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Comparing Silvicultural Systems in a Coastal Montane Forest: Productivity and Cost of Harvesting Operations

Author(s) or contact(s): E.J. Phillips
Source: Research Branch
Subject: Silvicultural Systems
Series: FRDA Report
Other details:  Published 1996. Hardcopy is available.
 

Abstract

The Montane Alternative Silvicultural Systems (MASS) study is a multi-disciplinary, multi-agency project initiated both for silvicultural and social reasons. Concerns about regeneration performance in coastal montane forests, which lie between 700 and 1100 meters elevation, and public pressure to limit clearcutting in public forests prompted this research project. MacMillan Bloedel Limited, the Canadian Forest Service, and FERIC cooperated in the study, with participation by the University of Victoria and the University of British Columbia. FERIC received partial funding for its activities from the Canadian Forest Service's FRDA program and Green Plan.

Three alternative treatments representing a range of canopy removal levels were implemented in the MASS research area, located on the east coast of Vancouver Island in the Montane Moist Maritime Coastal Western Hemlock biogeoclimatic ecosystem. The three 9-ha treatments - uniform shelterwood, green tree retention, and patch cutting - were replicated three times. The study also included an old-growth and a clearcut control block. Harvesting, using the handfall/excavator forwarding technique, was completed in 1993. Post-harvest studies will continue for at least 20 years. FERIC monitored the productivity and cost of the falling and forwarding operations, and measured site disturbance and coarse woody debris for each harvesting treatment.

This trial showed that alternative harvesting treatments can be applied to old-growth forests on gentle terrain with reasonable falling and forwarding success. The combined cost of falling and forwarding were 10% higher for the patch cut ($7.88/m3) and green tree ($7.87/m3) treatments, and 38% higher for the shelterwood ($9.92/m3) treatment, compared to the clearcut ($7.19/m3). The cost of harvesting replicates within the same treatment were highly variable, due to differences in timber, terrain, and crew experience. The trial succeeded because the crew was willing to try new applications of existing skills.

The amount of downed woody biomass was generally consistent between treatments (413-477 m3 /ha); however, the distribution between decay classes was different. The shelterwood units had more material in the higher-decay classes, probably because more area was undisturbed, leaving the original woody material in place. The green-tree treatment had a higher level of solid wood because of greater breakage during falling and forwarding. To date, targets for post-harvest coarse woody debris levels have not been defined in British Columbia.

Dispersed site disturbance was roughly equal between treatments, with about 10% in the disturbed compacted category and about half of that at less than 10-cm depth. The whole soil bulk density sampling in deep tracks consistently showed an increase of approximately 10% compared to undisturbed areas. However, the densities were considered to be below the threshold for impeding root growth. The deep humus layers and the high slash loading protected the mineral soil from disturbance, and dispersed the weight of the harvesting equipment. The occupancy by roads was similar between the clearcut and the treatment area at 6.5 and 6.3% of total area.

Lower overall costs may be achieved with alternative silvicultural if free-to-grow standards can be met earlier and at less cost; however, the loss of the residual timber volume, tree marking costs, and additional supervision requirements must also be included in the equation.

Long term assessment of windthrow occurrence and regeneration success will answer some of the remaining question about the applicability of alternative silvicultural systems in the coastal montane forests of British Columbia.

FRDA Research Report 247 (1467 KB)

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Updated July 24, 2015