Harold J. Quesnel, PhD, P.Ag., R. P. Bio.
Ecotessera Consultants Ltd., 2701 Six Mile Lakes Rd., Nelson, BC V1L 6K8
Lauren Waters, RPF
L. Waters Ltd. Whitehorse, YK
The following is the Executive Summary taken from the complete report. Click here to download the complete report (410KB PDF format).
Alternative harvesting systems in old growth are being evaluated in the Revelstoke area. Integrating mountain caribou (Rangifer tarandus caribou) and timber management is important because a significant proportion of the annual allowable cut will be harvested from old-growth habitat critical for caribou in the Revelstoke area. Alternative silviculture systems that maintain caribou habitat while allowing access to merchantable timber are preferred in caribou management areas.
As part of a study on alternative harvesting systems, windthrow was evaluated at three sites north of Revelstoke. These sites are within the Interior Cedar-Hemlock zone and were harvested using a group selection (patch cut) silviculture system. Twenty-metre wide transects (or strip plots) were located around the perimeter of recently harvested small openings. Transects were also located in unharvested areas. Post-harvest results are presented for windthrow transects monitored for five years at the Keystone site, and for three years at Gregson Road and Lookout Mountain sites. At each site, the four treatments being compared are:
After five years at the Keystone site, there is no difference in the windthrow rate for total density and total basal area along the edge of group selections, in the unharvested buffers, and on the edge of small patches harvested along the boundaries of old clearcuts. Yearly rates for total windthrow density in the large unharvested area were comparable in magnitude to the unharvested buffer areas between the group selections. At the Keystone site, rates for total windthrow during 1998 were significantly greater than the rates for last three years of measurements. The lack of differences between treatments indicates that the edges of the 1-2 ha patches at this site are not suffering significantly more windthrow than unharvested areas. Analysis using data from the other two sites plus the large unharvested areas indicated that for three years, no significant differences existed between the four treatments. The only exception occurred the third year after harvesting. During that time period, the unharvested buffers had significantly less windthrow than the average for the inner and outer patches. For total density and total basal area of windthrow, the Keystone site had greater values than the other two sites for the three years after timber harvesting. The lowest rates occurred at the Lookout Mountain site. For the three sites studied, overall windthrow rates of 0.44-1.76 sph (0.08-0.96%)/yr, relative to the pre-harvested stand densities, are comparable to windthrow rates published for other mature or older forests. These rates indicate the relatively low frequency of windthrow north of Revelstoke during the past three years.
Windthrow rates for snags were unaffected by treatment. For example, the five year average for the large unharvested area at Keystone (0.90 sph) is comparable to values from the other three treatments (0.65-0.94 sph). The small patch harvesting in this study is not yielding a significantly greater rate of snag fall, relative to the large unharvested area. However, snags were more susceptible to windthrow than live trees. Pre-treatment stands were 7-11% dead while 40-62% of the windthrown trees were dead. These rates for dead trees were based on the first three years of harvesting across all three sites. Silvicultural systems in the study area, designed for wildlife management, will have to acknowledge and adjust for greater windthrow rates for snags.
Across all treatments and sites, most windthrown trees were western hemlock (Tsuga heterophylla) followed by western red cedar (Thuja plicata). A relatively high proportion of the stems of each species were dead. These windthrow rates by species generally reflect the species composition of the original, pre-treatment stand and are not a treatment effect. The orientation of windthrown trees and local valley systems indicate that easterly, followed by northerly or westerly winds, cause most of the windthrow on the Keystone site. The Gregson Road site has a similar pattern but lower rates. The Lookout Mountain site had low rates in all directions.
Columbia Mountains Institute of Applied Ecology
Box 2568 Revelstoke, B.C. V0E 2S0
Tel: 250-837-9311 Fax: 250-837-9311