Hardwood Silviculture Notes
The two-age system is designed to maintain two distinct age classes in a forest. This system is generally initiated using a deferment harvest, sometimes referred to as a shelterwood or clearcut with reserves (Figure 1). The deferment harvest retains a limited basal area of canopy trees while allowing the majority of the area to regenerate. The harvest initially creates a stand that contains scattered or small groups of older trees, typically one rotation length in age, surrounded by a regenerating age class. The canopy trees that are left are termed reserve trees. At the end of a second rotation length the stand contains a limited number of large reserve trees, two rotation lengths in age, and a larger number of trees that are one rotation length in age.
The two-age system is a viable method for managing many hardwood stands where longer-lived species are present. The system provides for vigorous regeneration and the development of average size and valued sawtimber trees and a significant component of older and larger high-value veneer and grade sawtimber trees. The system also provides for structural components that are lacking in even-aged stands. These structural components can benefit wildlife populations and provide old-growth characteristics. Like any silvicultural option, the two-age system has benefits and constraints and is not appropriate for every management objective or stand condition. The system does provide landowners and managers with options not available with other systems; however, proper implementation is required.
"SP679 Two-Age System and Deferment Harvests," The University of Tennessee Agricultural Extension Service, R12-4910-026-005-06 SP676-1.5M-6/06 06-0332, http://trace.tennessee.edu/utk_agexfores/25