VARIANCE REDUCTION IN UENOS METHOD AND CYLINDER SAMPLING FOR FOREST VOLUME ESTIMATION

Three basic techniques are proposed for reducing the variance of the s tand volume estimate provided by cylinder sampling and Ueno's method. Ueno's method is based on critical height sampling but does not requir e measurement of critical heights. Instead, a count of trees whose cri tical heights are less than randomly generated heights is used to esti mate stand volume. Cylinder sampling selects sample trees for which ra ndomly generated heights fall within cylinders formed by tree heights and point sampling plot sizes. The methods proposed here for variance reduction in cylinder sampling and Ueno's method are antithetic variat es, importance sampling, and control variates. Cylinder sampling witho ut variance reduction was the most efficient of 12 methods compared in computer simulation that used estimated measurement times. However, c ylinder sampling requires knowledge of a combined variable individual tree volume equation. Of the three variance reduction techniques appli ed to Ueno's method, antithetic variates performed best in computer si mulation.