TechnicalForest Research Report Vancouver Forest Region 2100 Labieux Road, Nanaimo, BC, Canada, V9T 6E9, 250-751-7001 TR-007 Silviculture March 2001 Roberts Creek Study Forest Effects of Alternative Silvicultural Systems on Windthrow and Conifer Regeneration in a Coastal, Douglas-Fir-Dominated Forest: Summary of Year 3 Results By Brian DAnjou Research Silviculturist Research Disciplines: Ecology ~ Geology ~ Geomorphology ~ Hydrology ~ Pedology ~ Silviculture ~ Wildlife Brian D’Anjou Research Silviculturist Vancouver Forest Region BC Ministry of Forests 2100 Labieux Road Nanaimo, British Columbia V9T 6E9 250-751-7001 [email protected] http://www.for.gov.bc.ca/vancouvr/research/research_index.htm Technical Report TR-007 March 2001 Research Section, Vancouver Forest Region, BCMOF CONTENTS SUMMARY .......................................................................................................................................................................................... 2 KEYWORDS ....................................................................................................................................................................................... 2 ACKNOWLEDGEMENTS ................................................................................................................................................................ 2 INTRODUCTION ............................................................................................................................................................................... 3 STUDY AREA ..................................................................................................................................................................................... 3 STAND-MANAGEMENT OBJECTIVES ........................................................................................................................................ 4 DESCRIPTIONS OF THE SILVICULTURE PRESCRIPTIONS, PRE-HARVEST STAND STRUCTURE, AND HARVESTING .................................................................................................................................................................... 4 MEASUREMENTS ............................................................................................................................................................................. 5 Post-Harvest Stand Structure and Site Disturbance ................................................................................................................. 6 Windthrow .................................................................................................................................................................................... 6 Douglas-Fir Cone Crop and Conifer Seedfall ............................................................................................................................ 6 Minor Vegetation .......................................................................................................................................................................... 6 Natural Regeneration ................................................................................................................................................................... 7 Planted Regeneration ................................................................................................................................................................... 7 MANAGEMENT ISSUES RELATED TO ALTERNATIVE TREATMENTS.............................................................................. 9 Development of Planted and Natural Regeneration ................................................................................................................. 9 Windthrow .................................................................................................................................................................................... 9 CONCLUSIONS ................................................................................................................................................................................ 10 REFERENCES .................................................................................................................................................................................. 10 TABLES Table 1. Harvesting schedule in the extended-rotation system ....................................................................................................... 5 Table 2. Pre-harvest total stand volume and density, by treatment and as a percentage by species ............................................... 5 Table 3. Seedfall, by species, in unharvested control and dispersed retention ............................................................................... 7 Table 4. Density of post-harvest natural regeneration, by treatment and species ........................................................................... 8 FIGURES Figure 1. Location of the Roberts Creek Study Forest ................................................................................................................... 3 Figure 2. Allocation of treatments to blocks .................................................................................................................................. 5 Figure 3. Windthrow, three growing seasons after harvest, by treatment and species .................................................................... 6 Figure 4. Third-year cover of salal, fireweed, and bracken fern in control, dispersed retention, and clearcut .............................. 7 Figure 5. Three-year survival of planted seedlings, by species and treatment ............................................................................... 8 Figure 6. Height increment of planted regeneration during the three years after planting, by species and treatment .................... 8 Figure 7. Third-year height of planted regeneration and dominant natural regeneration: dispersed retention and clearcut .......... 9 Research Disciplines: Ecology ~ Geology ~ Geomorphology ~ Hydrology ~ Pedology ~ Silviculture ~ Wildlife 1 Technical Report TR-007 March 2001 Research Section, Vancouver Forest Region, BCMOF SUMMARY ment widened over time as third-year height growth (and stem caliper) in the clearcut was more than double that in Throughout the province of British Columbia, social, leg- other treatments. Increase in stem forking, chlorotic foliage, islative, and stewardship issues are driving forest manag- and stem-gall development on Douglas-fir under a dispersed ers to evaluate alternatives to clearcutting for harvesting overstory combined with growth reductions may affect long- and managing forests. In one example, three alternative term growth and yield of the understory plantation. silvicultural systems were established in a mature, mixed- conifer forest along the lower slopes of the Sunshine Composition of natural regeneration. Western hem- Coast just north of Vancouver. Within a 1-km2 area, a lock natural regeneration was enhanced beneath a dis- clearcut with reserves, dispersed retention (95 stems/ha persed overstory compared to that in a clearcut. The of dominant Douglas-fir and western redcedar), and ex- height-growth advantage of planted Douglas-fir and west- tended-rotation (11% volume removal in strips in initial ern redcedar over natural regeneration within a clearcut entry) were the harvesting systems prescribed, plus an was diminished beneath a dispersed overstory, and com- unharvested control. A single contractor harvested all three bined with increasing hemlock density, will necessitate blocks with Washington SLH78 mobile swing yarder be- early stocking control to maintain a Douglas-fir-domi- tween March 1996 and April 1997. Cable yarding resulted nated plantation. Increasing mineral-soil exposure should in little damage to the residual stand and caused little improve the establishment of Douglas-fir natural regen- disturbance to soil; mineral-soil exposure (<3%) was con- eration, but adequate seedfall is essential. Planting may fined yarding corridors. be the only method to ensure prompt establishment of western redcedar. Post-harvest monitoring of windthrow and regeneration (planted and natural) over six years identified issues as- KEYWORDS sociated with using dispersed retention to harvest these mature stands: forestry, forest management, adaptive management, har- vest planning, harvesting, silvicultural systems, Windthrow. Dispersed trees and trees along block clearcutting, dispersed retention, extended rotation, boundaries are prone to blowing down following the shelterwood, windthrow, stand structure, regeneration, first of the fall south-easterly winds. Over 22% of trees in seedfall, Douglas-fir, western hemlock, western redcedar, the dispersed retention blew down over three growing Vancouver Forest Region, British Columbia seasons, reducing stand density by 21 stems/ha. Tree manipulations, including topping and branch pruning, ACKNOWLEDGEMENTS and avoiding tree retention on wetter soils, are suggested methods for reducing windthrow. Paul Lawson completed the engineering tasks. Staff from the Sechelt field office of the Sunshine Coast Forest Dis- Growth and health of planted regeneration. trict (BC Ministry of Forests) provided critical assistance Growth of planted western redcedar and Douglas-fir was in dealing with the operational issues, and their contri- diminished beneath dispersed trees and within narrow butions are recognized. Steve Mitchell, Kerry