Raunkiaer was sensitive to an early major criticism of his initial statistical approach, namely, that the frequency of a particular life-form is gauged by the number of species possessing it and thus does not reflect the abundance of species possessing each life-form. Life-form spectra for an entire flora covering a sufficiently large area may be useful for classifying vegetational settings in terms of their phyto-climates. However, within local or even regional areas, the effects of local climatic variables are likely more accurately revealed when spectra are modified to account for the abundance, frequency, or coverage of each of the various species and their ecological importance. Raunkiaer's early statistical approach was subsequently modified in response to this concern by 'weighting' the life-forms of species according to the frequency with which the species possessing them occur. This refinement sheds considerable light on a number of ecological phenomena, such as successional changes in community physiognomy.
Another concern, which applies to any classification system purporting to correlate life-forms with climatic conditions, is the tacit assumption that the feature or features used to classify life-forms accurately reflect ambient environmental conditions (e.g., the position of renewal buds in the Raunkiaerian system). The extent to which a causal connection exists between climate and morphological types identified on the basis of one or more criteria requires refined and extensive ecophysiological analyses. However, it must be noted that life-form classification systems are necessary for any objective inductive study of vegetation, that is, the factual description of the physiognomy of floras.
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