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Managing The Mix 

A mixed wood management trial in Alberta between Ainsworth Lumber and Weyerhaeuser is showing a very positive spruce release effect.

By Tony Kryzanowski 

Recovering aspen from mixed stands in Canada's boreal forest resembles a search and rescue mission. Foresters search for aspen stands that are in danger of being overwhelmed by the conifer understorey and harvest them before they become chipmunk housing. The extraction process must occur without significant damage to the valuable surrounding conifer resource. At present, any mixed stand with an understorey of greater than 250 conifer stems per hectare would be managed on a conifer rotation. By the time the understorey reaches rotation age, the deciduous overstorey dies off as part of natural succession. The cooperative effort currently underway in the Grande Prairie, Alberta area between Ainsworth Lumber and Weyerhaeuser Canada to harvest aspen-at the same time protecting the spruce understorey-is one of a growing number of mixed stand management trials that are fairly well advanced or in their initial stages. 

Grant Williamson, Ainsworth divisional operations superintendent, (above) and a cutting sample taken from spruce in the first trial cutblock. The sample illustrates the release effect on the spruce once most of the aspen was removed

Ainsworth owns the deciduous harvesting rights while Weyerhaeuser owns the coniferous rights on a significant overlapping land base. But why this sudden interest in deciduous harvesting and coniferous understorey protection? For a start, the preliminary results from ongoing research studies show that the amount of aspen recovery and resulting incremental conifer growth can be nothing short of astounding. Further research is needed, however, to ensure the growth and yield effects are clearly understood. "There are a lot of companies that are interested in this kind of forest management," says Ainsworth divisional operations superintendent Grant Williamson. "In Alberta and in probably most of the other provinces, both the deciduous and coniferous resource has a value. And rather than try to fight Mother Nature, we see there's some real advantages to trying to manage these stands." 

He supports the approach of managing mixed wood stands as they exist in overlapping areas between deciduous and coniferous consumers, rather than separating that land base into one or the other. "I don't think in the long run that separating is the right thing to do," he says. "In the long run we'll both gain in terms of annual allowable cut and cost by trying to manage these mixed wood stands as mixed wood stands." For both deciduous and coniferous consumers, mixed stand management trials have the potential of yielding hidden mother lodes of extra fibre within the existing annual allowable cuts-it's a bit like finding extra fibre. Take the Ainsworth Lumber/ Weyerhaeuser partnership in Grande Prairie, for example. The first 40-hectare test block was harvested in 1996/97 after about a year of surveys and planning, with the objective of 60 to 70 per cent aspen recovery, leaving 30 to 40 per cent to avoid blow down of spruce understorey. "We took about 65 per cent of the deciduous overstorey off of this stand and we achieved 150 cubic metres per hectare recovery or about 5,600 cubic metres in total," says Williamson. "If we had waited another 80 years, we'd probably be looking at 20 to 30 cubic metres per hectare, so that's a significant difference."

Conifer consumer Weyerhaeuser stands to benefit with significant incremental coniferous growth after the spruce is released from competition. "Some of the research is showing fairly significant increases in growth in the conifer understorey," says Williamson, "in some cases, up to a 100 per cent or greater increase." A second reason for this growing interest in mixed wood management relates to Canada's evolving forest industry. Over the past 20 years, careful logging has been a high priority for governments when drafting environmental protection policy. Both companies and educational institutions have had to adapt. Foresters and contractors working in this environment are now better equipped to plan and execute complex forest management strategies. Terms such as "biodiversity" are now heard frequently and openly throughout the forest industry. "All of our contractors were interested in taking this trial on because it's new, interesting, and different," says Williamson. "They want to see if they can be innovative and provide ways to do the job better." Ainsworth focused its planning on block management. They allowed contractors to continue to use feller bunchers and skidders, but within a highly restricted harvesting pattern. 

