Use of the Lorenz curve to measure size inequality and growth dominance in forest populations

ABSTRACT

Devised in 1905, the Lorenz curve was used initially to study inequality in income distribution in human populations. Its principles have been adapted to provide measures of the size inequality between individuals in plant populations and to assess the degree to which plants of different sizes tend to dominate growth within the population. This work describes the principles on which these measures are based and the various mathematical methods available to determine their values. The potential for their use in forest populations is illustrated with an example describing their changes with age within a plantation forest stand and how these relate to inter-tree competitive processes within the stand. It is concluded that these measures have considerable value in studying the structure and growth behaviour of forest populations.

KEYWORDS:

• size inequality
• size hierarchy
• size asymmetry
• growth dominance
• growth asymmetry
• Lorenz curve
• Gini coefficient

Acknowledgements

The data for the example used here came from a major collection of eucalypt data from Australian forest owners made in 1994 through the auspices of Research Working Group 2 of the Standing Committee on Forestry of the Ministerial Council on Forestry, Fisheries and Aquaculture. The journal reviewers made useful suggestions for improvements to the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author.