The use of unusually small harvesting machines, including a farm-size rubber-tired tractor, are key players in what may be the largest Tthinning operation of its kind ever tried in Canada. This research and development project for Avenor Woodlands Northwest is taking place on licensed holdings within 150 km of the company's Thunder Bay mills. 

Since May, 1996, Avenor has thinned and partially harvested approx- irnately 1,000 hectares of jackpine, poplar, birch and spruce at the site. 'This may be the largest thinning operation in non-spaced stands in Canada," says Avenor's superintendent of thinning and spacing, Phil Keenan. 

The region, logged 25 to 45 years ago, has an average of 4,000 stems per hectare today in the thinning blocks - double the number that would have been seeded or transplanted. Keenan says, "Right now it will support 4,000 stems, but with normal forestry dynamics you're only going to have 800 stems per hectare by the time these stands are 70 years old." 

By thinning, however, Avenor hopes to do a full harvest in 25 or 30 years. It may speed up the whole cycle with a possible second thinning in 10 to 15 years. "We're trying to take the wood out now that would normally die over an extended time, and make some use of it as chips. The remaining trees grow faster, with more water, more light and more nutrients. At the end of the rotation, they should be straighter, healthier and larger, so we'll have more fibre per hectare and our operating costs then will be cheaper." 

That's the idea, anyway. It will take a few years for the company to determine whether the benefits outweigh the costs. "It isn't a neat package yet, but we're at least half-way there," says Keenan. Ideally, the thinning operation will pay for itself, up front, by yielding a supply of chips for pulp mills. 

Harvesting and forwarding machines employed include a tiny, 12,000-lb. rubber tire Rocan-T harvester (see sidebar) and a Rottne-G forwarder, both supplied by Rocan Forestry Services, of Dieppe, New Brunswick. 

Despite their small size, Keenan says the machines are standing up in the application, without undo site disturbance and with all expected in terms of reasonable economic efficiency. 

"We can use those machines to get at wood you normally wouldn't get. We're able to thin along highways, go down to the water, go into moose aquatic feeding sites and work beside nesting sites for eagles or osprey." 

Rubber tires were chosen over track machines for site disturbance considerations, slays Keenan. "Because you're leaving trees to grow, you don't want to bruise their root systems. Tracks tend to do that. They crush some of the small roots, and that can be an infection point for diseases. With rubber, we have very, very low incidence of disturbance." 

In a thinning block, Avenor's two contractors open a series of parallel rows only 3.5 to 4 in wide and up to 500 in deep, starting from an existing roadside. Rows are spaced at 25 in. 

The contractors each use two harvesters and one forwarder. Reaching in up to four in from a row, with a 360' pan head on a telescoping boom, a skilled operator can selectively thin nearly half a hectare per shift. A forwarder can handle up to 200 stems per load, enabling it to keep up with two harvesters. 

About 1,600 trees per hectare are left and about 1,000 harvested, hauled to road- side by the forwarders in delimbed 16' lengths for chipping. Limbs are used as a working mat as the harvesters proceed, to reduce site disturbance. 

Cambrian Ridge Silviculture of Thunder Bay has one of the thinning contracts. Manager Rob Storkson says the light, rubber-tired equipment took some adjustment after years of operating 50,000-lb. feller-bunchers and 20,000-lb. skidders. 

"With these machines, we aren't creating ground disturbance or damaging standing timber or roots. When we're done, we want it to look like a park." 

Operators need training and time to become proficient at this selective harvesting. Initially, Storkson recalls, only 85 trees were cut on the first shift. Operators now routinely harvest 800 per shift. Avenor required operators to attend and pass a two-week course on silviculture. Rocan Forestry Service provided four weeks of training on mechanics and operating. 

Because the wood is so much smaller than anything else Avenor handles, the company at our visit was still searching for the most efficient and economic method of debarking and chipping at roadside.