The partners wanted to compare apples to apples when reviewing production costs, and since conventional tree length logging is the predominant harvesting approach in the area, that is what they used in the trial area. "In terms of machine productivity in this stand, we lost about 10 per cent productivity," notes Williamson. "There's an extra cost, but the stand is also very close to the mill so we're saving on transportation costs. There are lots of opportunities to make this economically viable, and in fact, we think it is now." The challenge is to balance extra planning and production costs with additional fibre recovery. That starts with choosing a suitable trial location. The first rule of selecting a potential mixed stand for this prescription is-ironically- that there are no hard and fast rules. It helps to be innovative. Typically, foresters can expect a wide variance in the ratio of deciduous to coniferous in each mixed stand. 

Even within the stand, there are thick sections where plenty of trail layout planning is required and sparse sections where the contractor can pick and choose his own path. Williamson says that their first trial stand had 1,900 conifer stems per hectare and, once they completed harvesting, there were approximately 1,450 remaining. "So we were fairly comfortable that with this kind of stocking that this would be a fully stocked stand at maturity," he says. The second trial site was not as well stocked. It had about 900 conifer stems per hectare, and they ended up with about 630 after harvesting. "Since there were fewer stems to start with, that's becoming a little more marginal," he says. "You have to be a little more concerned that it might not be fully stocked, and maybe on those types of stands you do some under planting to bring it back to full occupancy. There will still be a release effect, but is that enough to offset the loss of 300 stems? That's what has to be determined." Mixed wood management requires a great deal of cooperation between deciduous and coniferous consumers in overlapping areas. With the Ainsworth/Weyerhaeuser partnership, Ainsworth conducted the harvesting as well as pre and post survey work. 

The harvesting component of the mixed wood management program created a great deal of interest among logging contractors, who were intrigued by the innovative nature of the trial.

Weyerhaeuser is following up with growth and yield studies with a strong focus on the release effect. After a year of planning, the harvesting took only about a month to accomplish on the first trial site. They constructed three roads, 400 metres apart, on the site. The skid trails were 25 metres apart, running perpendicular to the prevailing winds. The feller buncher harvested the deciduous wood and laid it behind the machine as it proceeded down the skid trails. The operator was not allowed to travel off the trail to harvest wood. The boom and head had to be able to reach in, harvest, and pull the fibre back to the trail. The skidder then followed up and skidded the wood to roadside. Ainsworth restricted skid distances to about 200 metres. "We also tried to schedule the harvesting so that we weren't in a period when we'd be doing a lot of damage," says Williamson. "If it was really cold, the concern is that even if you just brushed up against another tree, it wouldn't bend. It would just break. 

So we tried to stay in the right kind of weather." That was temperatures above 25 to 30 degrees below zero. Discovering that machine productivity dropped about 10 per cent using this method versus conventional logging was part of the learning experience. "I think we'd have to adjust our rates for this kind of work," says Williamson, "but it wouldn't be to the point where it's not economical to do it any longer. I think there's still room to manage these kinds of stands, get them to the mill, and be competitive." Ainsworth has identified about 40,000 hectares within the 1.1 million hectare land base that have the potential for this type of harvesting treatment. Williamson says they could capture an additional 60,000 to 80,000 cubic metres as part of their annual allowable cut, "so there's a fairly significant amount of volume out there." While the results to date have been extremely encouraging, Ainsworth and Weyerhaeuser believe more study is required. 

There is a number of ecological issues that need to be addressed, explains Williams. "We're talking about wildlife and the long term productivity of these stands from a forest perspective and what sort of biodiversity are we going to have in these stands versus letting them grow as a mixed wood stand, continuing to grow with the conifer understorey eventually taking over and becoming the dominant tree species." A research program has been initiated to look at this question. There is also a bit of a political issue to be dealt with. Once the spruce reach maturity and the area is clear cut, how will the land base be managed from a silvicultural perspective- deciduous, coniferous, or as a mixed wood stand? The Alberta government is helping out in this area by developing new regeneration standards where there is not only a conifer and a deciduous standard, but also a mixed wood standard. 

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