and Rooting Depth of Populus tremuloides

Trembling aspen (Populus tremuloides Michx.) is capable of regenerating vegetatively through the formation of adventitious shoots (suckers) from roots. This field study investigated how sucker regeneration following harvest of aspen is affected by understories of beaked hazel (Corylus cornuta Marsh.). Aspen stands with a high density of understory hazel (\u3e45 000 stems per hectare (sph)) or a low density (\u3c5000 sph) were cut in the fall. After one growing season, aspen sucker density and growth were assessed. Soil trenches were excavated to examine the root density and rooting depth of both aspen and hazel. Aspen sucker regeneration was 68 200 sph in areas with low hazel density and 43 600 sph in areas with high hazel density; the cross-sectional surface area of aspen roots in shallow soil layers (0–10 cm) was significantly lower under high densities of hazel. As aspen usually produces most of its root suckers from shallow roots, the reduction of roots in the upper 10 cm of the soil was the likely cause of lower sucker densities. Height growth of the suckers was not influenced by pre-harvest hazel density, possibly owing to high light transmission as a result of the reduced leaf area of the hazel after the harvest