CLIMATIC CALIBRATION OF 80 AEROPOLLINIC TAXA ALONG A EUROPEAN TRANSECT

The aim of calibration is to measure the relationships between climate and taxa, in order to use the taxa as indicators for the estimation o f bioclimates. The indicator capacity of a taxon (ICT) measures the pr obability of two events, together or separately, either the ordering o f abundance, within the range of a factor, or the confining of presenc es inside a limited part of the range. ICT is obtained from numbering inequalities or matches, on such orderings, without any arithmetical o peration upon the initial data. ICT measures the indicator capacity of a taxon for a factor, even if the taxon is intermittent or if its gra dient is irregular. ICT increases with the threshold of the sum of tem peratures, for some taxa, such as Arbutus, Celtis, Cistus, Coriaria, C upressaceae, Helianthemum, Olea, Onobrychis, Pistacia, Silene, Thymela eaceae. These taxa indicate a superior threshold above the classical o ne of 0 degrees C. Conversely, ICT decreases when the threshold increa ses, for other taxa, such as Abies, Aesculus, Fraxinus, Juglans, Mercu rialis, Populus, Resedaceae, Salix, Thalictrum, Tilia. A taxon may be an indicator for the whole range of a temperature, if its abundance in creases rather regularly, such as Chenopodiaceae, Erica, Olea, Plantag o, Tamarix, Umbelliferae, Vitis, or if its abundance decreases, as for Betula, Filicidae, Fraxinus, Juglans, Tilia. Conversely, some other t axa are indicators only in a part of the range, such as Calluna, Galiu m and Platanus. The indicator capacity is used to estimate the thermic climate according to the flora. For each taxon, ICT depends on A and F, which are the ranks of abundance and thermal factor. For a given ra nk A, observed in a spectrum, ICT depends on F; ICT is the probability of the spectrum to be in the rank F. The maximum value of ICT, for al l taxa in the spectrum, indicates the probable rank of that spectrum. Along the transect, the estimated temperatures happen to be equal to t he measured ones for all the tested spectra (except one) and for all t he factors, even if a small part of the flora is tested.