Incorporating Regeneration Effort as a Decision Variable in Tactical Harvest Scheduling Kevin Boston, John Sessions, Robin Rose, and Will Hoskins A variable green-up period is incorporated into a tactical harvest scheduling model to allow for the regeneration policy to be included as a decision variable. The benefit of this formulation was demonstrated by solving a 91-logging unit forest plan under four different green-up policies. The first three policies used fixed green-up periods of 2, 3, and 4 years. The fourth policy uses a variable green-up period where the model selects the regeneration effort that determines the green-up period stand by stand. This policy allows each harvested stand to choose among a 2-, 3-, or 4-year green-up period. The variable green-up period resulted in a slight improvement in the net present value because its total was approximately $3,000 or $1.11/ac higher for the total planning area, not just the harvested acres when compared with the best solutions when 4-, 3-, and 2-year fixed green-up periods were used. The variable green-up constraint adds a level of complexity to the spatial harvest scheduling problem that is easily incorporated into a variety of heuristic procedures because they do not require that all combinations of harvest units be specified before solving the problem. The results cannot be generalized to other forests because the spatial arrangement of the stands is a major component in the value determination. However, using the methodology presented, forest managers can evaluate their own alternatives that may improve the returns from managing their resources. Keywords: mathematical programming, green-up constraints I n California, Oregon, and Washington, the forest practice rules include regulations that limit the ability to harvest adjacent logging units until the regenerated trees reach a minimum height. Additionally, these limits are often contained in various voluntary certification schemes such as Sustainable Forestry Initia- tive (SFI) and Forest Stewardship Council (FSC) schemes (FSC 2005, SFI 2005). This exclusion time is known as the green-up period. Boston and Bettinger (2006) describe the various green-up requirements found in the forest practices rules in three western states: California, Oregon, and Washington. The basis for early regulations was to insure a seed source from adjacent stands, but more recently the rationales have been for aesthetic, wildlife habitat, soil, and water quality concerns. For state and private timberlands in Oregon, the requirement is that the regenerated stand must be “free- to-grow.” In Oregon, “free-to-grow” is defined as when the average height of the regenerated stand is 4 ft (OSR 527.740). The time to reach a minimum height is a function of a number of factors includ- ing inherent productivity of the site, seedling quality, seedling size, and control of competing vegetation. The length of the green-up period must be included in the spatial harvest plan to insure that a feasible harvest schedule is produced. In western Oregon, the green-up time is considered to be 4 –5 years. However, increased management intensity in the Douglas-fir region of western Oregon may be able to reduce the green-up period to 2 or 3 years (Rose and Ketchum 2002, 2003; Rose et al. 2006). Shortening the length of time for stands to reach the “free-to- grow” stage can potentially permit earlier harvest of adjacent units. Thus, it may provide an immediate return to the landowner to be added to the benefits generated from accelerated early stand growth. The effect on discounted revenue on being able to harvest adjacent stands earlier depends on their value growth rate. For example, if it is possible to harvest an existing adjacent stand of equal area worth $20,000/ac (excluding regeneration costs) 2 years earlier by short- ening the green-up period from 5 to 3 years, the change in dis- counted revenue is $1,847/ac less the value of 2 years value growth for the existing adjacent stand (6.0% discount rate). If the value growth of the adjacent stand was 3.0%/year, the net change in discounted revenue would be $1,024/ac. However, if the value growth of the adjacent stand was equal to the discount rate, the 2-year delay would result in no change in the discounted net revenue. The objective of this article is to introduce a new formulation that incorporates variable-length green-up constraints that allows the model to select different regeneration intensities for meeting the adjacency requirements and its influence on net present value (NPV) formulation for the spatial harvest scheduling problem. In this problem, the green-up time is controlled by determining the regeneration intensity to apply to recently harvested stands. Thus, a greater intensity of regeneration effort will result in a shorter green-up period. The study compares the NPV of various fixed green-up periods with this variable green-up problem. Others have compared the economic and ecological outcomes from various fixed green-up periods and opening size and they have shown that smaller maximum opening sized units and longer periods can have a signif- icant impact on the returns from a forest with a reduction in sus- tainable harvest levels between 2 and 29% when 10- to 30-year green-up periods are used with maximum opening size ranging be- tween 20, 40, and 80 ha (49, 98, and 198 ac; Daust and Nelson 1993). Boston and Bettinger (2001) showed between a $10.00 and Received January 4, 2008; accepted April 4, 2008. Kevin Boston (kevin.boston@oregonstate.edu) and John Sessions (john.sessions@oregonstate.edu), Department of Forest Engineering, and Robin Rose (robin.rose@oregonstate.edu), Department of Forest Science, Oregon State University Corvallis, OR 97331.Will Hoskins (wphoskins@gmail.com), Longview Fiber, Longview, Washington. Copyright © 2009 by the Society of American Foresters. WEST. J. 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