Once species are selected, collect as much information on them as possible to verify that they are the best available choices. After preliminary selection of NFTs, further research is needed to determine if selected species are native or naturalized in the area of interest. If species are present, their physical appearance would give an indication of how well they are adapted. If species are not present, then simple field trials should be conducted to determine how they will grow at the site. Field trials to evaluate exotic species In a Guide to Establishing Research and Demonstration Plantings with Nitrogen-Fixing Tree Species, Macklin et al.
Trials normally involve unreplicated plots of a relatively large number of potential species.
Soil and climatic conditions at the trial site should be similar to the entire planting area. If the planting area includes different environments, a trial should be in each environment. It is important to select a homogeneous site for the trial to eliminate differences in soil fertility, water availability, etc. between plots. Tree spacing should be 1 m x 1 m or 2 x 2 m. The closer spacing is appropriate for trials that will be maintained for only a year or two.