Condensed tannins (CTs), a dominant class of plant secondary metabolites that often occurs a large amount in plant tissues, potentially regulate ecosystem processes such as herbivory, soil decomposition process and nutrient cycling in an ecosystem. Therefore, elucidation of regulating factors that determine the distribution and abundance of CTs can be the first step for better understanding of ecosystem processes. In this study, factors affecting the abundance of CTs were assessed by illustrating the global distribution pattern of CTs with a meta-analysis.My data set was compiled by conducting keyword search using SCOPUS. Combination of following keywords were used in the database search: “condensed tannins”, “herbivory”, “decomposition”, and “leaves”. Each study to be included in this study had to satisfy following criteria: The concentrations of CTs in tree leaves were measured by acid-butanol assay, and the tree individuals grew under the natural condition. With the collected publications, climatic parameters (i.e., air temperature in the growing season and annual precipitation), latitude, and methodological conditions (i.e., extract solvent, and standard substance for calibration) as well as the concentration of CTs were collected. Finally, I obtained 805 values of the concentration of CTs in 72 study sites from 26 individual studies, in addition to climatic, positional, and methodological data.

Results/Conclusions

The maximum and median values of the concentration of CTs reported within one research site were increased with increasing air temperature in the growing season. The minimum value of concentration of CTs within one site decreased slightly, but significantly, with increasing annual precipitation. Latitude positively correlated with the maximum values of the concentration of CTs within one site, but this trend was only marginally significant. Measurement methodologies (extract solvent and standard substance) also affect the quantification results of CTs. However, the general trends were still kept after the separation of my data set into each methodological category. My study suggested that the abundance of CTs in leaf tissues could be primarily regulated by air temperature in the growing season, and that may implied the primary ecological significance of CTs could be a role as anti-herbivore substances since herbivore pressure increased with increasing air temperature. Recent global warming, therefore, may change the distribution and abundance of CTs, and in turn, may alter the decomposition process and nutrient cycling in an ecosystem.