A uniform shelterwood systems trial was established in 1990 to test overstorey tree retention levels required to naturally regenerate Douglas-fir (Pseudotsuga menziesii var. glauca) on frost-prone sites in the Dry Warm Sub-Boreal Spruce (SBSdw) biogeoclimatic subzone of central British Columbia. Two or three harvest entries were used to create combinations of preparatory and regeneration cuts that affected seedfall and vegetation, plus density and growth of both natural and planted Douglas-fir regeneration. A regeneration cut (30 m?/ha residual basal area [RBA]) in 1991, a regeneration cut (1991) followed by a second regeneration cut (15 m?/ha RBA) in 2001, and preparatory cut (40 m?/ha RBA) (1991) followed by a regeneration cut (20 m?/ha RBA) in 2001 were successful at establishing and growing regeneration of sufficient density and size to meet stocking targets in a 20-year period on most sites. The density and growth of the main cohort of Douglas-fir regeneration (> 100 cm tall) increased with decreasing RBA, reflective of improved light conditions. Frost damage was inconsequential in all shelterwood treatment combinations, while clearcutting of the no-harvest controls (60 m?/ha RBA) in 2011 resulted in extensive frost damage to planted Douglas-fir regeneration. Vegetation competition was effectively controlled in the shelterwood treatments except for advance subalpine fir (Abies lasiocarpa) regeneration, which was cut at the second harvest entry. Douglas-fir seed crops occurred frequently (every 3-4 years) with high quantities of viable seed, ensuring natural regeneration. The shelterwood silvicultural systems tested in this study provide foresters with several options to establish and grow Douglas-fir regeneration to meet land management objectives.
Michaela J. Waterhouse, Karen E. Baleshta, Amanda F. Linnell Nemec. 2021. Application of Uniform Shelterwood Silvicultural Systems in the Sub-Boreal Spruce Biogeoclimatic Zone in Central British Columbia. FLNRORD. Technical Report (FLNRORD). TR131