Application of Height-Based and Diameter-Based Relative Spacing for Estimation of Stand Basal Area

Relative spacing (RS) has traditionally been defined as the ratio of the mean intertree distance to the average height of dominant trees. In this study, we evaluated two approaches for estimation of stand basal area: a stand basal area-RS model and a diameter-based relative spacing (RSD) measure. The equation form of RSD is the same as that of RS with the exception that average dominant tree height was replaced by quadratic mean diameter. In addition, the implied maximum stand basal areas developed from RSD and from Reineke's self-thinning rule were compared. Data used for analyses were obtained from a loblolly pine spacing trial, whose planting density ranged from 747 to 6,727 trees/ha. The results indicated that RS performed well for prediction of stand basal area. The stand basal area-RS model linked vertical and horizontal stand variables and provided a simple and reliable way to estimate stand stocking. RSD proved consistent with Nilson's sparsity index on projection of a maximum size-density relationship line. For estimation of maximum stand basal area, RSD largely eliminated the undesirable property of Reineke's self-thinning rule, which overestimated the maximum stand basal area when stands were young.