Using TIPSY to Evaluate Windthrow Effects on Regeneration in Variable Retention Harvests

The Table Interpolation Program for Stand Yields (tipsy) enables forest managers and timber supply analysts to explore the impacts of variable retention. tipsy variable retention adjustment factors (vrafs) are calculated based on the level and pattern of both group and dispersed tree retention using four primary variables from the retained stand: percent crown cover, average group or crown size, initial edge length (perimeter), and top height. Windthrow losses in the years shortly after harvest can now be estimated using two methods; empirical regression equations that predict windthrow effects, or specifying expected windthrow losses for a given location. vrafs reduce post-harvest regenerated yields on a per-hectare basis over the entire cutblock as a function of the area occupied by retained trees. Windthrow losses will reduce the crown cover retained and therefore increase the growing space and future yields for the regeneration.