Studies dealing with the identification of plant functional traits as indicators of an individual or species ecophysiology have become abundant in the literature. Overall, this approach is important for generating proxy data for fundamental physiological traits that are, in general, much more challenging to measure. This popularity in the functional trait approach has now resulted in a host of traits referred to as functional in the literature, but often without specific associations with ecophysiological performance among individuals, species, or habitat types. Most often, correlations are made with the general habitat of occurrence, while fewer studies exist that document direct cause and effect relationships. Moreover, the large number of traits now identified as functional has complicated the choice by investigators of traits for study that might best reflect ecophysiological performance. We report here quantitative results of a literature survey of studies identifying and utilizing functional plant traits, a total of over two hundred publications. We also ranked all traits numerically according to their frequency of occurrence, plus the total number of authors reporting particular traits as functional. A total of 107 traits were identified as being functional, although only a few dominated the studies. We first point out conceptual problems when interpreting the ecophysiological significance of the most commonly studied trait in the literature, specific leaf mass (LMA) and its inverse, specific leaf area (SLA). We also discuss briefly the importance of a priori identification of more mechanistic, co-evolved suites of functional traits for evaluating plant adaptations leading to observed distribution patterns.
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