Three replicates of a uniform shelterwood trial were established in even-aged stands dominated by Douglas-fir in the SBSdw1 variant northeast of Williams Lake, B.C., with initial harvesting conducted in the summer of 1991. Treatments consisted of a two-stage shelterwood leaving 50% residual basal area (RBA) after the first entry and a three-stage shelterwood leaving 70% RBA, with overstory thinning achieved by hand-falling or by feller-buncher. Treatment units were 1.4 ha in area, with an uncut control (100% RBA) at each site. Seedfall was monitored using ten 0.37 m 2 seedfall traps in each treatment unit, inspected twice a year from 1992 through 1998. The abundance of different ground surface materials was surveyed in 1990, 1991, and 1993. Controlled germination experiments were conducted in 1994, 1995, and 1996. on four seedbed materials (forest floor, live moss, rotting wood, and mineral soil) across all RBA levels. Surveys of the density of natural regeneration were conducted in 1990, 1991, 1993, 1994, and 1996.
Douglas-fir, hybrid white spruce, lodgepole pine, and subalpine fir all exhibited their best germination on rotting wood, followed by mineral soil, intact forest floor, and live moss mats. The first-year survival of new seedlings likewise was greatest on rotting wood and mineral soil, with the poorest germinant survival on moss mats. Survival of spruce and pine germinants on intact forest floor was intermediate, but Douglas-fir and subalpine fir germinant survival on intact forest floor did not differ significantly from that observed on rotting wood and mineral soil. Germination and early survival on organic seedbeds was negatively correlated with high light availability and with moisture stress near the surface.
All treatments were successful in producing dense new Douglas-fir regeneration and in protecting them from growing-season frosts. No significant differences in the density of all Douglas-fir regeneration, or seedlings established since logging, were observed among the four alternative treatments and the uncut control during the first 5 years after logging. Treatments with 50% RBA and those logged by feller-buncher supported significantly higher densities of some categories of regeneration. Continued monitoring is needed to evaluate these treatments further, and results will change after the seed cut (second entry) is implemented in 2001 for the 70% RBA treatment. Results to date suggest that a low residual basal area, combined with a high level of forest floor disturbance, is preferable for enhancing conifer regeneration. It is tentatively recommended that a preparatory cut is not necessary for naturally regenerating Douglas-fir under a shelterwood overstory in this zone, and that the seed cut should leave less than 50% residual basal area.
Working Paper 47 (5962 KB)
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Updated July 24, 2015