Definition of an arboretum: "Park devoted to the experimental cultivation in open ground of trees and shrubs belonging to different generally exotic species, with a view to studying their behavior. An arboretum constitutes a directory of trees and shrubs in in which individuals are labeled with their common and scientific names, as well as their continent of origin. Its objective is at the same time scientific, educational and aesthetic. The species are classified either by family, or by ecological station or by geographical origin. " (Large encyclopedic dictionary Larousse)

There are 3 types of arboretum:

- the collector's arboretum, like that of Forrières.
It consists in observing the adaptability of exotic species in our soil and climate conditions;

- the forest arboretum. This only includes species likely to be used for wood production. The plots have at least a few ares and must make it possible to assess the behavior of the species in population as well as the variability of the individuals;

- the geographic arboretum. As its name suggests, groups together woody species by geographic affinity, creating mixtures of species characteristic of the same type of forest.

Some varieties have been tested in collection arboretums and then planted massively in Belgium such as douglas, Corsican pine, Austrian black pine, American red oak, etc.