Reproducibility and Reliability: How To Define the Population of Trees That Represent Site Quality For Longleaf Pine PlantationsThis article is part of a larger document. View the larger document here.
We compared 13 definitions for the subpopulation of “site trees.” Each subpopulation was defined (1) once at base age or at each measurement; (2) by crown class, diameter, or height; and (3) by the number of trees per acre. These subpopulations were applied to base ages of 25 and 50. For base age 25, the subpopulations defined at base age were superior to those defined at each measurement. The subpopulations defined by dominant and codominant trees were slightly superior to the subpopulations defined by the 40 tallest or thickest trees per acre. Generally, subpopulations defined by diameter were superior to subpopulations defined by height, and the subpopulations that included more trees were superior to those that included fewer. For base age 50, there was very little or no benefit from defining the subpopulations at base age. Among the subpopulations defined at each measurement, the one defined as dominant and codominant trees was superior. We selected this subpopulation for our site index modeling work. The results are largely explained by the stability of tree rankings within a plot over time. Ranking with respect to height is much less stable than ranking by diameter. Crown class was unexpectedly stable from measurement to measurement.