Jim Hilton pens a column on forestry each week for Black Press Media.

Jim Hilton pens a column on forestry each week for Black Press Media.

FOREST INK: Black cottonwood has many good qualities

There are three native poplar species in this province. Trembling (Quaking) Aspen is probably the most recognized with Black Cottonwood being the second most common (in central and coastal B.C. and the Western United States). The third species is the Balsam Poplar (also referred to as Cottonwood) which is the most common in the country from the Pacific to the Atlantic throughout central Canada. The Balsam part of the name causes the most confusion since there is also a Balsam fir which is a coniferous tree.

While poplar wood does not have the mechanical strength of spruce, pine or fir it is often dismissed as a useful lumber product. We frequently hear comments that Cottonwood is a “junk” wood. I for one have found the Black Cottonwood a very useful wood which I processed on my portable sawmill. I made some very fine looking display tables which were easy to sand and stain.

According to a Woodworking article, all woods have a place and a value and even within a given species, that value can change significantly. “Cottonwood has been used for many things through the years including; shelving, framing, paneling, sub floors, crates, pallets, lowboy decks, saddles, and caskets. And the higher quality cottonwood has been used in turning.

You can surf the web at any time and find fine art and bowls that have been created from cottonwood burl, and burl cluster. Cottonwood is frequently stained to mimic other woods including Cherry and Walnut,” noted the article.

A friend mentioned to me that he had heard that cottonwood had a very good insulating quality. After a quick search about wood R-values I found the following information. Authors Baca, Waugh and Bottger from the University of San Francisco discussed the topic in the report, Thermal Properties of Poplar Bark.

“The poplar bark had a higher R-value (3.7) than expected and was significantly higher than the poplar wood itself and is higher than most wood. While it is still low compared to polystyrene it was very close to the R-value of a Fiberglas Batt. Based on this data Poplar bark could be used as a substitute for or assist fibreglass insulation. However, the poplar bark’s high R-value was initially very perplexing because it had a relatively high density. The authors decided to compare the woods with their densities to see if there is a relation between how dense a material is and how well it can retain heat.”

The fact that poplar bark does not seem to follow this relationship shows us that it has both a high R-value and density, which could be a unique strength of this specific material.

“It can reduce heat conduction as well as retain much of its heat due to its density. When poplar bark was examined we found that the R-value was quite high at about 3.7, high for a material with such a high density. With both a high density and high R-value this material shows much promise as an insulation material as well as regular house siding.”

All three poplar species are also important from a biodiversity point of view as they provide shelter and food for many species of animals and insects.

Read more: FOREST INK: More common sense needed on cull pile use

Read more: OPINION: Conserving forest, grassland and wetland ecosystems in B.C. has global impact


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