Comparison of Nearest Neighbor Methods for Estimating Basal Area and Stems per Hectare Using Aerial Auxiliary Variables

Simulations were used to compare variable-space nearest neighbor methods for imputing stems per ha and basal area per ha (ground measured) for complex stands (many species and sizes) of southeastern British Columbia, Canada. Species composition and other characteristics obtained for every stand by interpreting aerial photography were used as auxiliary variables. The simulations included three distance metrics (squared Euclidean distance, most similar neighbor, and absolute distance), three intensities of stands with full informa- tion (20%, 50%, and 80%), two sets of aerial variables (mixed versus moderately high correlations with ground variables), and three averaging methods (nearest neighbor, average of three nearest neighbors, and distance weighted average of three nearest neighbors weighted). Increasing the number of stands with full information to 50% from 20% resulted in increased accuracy, with no noticeable improvement with a further increase to 80%. Of the three distance metrics, the most similar neighbor measure gave good results in imputing stems per ha and basal area per ha, particularly when there was a mixture of correlations, high and moderate, between the auxiliary (aerial) variables, and the ground variables. No large gain was noted in using the average of three neighbors rather than a single neighbor. FOR .S CI. 51(2):109-119.