Effects of competitor spacing in a new class of individual-tree indices of competition: semi-distance-independent indices computed for Bitterlich versus fixed-area plots

Ottawa

2008

S. 890-898

Artikel aus einer ZeitschriftUnselbständiges Werk

200145584

Comparisons of effects of competitor spacing in semi-distance-independent indices of competition show that some combinations of competition variables and sample plot designs can generale CIs ihal are very similar to the consensus of distance-dependent indices, e.g., basal area per unit area or TAR estimated from Bitterlich samples (compare Figs. 6 and 7 with Figs. 8 and 9). However, other combinations of competition variables and plot design produce anomalous distance and (or) size effects. The results show that modellers of growth and designers of inventory plot configuation should consider the interaction of these two parts of their system if they are intended to be used for stand growth analysis or inventory projection. Comparisons between these two classes of CIs suggest that optimum plot sizes for estimating semi-distance-independent CIs are smaller than plot sizes commonly used for estimating stand volume. In particular, the similarities of basal area distance effects, as measured by Bitterlich samples, to the effects implicit in the collection of distance-dependent indices suggest that growth models using basal area related competition variables (i.e., as semi-distance-independent indices) are able to capture the effects of tree spacing without the necessity of stem mapping. Thus, we believe that the results of this study provide the theoretical basis behind the findings of Biging and Dobbertin (1995) and Windhager (1999). However, more specific and concerted analyses remain to be done to answer the question of whether variation between actual space occupancy and that assumed to be captured by sophisticated measures of crowns and spacing in some of the distance-dependent measures explain more or less variation in actual prediction of tree increment than does the point variation in semi-distance-independent basal area measured from Bitterlich samples.