Root biomass distribution under three cover types in a patchy Pseudotsuga menziesii forest in western Canada

We investigated the relationship between cover type and root biomass distribution and allocation to different root size classes in a naturally regenerated, dry, Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) forest in the southern interior of British Columbia, Canada. The site was selectively harvested 32 years previously; residual stems were 30 cm and 130-170 years old at breast height at the time of study. A total of nine pits (each measuring 1.0 m x 1.0 m) were excavated to a depth of 1.0 m under three different cover types: mature timber, grassy (Calamagrostis rubescens) openings (canopy gaps), and regeneration clumps. Total (all diameters) live root biomass ranged from 4.7 kg/m² under the mature timber to 1.9 kg/m ² under both regeneration clumps and grassy openings. Thin root (0.1 cm < φ ≤ 0.5 cm) biomass was similar across all three cover types (0. 8 kg/m²). We suggest that the similarity of thin root biomass across the three cover types is indicative of strong root competition at this resource-poor site: there appears to be no below-ground "root gap" corresponding to the canopy opening above the pinegrass-dominated patches.