A Light-Adjusted Growth Intercept Model for Predicting White Spruce Site Index

One of the challenges of managing spruce-aspen mixedwoods in the boreal forest is the difficulty in determining site index for spruce in those stands in which it occurs primarily in the understory. A study was conducted to determine if growth increment of understory spruce, adjusted for available light, could predict spruce site index. In each of nine stands, spruce site index was determined for three dominant trees. Available light (measured as proportion transmitted) and growth increment (estimated by the growth intercept method) were recorded for three to eight understory spruce per stand. Growth increment adjusted for available light predicted spruce site index better (R2 = 0.56 or 0.63, depending on the model used) than unadjusted growth increment (R2 = 0.10), thus indicating the potential for using light-adjusted growth increment to predict site index.