There are two basic approaches to harvesting timber. The first, commercial clear-cutting, focuses primarily on economic gain. In this approach, loggers remove all trees in a forested area, usually down to a small diameter, such as 6 inches (15 cm). The effects of clear-cutting can be devastating. When the harvest is complete, a once-beautiful forest can resemble a wasteland. More important, clear-cutting doesn't allow for sustainable forestry, which balances the perpetual growing and harvesting of trees with environmental protection and conservation.
The second approach to harvesting timber is based on silviculture -- the science of growing and harvesting trees for sustained yield. Silviculturists rely on several methods to harvest timber. One important method is shelterwood cutting, which uses partial cuttings over time to remove an entire forest, but gradually. In this way, desirable tree species naturally regenerate and grow into the new forest. Shelterwood cutting involves a series of two to four harvests occurring over a period of 10 to 20 years.
Foresters must analyze timberland carefully to determine which method of silviculture harvesting to use. Indeed, proper forest management involves balancing the economics of the harvest with the biology and ecology of the forest. Once these strategic issues are determined, foresters can survey timberlands to locate and estimate the volumes and grades of standing timber that meet their requirements. This process is called cruising.
National Geographic/Getty Images
Next comes felling, or cutting down trees using a chain saw. To fell a tree, a worker makes four cuts: a top, bottom, back and felling cut. If you saw the tree after all those cuts but right before it fell -- not that we're suggesting that! -- it would look like it had two triangle-shaped bites taken out of it on either side. The goal is to leave a sufficient hinge of wood between the bottom cut and felling cut. This reduces tree kickback and provides greater control over where the tree will fall. When a team of loggers is working together, the tree faller usually shouts that "Timber!" warning that you're familiar with to alert fellow workers that a tree is about to fall.
Once a tree is on the ground, loggers remove its limbs and cut it into logs, a process known as bucking. Bucking involves making cross-sectional cuts, from the butt of the tree to the top. Next comes skidding, or moving logs from the forest to the landing area. Loggers skid timber by winching several logs to a tractor and dragging them through the forest along designated trails. Preplanned skid trails protect the forest floor by limiting soil compaction, which increases the soil's ability to grow trees in the future.
According to the U.S. Department of Labor, logging is the most dangerous occupation. A full-time logger has a better than 1 in 1,000 chance of getting killed on the job [source: Shaffer]!
At the landing area, workers grade and sort logs by species. Then they load the logs onto trucks, which deliver the timber to its final destination. Pulp mills receive lower-grade logs, while veneer producers receive higher-grade logs. The rest of the timber either goes directly to sawmills or to concentration yards. Concentration yards sell and market logs to sawmills based on the mill's needs. Many sawmills specialize in a certain type of log and rely on concentration yards to collect and organize timber to meet their specifications.
Finally, the timber is ready for processing. In the next section, we'll examine how a sawmill transforms a single log into the lumber stacked in your local lumberyard or home improvement store.