What Methods Do Foresters Use For Harvesting Trees?

Most people have hear of terms like clearcutting or thinning, but they are only two of an array of harvest methods available to foresters. Some harvest methods, such as clearcutting, are used to promote reforestation and remove wood from the site efficiently. Others, like thinning, are used to generate cash flow and improve growing conditions by removing some of the trees, but are not reforestation methods.

The choice of method is determined by a complex evaluation of landowner objectives; site characteristics such as terrain, tree species, and regulatory constraints; and effects on fish, wildlife, and other natural resources. And harvests themselves are just a single occurrence in a decades-long series of cultivation and harvesting activities in the life cycle of a managed forest.

To greatly simplify, there are two general methods of management and harvest in Oregon known as "Even-aged Management," and "Uneven-aged Management."

Uneven-Aged Management -- As the name implies, uneven-aged silviculture involves the cultivation of trees of various ages in a stand and the periodic harvest of selected trees. Uneven-aged stands often contain mixed species as well. Trees are harvested either singly (single tree selection) or in groups (group selection) as they reach maturity.

The small gaps created by harvesting leave room for natural seeding or transplanting or nursery-grown seedlings. A common management method east of the Cascades, it is often called Selection or Selected Harvest, Selective Silviculture or Multi-aged Silviculture. It is aesthetically more pleasing than clearcutting, but seems to work better in the more extreme climate of eastern Oregon.

Even-Aged Management -- This is the most common method for regenerating Douglas Fir, the dominant species in western Oregon's commercial forests because this species grows best in nearly full sunlight. After harvest, foresters plant Douglas Fir, often mixed with other seedlings, and keep low-lying vegetation from crowding them out for a few years until they are established.

Some thinning may take place after 10 to 20 years to stimulate growth, and one or more commercial thinnings often occur between 20 and 40 years. The final harvest completes the cycle and usually occurs between 40 and 80 years when trees are 12" to 30" in diameter. This is called clearcutting because it sets the stage for reforestation and a new cycle to begin. There are variations to this cycle. The most common is Shelterwood, where a portion of trees is left to shelter the regeneration , but is often removed once the new forest is established.

SOURCE: Oregon Forest Resources Institute, Forest Fact Book.