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Les plantes indicatrices du climat en France et leur télédétection

Abstract : From its beginnings, the botanical geography has recognized the influence of the climate on the distribution of the plants thanks to the comparison of territories and the study of climatic and floral limits. It has expressed this influence with maps rather than measurements. It has progressively given birth to a biological discipline, the plant ecology, which blends, in a natural environment, with field observations and with numerical treatments. But this discipline has mainly measured the most readily available field variables, namely those which concern the substrate of the vegetation rather than its climate, at least on a large scale. This discipline has today a climatical data bank, the one from Météo-France, and a floral data bank “Sophy” at its disposal. It can establish relations between plants and climates on a field and numerical basis, and is therefore more objective, more precise and more complete than the botanical geography.
The national meteorological network delivers standardised data from 828 stations in France. Among the most active factors on the plants, there are the day and the night temperatures, month by month, reflected respectively by the monthly maximum and minimum temperatures; there are also the amounts and the monthly frequencies of rainfall. These factors are reduced to an equal period of reference after estimation of the missing data. The bank ‘Sophy' for its part supplies the presence and the abundance of 4 500 botanical taxons from 140 000 stations in France. It allows to
distinguish the behavior of a plant be it by its presence or be it by a threshold of abundance. The conjunction of the two banks supplies a sampling of about 12 000 floral stations distributed between the climates of 574 stations.
The apparent dependance of a plant on a factor is shown by the concentration of its presence on a factor scale. This concentration can be calculated as a probability and it follows a rigorous unimodal gradient on the factor scale. The maximal concentration expresses the power indicator of the plant in a way that this parameter is only zero for an omnipresent plant. This power indicator is all the more elevated the better the plant is indicative. The maximum concentration rank indicates the
optimal position of the plant. The twelve power indicators and the twelve optimal positions summarize the behavior of a plant on the factor scale. This work presents the catalogue of behaviors
for 2 800 plants indicative of the climate and for six climatical sizes in graphic form. The catalogue also presents the geographical distribution of all plants among the 140 000 field stations of the
‘Sophy' data bank. This catalogue is not only an ecological dictionnary of climate indicative plants. It is also an information tool which allows to estimate with precision the climate in a community which is deprived of a meteorological station and which therefore allows to introduce the climate in a numerical way in all phyto-ecological studies in France.
Apart from the above mentioned application, the catalogue does not show a synthesis. It is completed by a climatic classification of plants which show the hierarchy of phenomena and their
statistical importance. This classification determines the plant groups having similar behaviors according to their accuracy accumulated in the ranks of the climatic variables. It characterises a group by its indicative powers and its optimal positions. It ends in a catalogue of principal groups, from the most numerous and the most different, forming the leading levels of synthesis, to the most detailed. It shows that the major phytoclimatic gradient separates the coast, the Mediterranean
region and the mountains of the continental plains. The coastal group, for example, can be subdivised in Atlantic and Mediterranean groups, then in subgroups confined to only a part of each climate.
A similar work has been done concerning the relations between the plants and the variables of the satellite NOAA. As in the botanical geography, the relations between plants and satellite measurements are often founded on the superimposition of these images, based on a vegetation index (NDVI = Normalized Difference Vegetation Index), with vegetation charts. These images and their interpretation show large vegetation categories, like forest and farming formations. The bank ‘Sophy' allows an observation study and not only a cartographic study of the phenomenon. This bank links the floral data with the satellite data given of the same place, in 11 000 pixels of 5,5 km to the side. The monthly synthesis of the NDVI shows the differences of behavior between the plants of different formations, like the grassland, forests, ripisylves (vegetation of humid zones), Mediterranean formations and the Atlantic moors, coasts and mountains. The power indicators are sometimes high and similar for the plants of the same formation. But they are still showing some incoherences, be they from one month to another, be they from one satellite variable to another, for want of an insufficiant standardisation in the characterisation of the pixels. Standardised satelllite variables over a longer period, missing data of which could be calculated, might be capable to
localise phytoclimates, thanks to the groups of plants they represent, and to generalise in the field the observation knowledge of the phytoclimatology.
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Submitted on : Friday, February 11, 2005 - 10:33:00 AM
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Emmanuel Garbolino. Les plantes indicatrices du climat en France et leur télédétection. Ecologie, Environnement. Université Nice Sophia Antipolis, 2001. Français. ⟨tel-00008446⟩



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