n Southern African Forestry Journal - Forecasting volume and economic gains from intensive plantation management using different response curves : management paper




Proponents of intensive plantation management do not all use the same type of response curves when predicting future volume gains. As a result, some believe that continuously increasing the intensity of management will increase landowner profits and reduce the unit cost of wood production (i.e. all silvicultural costs per ha/merchantable cubic metres per ha at harvest). A few believe there is no upper limit to stand productivity while others use response curves that follow the law of diminishing returns. Using loblolly pine (<I>Pinus taeda</I>) data from Georgia as a point of reference, we developed four hypothetical production models (where yield is a function of silvicultural effort). The models that produced apparently unrealistic results were (1) an exponential curve and (2) a linear curve where the costs of growing a cubic metre of merchantable wood (at time of harvest) was inversely related to the discounted cost of intensive silviculture. Although increasing silvicultural effort will often result in more merchantable volume at harvest, the extra wood volume might not be enough to prevent a reduction in net present value of the stand. Harvesting intensively managed loblolly pine stands at age 15 years might not prove economical for a private, non-industrial landowner in the USA if the costs of establishment are too high or if no local mills will purchase logs that contain a high percentage of juvenile wood.


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