Population Dynamics in Loblolly Pine Stands: Changes in Skewness and Size Inequality

Abstract

We determined the changes in size inequality and asymmetry that occurred over a 50—yr period in 16 even—aged, naturally seeded populations of Pinus taeda. Initial densities ranged from 618 to 28 861 stems/ha. We used these data to test four predicted trends in size structure. We found that (1) in young stands size inequality was greater at higher plant densities, (2) skewness of tree volumes was significantly greater at higher initial densities, whereas skewness of diameters was not, (3) size inequality increased significantly prior to the onset of self—thinning, then decreased during self—thinning, and (4) skewness did not increase before self—thinning or significantly decrease during self—thinning. Numerous measures of size distribution have been employed to assess competition in plant populations, including various measures of inequality and skewness, as well as parameters of fitted distributions such the Weibull distributions. We found the two—parameter Weibull distribution only moderately effective at capturing the forms of the distributions observed. Correlations showed very close linear relationships among the Gini coefficient, the coefficient of variation, and the shape parameter of the Weibull distribution–both within and across different measures of tree size. All three statistics were correlated with initial density. Skewness coefficient for distributions of diameter, height, and volume were not closely correlated with each other population characteristics. We recommended measures of inequality as more suitable for summarizing biologically important properties of tree populations than measures of skewness or skewness—sensitive parameters of probability distributions.

Upland black spruce stand development 17 years after cleaning and precommercial thinning

“…The Forestry Chronicle Downloaded from pubs.cif-ifc.org by 34.218.44.141 on 05/10/18 ence of competing hardwoods. The increase in the black spruce D Weibull shape parameter with decreasing density may reflect greater negative skewness (Bailey and Dell 1973) and reduced size variability (Knox et al 1989). Both density-dependent mortality and thinning from below had similar effects on the shape parameter, producing less variable but left-truncated and more negatively skewed diameter distributions through preferential removal of smaller trees.…”

Développement d’un outil de classification de la structure des peuplements et comparaison de deux territoires de la pessière à mousses du Québec

“…Le coefficient de variation et surtout le coefficient d'asymétrie et l'indice de diversité de Shannon-Wiener ont été largement utilisés dans la littérature pour décrire la distribution diamétrale des peuplements (Knox et al 1989, Buongiorno et al 1994, Groot et Horton 1994, Kubota 1995, Wikström et Eriksson 2000, Staudhammer et LeMay 2001, Takahashi et al 2001. Toutefois, ces indices ont rarement été utilisés de façon combinée, même si individuellement, leur capacité à décrire les différents types de distribution comporte certaines faiblesses.…”

Wind Stability of Commercially Important Tree Species and Silvicultural Implications, Daegwallyeong Korea

“…We used Gini coefficient (Weiner and Solbrig, 1984) to characterize DBH size inequality. Lorenz curve is the curve below the 45º line gained by plotting the cumulative frequency of tree population and cumulative frequency of basal area (Knox et al, 1989;Nilsson, 1994;Stöcker, 2002). In order to draw the curve, trees in the stands were sorted by increasing dbh order, then the cumulative tree number and basal area were calculated.…”

“…At the tree and stand scale, silvicultural regimes can be designed to promote tree and stand acclimation to wind and minimize damages (Mitchell, 2013). The Gini coefficient and coefficient of variation have been identified as the most useful descriptors of the size variation in forest stands (Weiner and Solbrig, 1984;Benjamin and Hardwick, 1986;Knox et al, 1989) which, in turn, is a useful predictor of a measure of stand stability (Wilson, 1998).…”