Precision of Density Estimates from Fixed-Radius Plots Compared to N-Tree Distance Sampling

We computed and compared the statistical properties of the estimators for the number of trees/ha (density) for fixed-radius plot and n-tree distance sampling. In forests with random spatial patterns, n-tree distance sampling density estimators are at least as precise as those of plot sampling if the fixed-radius plot size is less than the ratio of (n - 2) and the expected density, where n is the number of trees included at an n-tree location. A similar result holds for the clustered forest, where the ratio is multiplied by a factor involving a constant of heterogeneity. If the expected number of trees per plot and the plot sizes are the same for both the random and clustered spatial patterns, the variance of the plot sampling density estimator for the clustered pattern will always be greater than for that of the random spatial pattern.