Estimating site quality from early height growth of white spruce and red pine plantations in the Thunder Bay area

Abstract

Growth intercepts and breast height-age height growth curves were developed for estimating the site quality using early height growth in white spruce {Picea glauca (Moench) Voss) and red pine (Pinus resinosa Ait.) plantations in the Thunder Bay, Ontario area. These methods for estimating site quality were developed from height growth data obtained using annual node measurements and stem analyses of three dominant, undamaged, trees in each of 46 white spruce and 25 red pine plots located throughout the Thunder Bay area. White spruce growth intercepts were computed using series of one through seven internodes from eight starting heights between 0 and 3.0 m. Red pine growth intercepts were computed using series of one through 10 internodes from the same eight starting heights. The best estimates of white spruce and red pine site quality were obtained from the average length of the first three, four, and five internodes above 2.0 m, and the first three, four, and five internodes above 1.5 m, respectively. Both white spruce and red pine height growth patterns were best described by an expanded Chapman-Richards function capable of expressing polymorphic height growth patterns. These height growth patterns compared well with those of eastern Ontario and the Lake States. Height growth below breast height for both species was very erratic and was not related to site quality. Consequently, total height-age height growth curves that included this early erratic height growth did not provide accurate estimates of site quality in these white spruce and red pine plantations. Growth intercepts provided accurate estimates of site quality in early years. However, breast height-age height growth curves provided more accurate estimates of site quality when plantations exceeded the ages required for these growth intercepts.