The spatial distributions of two species of tree result in a bivariate pattern. This pattern characterizes biological mechanism involved within a forest with the spatial localization of the trees. If we consider simultaneously two species, the main question is not to describe the marginal distribution of each species but to describe the relationship between the repartitions of the two species under study. The relationship between two clouds of points can be described in various ways and therefore many indices can be defined. Each index will give a specific information about these relationships and will greatly depends on the ecological mechanisms, i.e., the point process that leads to the observed repartition. The aim of this article is to review the leading indices in ecology and to provide guidelines for practical use. To mimic ecological situations, we simulated 13 point process that can model classical relationships between two species of trees and compute nine classical indices. The interest of the various indices are discussed. A R package for simulating the point process and to compute the indices is available on request. The package is available upon request at picard@cirad.fr or avner@inapg.fr.