Konkurrenzdruck und Zuwachs von Pinus radiata

Zusammenfassung

Die Abhängigkeitsbeziehung zwischen drei Konkurrenzvariablen und dem Volumenzuwachs vonP. radiata wurde untersucht, nämlichProdan-Ehrlenspiels n-Baum-Stichprobe (Bantre _i), eine Abwandlung vonSpurrs Modifikation der Winkelzählprobe (bangtree _i) undKennels Abstandsvariable (distree _i). Die Ergebnisse waren folgende:

• 1. In den undurchforsteten A-Flächen ergabbangtree _i die höchste Regressionsquadratsumme, in den stark durchforsteten C-Flächen dagegendistree _i.

• 2. Die Regressionsquadratsumme ist vom Wert des Index i abhängig.

• 3. Für dieselbe Baumhöhe und denselben Wert der Konkurrenzvariablenbangtree ₄ ist der Zuwachs in stark durchforsteten Beständen größer als in schwach durchforsteten.

Summary

In this study, the efficiency of three variables, to express competition amongst trees within biogroups ofP. radiata, was investigated. The variablebantree _n was defined as the basal area per hectare of the n-nearest trees. The variablebangtree _n is a modification ofSpurrs angle summation measure and expresses also the basal area per hectare of the n-trees which surround a study tree.distree _n was defined as the distance between a study tree and the n-nearest tree. The study was conducted in unthinned A-plots, in B-plots exposed to medium thinning and in heavily thinned C-plots. The variables were calculated from i=1 to i=9 in the A-plots, to i=8 in the B-plots and to i=7 in the C-plots. In multiple regression analyses the volume growth of all trees in the A-, B- and C-plots of three series, were related to tree height and to each competition variable and index value. This produced 72 regression equations. The results were:

• 1. In the A-plots,bangtree _i is the most efficient variable. Its regression sum of squares reaches a maximum for i=9. Hence, the growth of a study tree is influenced by at least nine surrounding trees.

• 2. In the B-plots,bangtree _i is also superior, the highest regression sum of squares being recorded for i=3.

• 3. In the C-plots, the regression sum of squares ofbangtree _i is highest for i=2, whereas the variabledistree _i gives the most satisfactory results.

• 4. The distance variabledistree _i gives the highest partial correlations for i=2 in the A- and B-plots and for i=3 in the C-plots.

• 5. For a given value of the competition variablebangtree ₄, the rate of volume growth in heavily thinned stands is greater than in lightly thinned. The competition variables are therefore suitable to express the degree of competition within biogroups, but not to explain differential growth rates amongst groups.