For each stratum, surveyors have to choose the species that GI data will be collected on. This species is called the site index species.
Normally, the leading species in the stratum's inventory label is chosen as the SI species. This ensures that the SI data collected in the field is compatible with the requirements of forest cover map labels and the inventory database, as well as ISIS and MLSIS.
The inventory component leading species is not an appropriate choice for site index species when it is:
Whenever this is the case, the silviculture component leading species should be chosen for the site index species.
The Code requires that SI be provided in both the inventory and silviculture labels. If the inventory and silviculture labels have different leading species, two different SI values are required. Surveyors can either collect GI data on one tree of each species in each plot or they can collect GI data on one species and use the SI conversion table to estimate SI for the other species. SI species conversion is explained in Lesson 10 of this workbook. Obviously, collecting GI data on both species will give higher accuracy.
For a stratum, a tree species is suitable as a SI species if (Figure 5.4):
Height growth above DBH may not reflect long term site productivity if the stand has experienced wide spread damage, thinning shock, fertilization or brush competition. A stand is not suitable for the GI method if these factors have altered the normal height growth. More research is needed on this subject.