(2)
A positive value of L(r) indicates clustering over that spatial scale
whereas a negative value indicates dispersion.
The contagion index \(W_{i}\) described the degree of regularity of the
spatial distribution of the four trees nearest to a reference tree i.\(W_{i}\) was based on the classification of the angles between these
four neighbors. A reference quantity was the standard angle\(\alpha_{0}\), which was expected in a regular point distribution. The
binary random variable \(z_{\text{ij}}\) was determined by comparing
each \(\alpha_{j}\) with the
standard
angle \(\alpha_{0}=90\), and the contagion index \(W_{i}\) was then
defined as the proportion of angles \(\alpha_{j}\) between the four
neighboring trees which were smaller than the standard angle\(\alpha_{0}\):