Partial cutting of second growth western hemlock on Vancouver Island
Creators: name: Clark, Marvin Lloyd
Publisher: name: University of British Columbia
Year: 2009

description: As the harvest of old-growth forests of coastal British Columbia declines, forest companies are considering partial cutting methods to augment fiber supplies. However, the operational and economic feasibility of many of these options has yet to be proven. This thesis investigates the harvesting and economic implications associated with the partial cutting of second growth western hemlock stands in coastal British Columbia. Specifically, it examines two partial cutting options for immature forests; commercial thinning and shelterwood havesting. The results presented are based on data acquired during an operational trial conducted between January 1997 and October 1998 by the Port McNeill Division of MacMillan Bloedel Limited, on northern Vancouver Island. The thesis is presented in two parts. Part I includes case study results while Part II investigates economic analyses using case study data. The specific objectives are: to evaluate productivity, cost and factors influencing combinations of cable and groundbased harvesting systems, to document the effectiveness of falling and yarding techniques for the treatments, to document extent, severity, and causes of post-harvest site disturbance, wind damage, and residual tree wounding, to compare the net present value of harvesting strategies that include: clearcut at 53 years, clearcut at financial rotation age, clearcut at stand culmination age, and partial cut to four residual stand densities (450, 300,200 and 100 trees/ha) at age 53, to determine the financial consequences of residual tree wounding for partial cuts at final harvest age using net present value analysis, and to discuss the potential to use Multiple Account Benefit-Cost Evaluation to compare the socio-economic implications of different harvesting options. The case study demonstrated that both cable and ground-based harvesting systems are operationally feasible for second growth hemlock stands. However, a number of factors in the falling and extraction phases need to be considered to ensure operational viability. Both manual and mechanized falling methods were monitored and manual falling proved more cost effective and provided better residual stand quality. However, it is recognized that mechanical falling is a safer method. Two types of extraction were observed at Port McNeill. A standing skyline cable system was used to harvest three treatment blocks and a ground-based hydraulic log loader was used to forward the logs from the fourth treatment block. Both systems were effective for the site, stand, and weather conditions in this trial. Stand and site impacts for the Port McNeill case study were assessed through post-harvest surveys for wind damage, site disturbance, and residual tree wounding. Unfortunately, a catastrophic windstorm caused extensive damage to the study area when harvesting was only partially completed, and the target stand densities on the treatment units had to be modified. Because both initial harvesting and windfall salvage were carried out, it is not possible to make comparisons between treatments for site disturbance and residual stand damage. The net present values (NPV) of three clearcut and four partial cut harvesting scenarios were compared using the results of the case study. Under the assumptions used in this analysis, NPVs were greatest for the clearcut scenarios and varied inversely with stand age at the time of clearcutting. For the partial cut scenarios, the treatment with the lowest residual density (SW100) provided the greatest NPV. The financial implications of residual tree wounding in partial cuts were examined using NPV analysis. The outcome identified that the final harvest NPVs were quite insensitive to wounding levels. This result is encouraging in that residual tree wounding may not be as financially significant as is currently perceived by the forestry community. This thesis presents an example of how Multiple Account Analysis can be used to compare alternative harvesting methods and made tradeoffs between competing solutions. Because there is a growing trend towards non-economic constraints influencing harvest prescriptions in coastal B.C., it will become more critical for forest managers to rank harvesting alternatives using methods that consider the criteria of all stakeholders equitably.