Common methods used to determine site index are based on tree height, plant composition and the use of soil maps.
[2] In the United States, site index can be determined from soil maps provided by the Natural Resources Conservation Service (NRCS).
Indirect methods include estimations based on relationships among dominant species, lesser vegetation characteristics or site indicators, as well as topographic, climatic, and edaphic factors.
A generalized model using both direct and indirect variables for developing composite site index equations was presented by Payandeh and Wang (1997).
Since it is so difficult to predict early growth rates of planted white spruce, site index curves cannot be reliably extended below about 15 years (Stiell 1976).
[8] Such variation may reflect differential expressions of check, variability within the seed lot, or the use of poorly graded stock (Stiell 1976).
[8] A fully stocked 30-year-old plantation of white spruce on a loamy fine sand underlain by silty clay loam in northern Michigan exemplifies both the variability in size of stem and their persistence.
[11] The site index curves at base age 50 years for planted unthinned white spruce at Petawawa Forest Experiment Station in eastern Ontario range between 24.38 m and 15.24 m (Stiell and Berry 1973),[7] and fall comfortably within the 30 m to 5 m range of those for interior British Columbia (Viszlai 1983, Coates et al.