New Compatible Estimators for Survivor Growth and Ingrowth from Remeasured Horizontal Point Samples
Forest volume growth between two measurements is often decomposed into the components of survivor growth (S), ingrowth(Z), mortality (M), and cut (C) (for example, Beers 1962 or Van Deusen et al. 1986). Net change between volumes at times 1 and 2 (V1 - V2) is then represented by the equation V,-V,=S+I-M-C. Two new compatible pairs of estimators for S and Z in this equation are presented for use with the usual estimators of V2 and V1 from permanent horizontal point samples. In addition, a new estimator for V1 (V1**) is presented, which takes advantage of the data from time 2. These estimators are evaluated along with previously existing estimators over a range of sample sizes. In all but the smallest of inventories, one of the new estimators of S (S**) will provide better estimates of survivor growth in more cases than any previously developed estimator of S.S** is shown to be compatible withV1** and the Purdue estimators of ingrowth, while empirical evidence is presented to support earlier contentions that the Purdue estimator is the best possible estimator ofingrowth from point samples. Recommendations are given based upon the presence or absence of a compatibility requirement and willingness to change the estimate of volume at time 1. For. Sci. 35(2):281-293.