THE RELATIONSHIPS BETWEEN STAND DENSITY, CROWN SIZE AND BASAL AREA GROWTH IN STANDS OFPINUS TAEDAL. IN THE NATIVE HABITAT OF THIS SPECIES.

Abstract

Summary Regression equations are derived in which relationships are established between stand density, crown size and basal area growth in pure, even-aged stands of P. taeda L. in the Piedmont of North Carolina, U.S.A. The findings are based on observations on 129 tenth-acre sample plots of variable stocking, age and site index. It is shown that: Single trees of given d. b.h. make more than twice as much basal area growth when basal area per acre is 60 square feet as when basal area is 140 square feet. Single trees of large diameters may make more than twice as much basal area growth as trees of relatively small diameters when basal area per acre is fixed. Basal area growth per acre generally increases as stocking in basal area declines from 140 to 60 square feet per acre. However, basal area growth per acre at relatively high stockings may be greater than basal area increment at lower stockings when the average d.b.h. of the trees at the high basal area is comparatively small. Basal area growth per acre at any fixed stocking in basal area per acre increases as the number of trees that compose the stand increases from 50 to approximately 350 trees per acre. After that, higher counts per acre are not associated with significantly greater basal area increments. Basal area growth per acre decreases linearly as stand age increases from 20 to 60 years when number of dominant and codominant trees per acre, and basal area per acre, remain constant. The rate of basal a rea increment of single trees increase generally as stand age increases from 20 to 60 years. There is a marked levelling off in the rate of increase after the 35th year. The rate of increase is greatest in stands maintained at relatively low basal areas (through a reduction in numbers of trees as basal area per tree increases). Basal area increment per acre increases proportionally as site index increases from 60 to 100 when other independent variables are at their mean values. The relative crown surface area of single trees of a given d.b.h. is nearly four times as great when basal area per acre is 60 square feet as when basal area per acre is 160 square feet. Basal area increment per acre increases linearly with relative crown surface area when other independent variables are at their mean values. A fixed relationship exists between relative crown surface area and crown length when the latter is expressed as a percentage of tree height.