Comparison of phytophenological data: a proposal for converting between GFI and BBCH scales.

Phenological scales used in the past were not standardized: in different countries different methods were followed and these are often still in use today: for example Italian Botanists usually make the phenological observations by means of the GFI key, adopted in 1993 by the Italian Phenological Gardens, or by Marcello’s Key. The comparability of data collected with different methods is a serious problem, so, in the last 20 years the scientific community has directed significant efforts toward the standardization of sampling methods and phenological scales: in Europe, the BBCH scale (Meier, 1997) has been generally adopted. Although the BBCH and GFI scales have different structures, several stages are corresponding. We present a method for the conversion between BBCH and GFI scales, based on the numerical relationship between the codes of the respective stages: in the reproductive cycle the relation is well approximated by a sigmoid function, while in the leaf development, by a linear function. The presented method also allows the fractional values of the stages to be converted (e.g. the average value of a population). Keywords: Phenological scales, BBCH, GFI, growth stages, flowering, leafing