Population density influences assessment and application of site index

The height growth of dominant trees in plantations is often assumed to be i ndependent of initial planting density. This assumption allows for the use of dominant tree height as an index of site quality. We found that this ass umption was false for the seven tallest trees in 184 even-aged loblolly pin e (Pinus taeda L.) stands, planted at nine initial planting densities, at f our different geographic locations. A strong, highly significant negative c orrelation was found between dominant height and initial planting density f or stands 14 and 16 years of age. This leads to large differences in predic ted site index for stands with different initial planting densities planted at the same geographic location. Use of these site indices to predict yiel d produced large differences in predicted yield (m(3)/ha) at age 25. These results provide strong evidence for density-dependent height growth, even f or dominant trees in the stand, and suggest that site index, used as a meas urement of site quality, is confounded with stand density.