To Prune or Not to Prune
The answer might be 20 years away

By Nels Hanson

Knot-free second growth logs may bring a substantial price premium when there isn't any more old growth to saw into knot-free lumber. If this is the case, a decision to prune may bring you a substantial return on your investment 20 or more years from now.

On the other hand, if technology develops a comparable substitute for knot-free products - or the public no longer wants it–then your only return will be a far more attractive forest that is good habitat for wildlife.

Pruning is like any other long-term decision a forest landowners must make, such as whether to plant cedar or fir; whether to let alder take over in an area or get rid of it so conifer can grow, or whether to pre-commercial thin or let nature do it. The major difference is that pruning requires more up-front investment and more labor per acre than other decisions we make.

In spite of the uncertainty, my family started pruning about 10 years ago. We prune to a height of 19 feet to have a 16-foot knot-free log at harvest. There are different ways to get to 19 feet. Some do it all in one "lift," that is, they prune the entire distance at one time. Others do the ground-level lift one year and the upper part several years later. We prune in three lifts spread over six or seven years.

The limbs are cut from the first eight feet when the trees are five to six inches in diameter at breast height. All 300 trees per acre are pruned, except conspicuous culls, simply because the stand looks so much better when it is opened up to that height.

The second lift, another six feet, is pruned about three years later, but only the 160 best growing and best-spaced trees on each acre are pruned. The third lift, another five feet, is pruned two to three years later when the diameter here is about five inches.

Handsaw preferred

We have tried most types of equipment including handsaws, pole saws, motorized saws on a telescopic pole, and clippers. We have not tried the pole with the bicycle seat. After trying them all, the handsaw with contoured wood handle was the tool of choice on all three lifts.

A conventional eight- or nine-foot lightweight aluminum extension ladder is used for the second and third lifts. A strap aluminum "M" is bolted to the top of the ladder to straddle the tree (for safety) and to hold the top of the ladder about a foot away from the tree.

About 100 trees can be pruned per day on the first eight-foot lift. About half that number can be done each day on the second and third lifts because carrying and using a ladder slows things down.

The telescopic pole motorized pruner is used on scattered trees with particularly large limbs. By definition, it is lightweight, but when extended 10 or 12 feet overhead, the definition seems absurd after you have done three or four trees.

Pruning is very hard work. It is physically demanding, and pruning must be done carefully without damage to the tree.

A person might wonder how much more harvest income would be needed to recover the investment in pruning. To answer that question, some assumptions must be made. Here are mine: • The cost to prune is about $400 per acre. • The practice must bring a compound rate of return of 7.2 percent plus inflation. • Harvest at 45 years (30 years after pruning). • The yield is 45+ thousand board feet per acre of which the bottom (pruned) logs will be 16 thousand board feet.

To recover the investment 30 years later, plus inflation and compound interest of 7.2 percent, these pruned logs must bring $3,200 more per acre than had they not been pruned. That means these logs must bring a premium of $200 per thousand over the same logs with knots.

If the volume remains the same (16 thousand board feet of knot-free logs per acre), but the premium is $140 per thousand, or $2,300 per acre, your return would be six percent compounded. If the premium is $340 per thousand, or $5,400 per acre, your compound rate of return is nine percent.

Will this investment pay off? I think so, but am not sure! Some ask: Why do it then? The same questions were asked about planting seedlings instead of natural reseeding back in the 1950s. It takes 20 years or more to find the answer. Pruning–like reforestation–is another example of why forestry does not attract the impatient.

Nels Hanson is executive director of the Washington Farm Forestry Association and owns 640 acres in Thurston and Lewis counties. He received an award from the Lewis County Chapter for his pruning activities in 1999.

This article appeared in the Northwest Woodlands magazine , Winter 2000 - Published quarterly by the World Forestry Center as a benefit of membership in the Oregon Small Woodlands Association, Washington Farm Forestry Association, Idaho Forest Owners Association and Montana Forest Owners Association.