Performance assessment of two plotless sampling methods for density estimation applied to some Alpine forests of northeastern Italy

In this study, we tested two plotless sampling methods, the ordered distancemethod and point-centred quarter method, to estimate the tree density andbasal area in some managed Alpine forests in northeastern Italy. We selectednine independent forest stands, classified according to the spatial distributionpatterns of trees (cluster, random, regular). A plotless sampling survey wassimulated within the selected stands and the tree density and basal area wereestimated by applying both the ordered distance method and point-centredquarter method. We compared the estimates, in terms of accuracy and precision, between the two methods and against estimates obtained from a simulated survey based on a plot-based sampling method. The point-centred quarter method outperformed the ordered distance method in terms of both accuracy and precision, showing higher robustness towards the bias related to nonrandom spatial patterns. However, both the plotless methods we tested canprovide unbiased accuracy of estimates which, in addition, do not differ fromestimates of plot-based sampling. The satisfactory results are encouraging forfurther tests over other Italian Alpine as well as Apennine forests. If confirmed, the plotless sampling method, especially the point-centred quartermethod, could represent an effective alternative whenever plot-based sampling is deemed redundant, or expensive.