We often take the wood we use to build with for granted. We don’t have to cut down trees or process the wood — we can drive to our local hardware store or lumber yard and purchase the lengths and widths we need. How does wood make it from the forest to the lumber yard or home improvement retailer? Let’s take a closer look at how we process wood, from tree to sawlog to lumber, and all the steps in between.
We’ve come a long way from the times where lumberjacks would fell trees with axes and massive crosscut saws. Today, loggers harvest wood in one of two ways. Clear-cutting removes all the trees in a specific area. While this makes economic sense, it can also be devastating to the forest’s ecosystem, so many companies are trying to move away from this type of harvesting. Trees are also harvested based upon two major end-uses; pulpwood, which is used for making paper, and sawlogs, which are used to produce the lumber found at your local lumber yard or home improvement store.
The other process uses silviculture, or the science of growing and harvesting trees sustainably. Instead of using heavy equipment to cut down every tree, a professional forester will select specific trees based upon their species, merchantable volume, and overall condition, and mark each to be dropped by a logger.
Loggers can’t process a tree into lumber while it still has its branches. That’s where the next stage — bucking — comes in. A logger with a chainsaw, and in some cases, a small remote-controlled feller/buncher machine, will move from the bottom of the tree to the top, cutting it into specific length sawlogs and removing all the branches. From there, a professional forester will sort the sawlogs by species and overall condition before forwarding them to their next destination — either directly to a sawmill, or to a concentration yard where they’ll sit until needed.
Sawmills date back to 500 B.C.E. when all the labor was manual — workers would process raw trees into lumber for building. Today, most of the work relies on massive computerized circular and bandsaw blades. Most sawmills are so busy they operate 24/7.
Sawmills start by putting each log into the head rig, which cuts the tree down into boards. Then, lumber workers edge the wood to remove any defects, trim them to square all the ends and cut them down to a uniform length. This phase is where massive logs become the 2 x 4s and other standard cuts of lumber we’re all familiar with.
While they’re cut to size, they’re not quite ready for shipment to your local lumber yard or home improvement store just yet. The wood still needs to dry before it can be suitable for use in construction.
Fresh or green wood is still full of water. Green wood isn’t suitable for most construction or building projects because it is subject to shrinkage, which can lead to cupping (U-shaped ends), crooks (a sag that you might see in an old bookcase shelf), and bowing (a board with a slight curve to the right or left). Green wood is also susceptible to mildew and mold, so it needs to undergo a drying phase first.
If you’re felling trees to use for woodworking projects, you can air-dry the wood. It takes longer than other methods, but it provides a more stable medium for construction because it doesn’t damage the wood. In a warm, dry environment, it will usually take between 45 and 60 days for the wood to dry to the point of being workable. In the lumber industry, not everyone has time to wait for their wood to air dry, so that’s where kiln drying comes in.
Kiln drying uses heated kilns to force the water out of the wood, helping it reach its equilibrium moisture content, or EMC, faster. The EMC is the point when the wood will no longer lose or absorb moisture.
Planning and grading
Once the wood is dry, the next step is planing it — ensuring each piece of lumber is smooth and meets the requested size and thickness. Now, it will look like the lumber you’re used to purchasing for your building project. Before it reaches its final destination, the producers will assign each piece a grade according to its species, quality, and moisture content.
From the forest to the lumber yard
Bringing a tree from the forest where it grows to the lumber yard so you can turn it into a woodworking project is a long and drawn-out process, but now you have a better idea of what it takes to create lumber.
This article was written by Megan Ray Nichols. If you enjoyed this article, please visit her website Schooled by Science.