Stevenson, Susan K.

"The wetter subzones of the Interior Cedar-Hemlock (ICH) zone are naturally dominated by old forests in which trees regenerate and grow in small gaps in the forest canopy. Increased interest in ecosystem-based management has led to interest in the use of partial cutting systems, rather than clearcutting, in wet cedar-hemlock stands. Application of group selection and other silvicultural systems is most effective if it is supported by knowledge of the structure and dynamics of these forests, as well as the effects of partial cutting on resource values. To address this information need, we have established a partial cutting trial in the Quesnel Highland. We measured attributes, including wildlife habitat attributes, of standing trees and logs on the forest floor in the pre-harvest old-growth stand. We measured tree growth rates from samples taken from sound stumps scattered throughout the harvested area, including an 81- to 100-year-old stand as well as the old-growth stand. Stumps of Douglas-fir trees up to 439 years were found. Western redcedar appears to have been a major component throughout the history of the old-growth stand, whereas Douglas-fir is in decline, and western hemlock is increasing. Growth rates of western redcedar, western hemlock and subalpine fir varied greatly from one individual to another, and within the lifespan of a single individual, probably reflecting the variety of microhabitats occupied by these species in a stand where trees regenerate under the canopy. The occurrence of wildlife habitat attributes in standing trees varied by tree species, and increased with diameter. Partial cutting silvicultural systems have the potential of maintaining some of the attributes associated with old-growth stands, but only if the stands are managed so that a significant component of old trees is present in the stand at all times."

"Partial cutting systems have often been proposed as a means of maintaining canopy lichen abundance and diversity in managed forests. However, most assessments of the effectiveness of specific harvest practices in maintain canopy lichens are based on immediate post-harvest measurements. Fewer assessments extend beyond the immediate 2-3 year post-harvest period. We anticipate that changes in lichen community composition will occur for many decades after harvesting, as lichens respond over time to changes in canopy microclimate and substrate availability. We can now report on the response of canopy lichen communities 10 years after partial cutting at Pinkerton Mountain, in B.C.’s central interior, where 30% of the timber volume had been removed in a side-by-side comparison of two partial-cut harvesting treatments: one in which trees were removed in patches, as part of a group selection silvicultural system, and one in which trees were removed singly from throughout the harvest unit, as part of a single tree selection silvicultural system. Our measurements show a shift in canopy lichen genus composition, with the proportion of Bryoria – the preferred winter forage of the red-listed mountain caribou – gradually increasing in relation to Alectoria. However, it will still be many decades before overall forage lichen loading in the partial cut harvest stands approaches that of uncut adjacent old-growth forests. Thus, although partial cut harvesting is an effective strategy for maintaining winter forage for mountain caribou, it cannot substitute for maintaining core habitat in a natural state."