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Abstract
When explaining the dynamics of individual trees, the incorporation of size and distance of neighboring trees into a model can improve the prediction of growth and mortality. Several methods have been proposed to define the number of competing trees based on variable zone radii and the principles of angle count sampling. The task of measuring position-dependent competition indices appears to be ideally suited for permanent sample plots and long-term studies of growth and yield (production), where the marginal effort of remeasurement is concentrated on measuring size attributes of survivor trees and the occasional distance of a new sample tree. The proposed competition index is based on point sampling with a variable basal area factor (BAFV) that is partially derived from the Spurr (1962) competition index. Point sampling is a fast, easy, and inexpensive methodology for selecting the number of competing trees, and the new BAFV methodology proved to be very efficient for estimating growth. With the selection of an appropriate basal area factor, it is possible to reduce the number of subject trees and competition trees in the sample, and eliminate the need for edge correction methods. Although the index value assigned to the subject tree using the BAFV is biased, an appropriate correction is presented and discussed. The average competition index obtained from using the corrected value for the subject tree and the BAFV for the competing trees equals the stand level estimate of basal area.
Highlights
When a competition index is used to describe an individual tree’s social status and quantify the surrounding environment, it is labeled as one-sided competition [1]
The methodology proposed here creates an absolute value of competition for the subject tree rather than a dimensionless competition index
Moving the point center from a probability based location to the center of the subject tree inflates the estimate of basal area for the subject tree and results in a bias
Summary
When a competition index is used to describe an individual tree’s social status and quantify the surrounding environment, it is labeled as one-sided competition [1]. The first step determines the count and which trees are labeled as competitors, while the second step determines their size and distance. Several authors have indicated the superiority of selecting neighbor trees for the first step with angle count sampling ( known as point sampling, variable plot sampling, or the Bitterlich method [3,4]). Other authors [5,6] have presented alternative methods for selection of competitor trees in forests of Eucalyptus globulus and Betula pendula, respectively. It is affirmed, that any fixed-radius method proves disadvantageous when it is utilized in long-term growth studies [2]
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