Quantifying the opportunity cost of extended rotation forestry with cohort yield metrics in Minnesota

Recent questions of the habitat quality and ecological benefits provided by older forests have led to the concept of extended rotation forestry. Consideration of this approach has increased in forest planning efforts in Minnesota, with some planning horizons carrying portions of forests well beyond typical rotation ages. These longer rotations often exceed stand ages found within the calibration data of most local yield models, creating a need for yield projections that better describe the development of older stands. This study modified an existing system of linked yield equations for 14 forest types to more accurately represent the entire life of a single cohort. New model parameters were added to better describe basal area development (including cohort breakup) and subsequent volume yield. In addition, a mortality yield model was proposed that quantifies the effect of stand aging and background mortality on volume yield. Those tasked with estimating yield (or yield loss) from extended rotations can now obtain more realistic projections for older cohorts than those given by typical yield models. Tradeoff analyses during forest planning and policy efforts will especially benefit from these more realistic estimates of yield and/or mortality loss.