Relative plant growth revisited: Towards a mathematical standardisation of separate approaches

The concept of relative growth has independently been developed and pursued in different fields of science and at different locations. It has proved to be useful in comparative studies of plant growth analysis. The purpose of this review is to provide a synthesis of different independent approaches as well as of research applications and to standardise the mathematical notation in order to facilitate future research. In the context of ecology, we explore and analyse the definitions of absolute and relative growth rates, growth acceleration, growth multipliers and allometry from a mathematical point of view. In addition, we evaluate statements made in the literature, compare different concepts that have been developed separately and show how they relate to each other. We also review and standardise functions of absolute and relative growth, which can be used for analysing and modelling plant growth. Finally, we comment on sampling, growth rate combinations and the recently discussed method of size standardisation. We conclude that the different approaches to quantifying and modelling relative growth rates can conveniently be integrated in one consistent theoretical concept and as a result provide useful synergies. A harmonisation of different definitions of relative growth rate is straightforward and a consistent, meaningful notation provides a deeper understanding of the concept. Relative growth rates are key characteristics for assessing growth performance and growth efficiency. Recently they have gained importance for diagnosing and modelling mortality and reproduction processes and they potentially play a crucial role in reconstructing growth processes in dendrochronology, climate change and forest decline research. From a technical point of view, relative growth rates are more straightforward to model than absolute growth rates and more emphasis should be devoted to model development. (C) 2015 Elsevier B.V. All rights reserved.