What We've Learned About Pruning Douglas-fir

By Lynn & Linda Butts

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

In 1992 we began to see information about the advantages of pruning Douglas-fir stands and obtained a video about pruning produced by the Canadian Ministry of Forests. Besides showing ways to prune, the video discussed the advantages of pruning: increased strength and density, and the desirable appearance of clear wood for solid wood products and veneer. We also attended seminars that demonstrated equipment and techniques for proper pruning. The thinking is that knot-free wood will bring premium prices in the future, although like most things in life, there are no guarantees.

In 1993 we began pruning a 15-year-old stand of Douglas-fir. We discovered we should have started pruning earlier in this stand because the limbs were large and many of the bottom whorls were dead, which made them very hard to cut. Recommended pruning height is to leave 50 percent of the live crown, so we could prune to 10 feet without affecting the trees' growth. We tried several kinds of loppers and found that a compound bypass style worked best for us. Linda likes the New Zealand style because they work great for the tough dead branches, but they are heavy to carry.

Trees are pruned in "lifts," which is the distance pruned up a tree at one time. The first lift can be any height, provided that not more than 50 percent of the live crown is removed. Additional lifts are made to maintain 50 percent live crown on the tree until the final pruning height is reached. The final pruning height will vary depending on what length of clear wood log you want to market. The limb should be removed just outside the branch collar without damaging the collar and without leaving a branch stub. The growth the tree puts on after healing over the stub will be clear wood. The smaller the diameter of the tree when pruned, the smaller the knotty core will be, and more inches of clear wood will be on the tree at final harvest.

Most information recommends using loppers for the first lift, although some people use handsaws. For the second lift and higher, polesaws and types of ladders can be used. There have been a variety of ways developed to prune higher in the tree including power equipment that spirals up the tree pruning off the limbs as it goes.

In New Zealand, Radiata pine is pruned using loppers and various ladder systems. The pruning there is driven by market demand and done according to specifications set by the mills. Teams of young men that are specially trained do the pruning. In Chile we saw men using handsaws and special footgear for climbing the trees. Some simply climbed the tree and sawed off limbs on their way down. No safety gear was used! Lynn imported a ladder and step combination from New Zealand so he could prune higher than can be reached with a polesaw.

In the past six years, we have pruned the first stand of 22 acres up to 20 feet and begun pruning a 30-acre stand when it was nine years old. For the first lift, we feel it is an advantage to prune every tree, as this gives better access into the stand and reduces fire hazard by raising the fire ladder. It also makes it easier to identify the better trees for future pruning lifts. After pruning two lifts on every tree in the first stand, Lynn has come to the conclusion that there is no advantage to pruning every tree past the first lift. He feels his time and effort is better spent concentrating on the best trees to prune and save for final harvest.

We believe that our efforts in pruning will be worthwhile economically. It is important to keep good records of pruning, with details as to how and when it was done, including age and size of trees and equipment used. Photographs are also a good idea. It might also help to develop a good relationship with your local log buyer so he knows you are pruning. Invite him for a tour, and when it comes time to harvest, he might remember you, and your clear wood will bring a premium.

Lynn and Linda Butts are family forest owners who live in Clackamas County, Ore., and own a 145-acre tree farm in Linn County. They were Western Region Outstanding Tree Farmers in 1998. Lynn serves as second vice president of the Oregon Small Woodlands Association and Linda is an associate editor of the Clackamas County Forest Tree Leader newsletter.