Allowable Cut and Allowable Cut Effect

 
Joseph Roise
North Carolina State University

 
The Allowable Cut is the volume of timber that can be harvested each year under a planned harvest schedule and is determined using a variety of techniques of harvest scheduling. Long term sustained yield (LTSY) is the allowable annual cut (AAC) for a regulated forest. LTSY represents the maximum physical production of wood that can be sustained in perpetuity and is perceived as an upper limit on sustainable harvest level.

In the US Forest Service the term Allowable Sales Quantity (ASQ) is often used instead of allowable cut. The difference is that ASQ is what is put up for sale, but not necessarily purchased and/or cut. In a harvest schedule, the allowable cut can increase or decrease from year to year, but in some cases policy constraints such as “Non-declining Yield” can lead to a constant value for AAC, after the first few periods of adjustment.

The Allowable Cut Effect (ACE) posits that there can be changes in the AAC caused by changes in silviculture and management practices, or forest area, when managing under harvest flow constraints. Simple examples of ACE are that by increasing forest area, or implementing silviculture that increase forest growth and yield, owners also increase the LTSY of the forest.

It is not controversial that management practices influence AAC. When introduced in the 1970s, the ACE was controversial, when forest analysts suggested that you could increase AAC by cutting more slow growing mature trees and replacing them with faster growing young trees. This did not change the LTSY, but did change the shorter term AAC, which was constrained at the time by estimates of forest growth. Environmental groups and even many foresters challenged the wisdom of liquidating old stands faster, despite the mathematics of the ACE. 

This debate has subsided as fewer old growth stands are harvested and converted, but the concept remains part of the technical tools and debate.  For instance, the same principle may apply when fertilization is applied—the faster growth rate may allow an increase in present harvest levels due to faster growth and greater yields in the future.