If the context and end-uses are clearly defined, then selection of species and their provenances (i.e. geographic source) can be started. There are four levels of approach, all of which may need to be taken to reach a reliable choice.
(1) A certain degree of choice can be made from a knowledge of the species' natural habitat, biological and reproductive characteristics. There are many reference sources that can provide this basic information, and which are constantly being updated. An aim will be to match source and planting publication conditions as closely as possible, on the principle that such trees will be best adapted. As a general rule, local (indigenous or native) species should be considered first, before going on to consider introduced (exotic or alien) species.
(2) Existing species, provenance, clonal or other trials, or routine plantations on similar publications can be used to get an idea of how different sources will perform. Again, there may be a lot of information available in say, species monographs or datasheets, that could be consulted to help make a choice. The species' performance over as long a period as possible should be obtained, so as to identify any potential problems.
(3) Despite already existing information, there is usually a need to confirm choices (especially where large scale plantings are envisaged) by carrying out trials of the proposed species / sources in the same geographic area. This is because there are many unknown factors that may effect the eventual performance of a species, such as weediness, disease, or flowering. Ideally, trials should continue until the trees become mature, and not just look at initial performance over, say, 510 years.
(4) Many species cover a wide and variable geographic area and climate. This means that there is likely to be a wide genetic variation within the species, according to the species' source or provenance. Some species may have their provenance regions defined. Each region should indicate sources that will be more or less similar genetically. If there is a great range of provenances, then trials of the most promising will also be required, as well as species trials.
A current "hot" issue is whether local or introduced species should be used. Species such as Eucalyptus, Pines and Teak, have formed the bulk of commercial plantations outside their natural ranges. In these cases, decisions can be complicated and will need to take into account environmental, social and cultural issues, as well as the purely technical. There are potentially serious problems associated with introduced species, such as invasiveness, that only recently have been adequately recognised.
See UNDERSTANDING CURRENT ISSUES for more details of these problems.