A Forester's Perspective

By Jesper Nielsen

NACFOR recently prescribed juvenile spacing and pruning treatments on two cutblocks inherited from the previous tenure holders.

One of the blocks was logged in 1987, the other in 1989. Both blocks had already been declared “Free to Grow” prior to NACFOR inheriting them, meaning the previous licensees had met all of their legal silviculture obligations. This means that the blocks had been replanted and treated up to a point where a sufficient number of stems were deemed to have reached a sufficient height above the competing vegetation.

The silviculture programs NACFOR undertook on these blocks are considered to be incremental to licensee obligations and are therefore labeled “incremental silviculture.” Such programs are funded by a special provincial program, the Forestry Investment Account, or FIA.

For anyone not familiar with the term juvenile spacing, it’s really a simple concept that operates on exactly the same principle as weeding your garden. You reduce the amount of vegetative competition in order to get increased yield and value from your most desired product. Pruning is a similarly basic concept. You trim the lowermost branches from the tree in order to derive two primary effects.

The first is to allow the tree to put more energy into the higher value parts of the stem and less into branches no longer supplying much photosynthetic boost. The other intended benefit is that by cutting the lower branches off, that part of the trunk becomes knot free from that point forward. This allows the tree to produce a higher percentage of clear bole, increasing its future value.

Another benefit of spacing and pruning is that to our manicure-addicted, 21st century eyes, both practices look great. Possibly partly because spacing and pruning are so aesthetically pleasing, B.C.’s forest industry has endured significant public criticism over the years for not engaging in more of these types of incremental silviculture practices. Obviously, this criticism is not justified on aesthetic grounds. But is it justified on the grounds that the industry is not investing sufficiently to get optimum future value from its forests? As seems to be the case with so many things forestry related, the answer is complicated and site specific.

I think most foresters would agree on one thing with respect to the debate on incremental silviculture; the nature of the current tenure and appraisal systems leaves forest companies with little incentive to practice it. Aside from the limited FIA funding available to licensees, everything in the current system works to encourage companies to get trees only to free growing height (usually somewhere between 4 and 6 meters), after which they are obligated to do nothing more.

Our current forest minister recognizes that this is a problem and has promised to change this part of industry culture. One of the arguments in favour of community forestry is that it encourages incremental silviculture without having to introduce a mountain of new legislation or artificial incentives. The incentive is built in because the community has an inherent interest in passing a desirable legacy on to its children and grandchildren.

The fundamental questions are still left unanswered, however. Are the benefits of incremental silviculture really worth the investment? Is enough value gained from spacing and pruning treatments to pay for the investment costs? There are certainly cases where good arguments can be made that the investment is not worthwhile. Studies done on pine spacing projects in the northern interior strongly suggested that the benefits were insufficient to justify the costs. In general, researchers agree that large investments in incremental silviculture on poor growing sites are unlikely to generate positive returns.

There is also a school of thought that not only might juvenile spacing programs not increase long term yields, in some cases they can reduce it.

This argument is particularly compelling in the Arrow Lakes valley, where Armillaria root rot is endemic in so many of our stands. Spacing in juvenile stands possibly infected with root rot raises two fears. The first is that reducing the number of juvenile stems leaves too few stems behind to buffer against root rot induced mortality. The second fear is that cutting causes the root rot fungus to flush, hastening mortality in the remaining stems. There is some credibility to these arguments but too often, they have become a convenient reason to do nothing. More research needs to be done. And where the presence of root rot is deemed to be low or non-existent, spacing trials should be considered.

NACFOR chose two blocks for its spacing and pruning projects that are believed to have a low risk to return ratio. Both stands are located on rich growing sites. Only minor evidence of root rot was noted in both blocks. And both stands were densely packed with vigourous stems of preferred species with good potential to increase their incremental value.

The total cost of spacing and pruning treatments is a little more than two thousand dollars per hectare. Roughly calculated, the following examples indicate what is required for these investment dollars to pay off at the time of harvest. Out of 2000 remaining stems per hectare, two dozen Douglas-fir trees would need to increase from sawlog to building log value. Or twenty cedar trees would need to increase from sawlog to pole quality. Those seem like better odds than you can get on Wall Street these days.

Applied on the right sites, incremental silviculture is worth a shot.