Diameter Distribution and Growth of Loblolly Pine

Abstract The relationships between cubic-foot growth and diameter distribution, and residuals from cubic-foot growth equations and diameter distribution were tested on 103 plots of even-aged managed loblolly pine. A series of diameter distribution characterizations using mathematical expressionsof the entire distribution curve, mathematical expressions of individual attributes of the diameter distribution curve, and biological characterizations of it were computed. The gamma distribution and cumulative frequency distribution by dbh classes of the Pearl-Reed population growth curvewere computed. Average dbh, number of trees per acre, and the range of tree diameters were ascertained. The second, third, and fourth moments, as well as the standard deviations, the coefficients of skewness, and the coefficients of excess were calculated. Biological characterizations of theright-hand tail of the diameter distribution included ratios of basal area in various percentages of the tail in number of trees to total basal area as well as an expression involving number of trees. All of the 15 expressions of diameter distribution were rejected as useful expressions forcharacterizing merchantable cubic-foot growth. The probability of markedly reducing unexplained variation in merchantable cubic-foot growth in managed, even-aged loblolly pine with characterizations of diameter distribution is small.