The implementation of partial cutting harvesting systems is presenting regeneration challenges for forest managers across Canada.
By Jim Stirling
The emergence of partial cutting harvesting systems in Canada’s forests presents a complex range of issues surrounding their successful regeneration. The challenge is to provide data for forest managers to make informed decisions about creating viable new tree crops across a diversity of landscapes. Regeneration issues in partial cutting was the timely subject of recent workshops held in Kelowna and Prince George, British Columbia and Edmonton, Alberta. The challenges were outlined by the Silvicultural Operations Group of the western division of the Forest Engineering Research Institute of Canada (FERIC).
Each workshop brought together foresters and research scientists with multi-discipline backgrounds to offer insight into regenerating different partial cut situations. The three FERIC workshops shared common themes, but each agenda allowed participants to share in experiences of regional research projects. The Prince George workshop was held at the main campus of the University of Northern British Columbia. Steven Kiiskila kicked off the session saying that if partial cuts are defined as anything that is not a traditional clearcut, the number of regeneration variables and options can be considerable. It all depends on the goals at each site and how realistic they are, suggested the field agrologist with Pacific Regeneration Technologies’ Red Rock nursery near Prince George.
Kiiskila’s presentation centred on planting container seedlings in partial cuts, an environment where photosynthetic activity levels in seedlings changes more than in a clearcut. At the end of the day, planting stock large enough to overcome herbaceous vegetation competition in greater densities is recommended, he added. He noted larger seedlings are not a “magic bullet” and don’t always produce the best results. “We can plant trees, but long-term survival and growth in the understory remains to be seen.” Regenerating partial-cut harvesting areas is further complicated by elevation.
Mountain forests occupy about 14 million hectares in BC and are typically comprised of Englemann spruce and sub-alpine fir: the ESSF zone. About 15,000 hectares are logged annually in BC’s ESSF zone. Three silvicultural studies initiated in the early 1990s aimed to examine forest regeneration dynamics, explained Cleo Lajzerowicz, a silvicultural researcher with Industrial Forestry Service Ltd, in Prince George. The studies, near McBride, east of Likely in the Quesnel Highlands, and at Sicamous Creek, west of Salmon Arm, were widely separated. But there was a synthesis and cohesiveness of data across the large area that provides some comfort level for management, noted Lajzerowicz.
She concluded regeneration in partial cutting systems in the ESSF is possible. “Foresters need to have proper expectations for regeneration performance and must remember that these are snowy, cold, wet areas with short growing seasons and slow growing trees.” Alan Vyse added to the knowledge base with some early regeneration conclusions after winter logging at Sicamous Creek in 1994/95. The study looked at regeneration responses in individual tree selection, group selection (from 0.1 ha to 10 ha) and clear cutting after logging. Vyse is research forester emeritus with the Ministry of Forests’ Southern Interior Region. Healthy, growing trees were found in every cutting treatment, with the regeneration of spruce more successful than fir. Increasing opening size reduces natural regeneration but improves the performance of planted stock.
Exposure of mineral soil increased amounts of natural regeneration while also improving planted stock performance. The study also concluded expensive site preparation can be avoided if seedlings are planted in carefully selected sites immediately after logging. Vyse also offered interesting observations about wind and snow damage following partial and clear cutting. He believes damage in heavy snow years—characteristic in the region—contribute to snapping off stems in the stands. That has implications about what timber volumes might be expected from them. He said changes in the rates and types of damage through the 1994/95 to 2003 study period demonstrate the need for long-term monitoring. He noted levels of snapping and uprooting in partial cuts declined to the levels of an uncut stand by 1997, suggesting a period of stand adjustment. “Overall, we conclude there is no evidence supporting the belief that alternatives to large clearcuts will lead to increased wind damage,” says Vyse.
Other presentations to the workshop included preliminary results of a three-year study in tree generation response in a group shelterwood system of trembling aspen and white spruce in the Fort Nelson Forest District. The study indicated aspen natural regeneration was less in small openings but adequate enough to fully regenerate the site to aspen if that was the management objective. White spruce natural regeneration was very limited. Planted white spruce seedling heights in all treatments averaged 44 centimetres after three growing seasons. Denis Cormier, a senior researcher from FERIC’s eastern division in Pointe Claire, Quebec looked at choosing site preparation techniques in different partial cutting situations under Eastern Canadian conditions.
Site preparation after harvesting typically involves the use of skidders or bulldozers equipped with scarification rakes or spot scarification using excavators. Eastern trials indicate excavator use after harvesting is cost effective for smaller patches, while shallow scalping treatments with bulldozers is more effective for larger openings. Post-harvest treatment with an excavator is more attractive at higher spot densities in strip or selective cuts. Craig DeLong, a biologist with the Ministry of Forests in Prince George, adopted a holistic and futuristic view to his subject of underplanting aspen in the boreal forest.
DeLong’s hypothesis is to plant spruce under 40- to 60-year old aspen stands. When the spruce is 20 years old, the aspen is harvested while protecting the spruce. When the spruce is ready to harvest, it’s clear cut. The site is allowed to come back naturally with aspen, if enough exists, or managed as a spruce stand by planting. The advantage, says DeLong, is a cost-effective silvicultural system more consistent with the natural ecological dynamics of the boreal forest. However, adopting a landscape level management system where spruce flow would be maintained by underplanting aspen in unlogged areas would require changes in attitude and policy in BC.
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