Variable retention adjustment factors (VRAFs) incorporated in the Table Interpolation Program for Stand Yields (TIPSY version 3.2) enable forest managers and timber supply analysts to explore the impacts of the variable retention approach to harvesting on future harvest yields. VRAFs are based on the level and pattern of both group and dispersed retention. The VRAF model uses three primary variables from the retained stand: percent crown cover, edge length (perimeter), and top height. The system also includes subordinate models to predict edge length and retained crown cover from other retention measures such as basal area.
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Updated April 18, 2007