Relative Growth Rates: a Critique

Abstract

Forest researchers frequently use mean relative growth rates to compare growth of seedlings that differ in initial size. Reasons for using the technique include: 1) to eliminate any size-related growth differences, and 2) to determine which seedlings are inherently more “efficient.” Although this technique is based on the theory that tree growth occurs as a constant percentage of initial size (the compound interest law), researchers apply this technique even when the percentage increase changes with increasing size (the variable interest law). However, such use may lead to faulty conclusions. Several alternative methods of analysis have been proposed to overcome the problems inherent when comparing mean relative growth rates. One potential alternative is the incremental growth analysis method that changes the basis of comparison from trees of equal age to trees of equal size. This method involves plotting the absolute growth rate (e.g. current annual increment) as a function of size at the beginning of the growth interval.