Evaluation of 3-P sampling as a midcycle measurement of CFI (Ames Plantation)

The objective of this study was to evaluate 3-P sampling as a midcycle volume estimate of CFI. A two-stage 3-P sampling technique was established for forest lands controlled by The University of Tennessee at Ames Plantation whereby the present fixed area plot CFI system was modified to include a midcycle volume and growth estimate based on 3-P sampling. The two-stage 3-P sampling technique was compared with the present CFI system by evaluating the precision and cost of each method. Using 3-P sampling with volume as a predictor and the same tree volume estimating procedures, 120 trees were selected for remeasurement versus the 2,395 trees required by the present CFI method. The pulpwood volume per acre estimated by 3-P sampling was within 1.11% of that obtained by the present CFI system. Three-P sampling estimated 225.71 cubic feet per acre while 228.23 cubic feet per acre was estimated by CFI. Sawtimber volume per acre estimated by 3-P sampling was within 0.56% of that obtained by the present CFI method. Three-P sampling estimated 4186.90 board feet per acre while 4210.39 board feet per acre was estimated by CFI. The relative standard errors for the 3-P volume per acre were 6.78% for pulpwood and 13.53% for sawtimber; relative standard errors for the CFI volume per acre were 6.91% for pulpwood and 7.67% for sawtimber. Modification of the present CFI system, by adding a basal area factor prism sample (during the first stage sample) at every plot center for measuring all trees one inch in diameter and larger, was recommended to accommodate 3-P sampling for midcycle volume and growth estimation.