• Haag, David Charles
  University of Maine
  

The relationship of four site indices and nine growth parameters of even-aged spruce-fir stands in eastern Maine to site and stand variables was determined from data collected on 50 sample plots. Regressions of site indices and growth parameters on only site variables and on both site and stand variables were formulated. Site variables included percent slope, aspect, hydrogen ion concentration and thickness of the 01, 02, A, B, and C soil horizons, depth to a pan, depth to drainage mottles, depth of rooting, percent organic matter content in the A, B, and C soil horizons, variance in thickness within and between samples of the 01 and 02 horizons, and transformations and interactions of the above variables. Stand variables included age at breast height of the overstory trees, basal area of the total stand, average height of the overstory trees, bole-wood volume, including bark, or the overstory stratum and of the total stand, and stand density.

Spruce site index, with a base age of 50 years at breast height, when regressed on only site variables, was related positively to the variance in thickness within samples of the 02 horizon, percent organic matter in the C horizon, thickness of the A horizon, and decomposition ration of the organic pad and related negatively to the variance in thickness between samples of the 02 horizon, percent slope, thickness of the 01 horizon, and interaction of percent coarse material and percent fine material in the B horizon.

Fir site index, with a base age of 50 years at breast height, when regressed on only site variables, was related positively to the pH of the 01 horizon, bulk density of the 02 horizon, and thickness of the solum and related negatively to the bulk density of the B horizon.

Regression equations were also formulated for best site index and average site index, based respectively on the height of the tallest tree, spruce or fir and on the average of the site index values of the six tallest trees, spruce and/or fir, on the sample plot.

Other growth parameters for which regressions on site and stand variables were formulated included past five-year growth in height of the overstory trees, mean annual growth in height of the overstory trees, past five-year area growth of the overstory stratum, mean annual basal area growth of the overstory stratum, mean annual basal area growth of the total stand, mean annual growth in bole-wood volume, including and excluding bark, of the overstory stratum, and mean annual growth in bole-wood volume, including and excluding bark, or the total stand.

In all regression equations, except the regression of fir site index, the inclusion of both site and stand variables as independent variables increased the coefficient of determination and decreased the standard error of the mean. The regression of fir site index remained the same in both instances.