Statistics? We Don’t Need No Stinking Statistics! or Using Stem Maps to Compare Cruising Methods For Allowable Cut Calculations in Uneven-Aged Longleaf Pine

Abstract

This study examines sampling methods to determine current stocking of uneven-aged longleaf pine stands for determining allowable cut. Heretofore it has often been assumed that stands smaller than 100 acres should receive a 100 percent inventory to accurately determine current stocking. The variability inherent in uneven-aged stands generally, and in longleaf pine particularly, compels the forester to take an excessive number of samples to achieve statistical confidence in the estimate. A 100 percent inventory is often deemed the simplest, if not the easiest, solution to the quandary. The expense of a full inventory is a deterrent to applying uneven-aged management to tracts under 100 acres. Tracts under 100 acres comprise a large portion of the current land ownership across the original longleaf pine range, and will be a critical component of any meaningful restoration effort. Estimates from different sampling intensities and techniques were compared to known populations. Two 40-acre study sites were stem-mapped pinpointing the location of each tree >3.1” dbh. Samples were constructed based on tree coordinates and tree dbh using several traditional sampling methods. A simple method of prescribing target stand structure called Whole Stand Regulation (WSR) was used to determine the target number of tree per acre by dbh class. This method was applied to estimated stocking and results compared to the residual structure of the stand based on a 100% inventory. An acceptable error of <+6% of tree count in each of three size categories was achieved through different combinations of methods. A 10BAF prism sample in combination with a 1/20 or 1/10 acre plot sample provided the data necessary to incorporate adjustments using point-double sampling to yield estimates well within the acceptable limits. Based on these results, foresters should be confident in pursuing uneven-aged management without relying on costly 100% inventories to determine allowable cut.