The Life Zone System

Holdridge m'a envoyé en réponse à mon article : « Conceptions modernes en bioclimatologie et classification des formations végétales » Adansonia 5,3 : 1963) la note suivante en me demandant de la publier dans Adansonia, ce que je fais bien volontiers.J'aurai d'autres occasions de revenir plus tard sur un sujet qui est de toute première importance pour l'écologie des régions tropicales. A. AubrévilleOn pages 297-306 of Fascicule 3, Tome V of the journal Adansonia, Prof. A. Aubréville has published a discussion of both the potential évapotranspiration concept of C. V. Thornthwaite and my life zone, bioecological classification System.Relative to the latter, I hâve put together the following notes to clarify some of the spécifie questions raised.The life zones of my System as defined in précisé numerical ranges of mean annual précipitation, mean annual biotemperature and potential évapotranspiration ratio on the chart are only first order divisions of the climates and vegetational groupings on the land areas of our planet.The chart, originally published in 1947, was constructed mainly on the basis of preceding expérience and publications of many ecologists, climatologists, botanists, pedologists and other scientists with some contri¬ bution from my own findings in the tropics.Since the chart was first assembled with only température and précipitation values, my particular contributions were the use of a new value, that of biolemperalure, for showing température relations, the finding that significant guide fines of biotemperature and précipitation should be spaced in accordance with logarithmically increasing values and the arrangement of a set of hexagons, as determined by the guide fines, so as to define natural units in the field as well as clearly show their climatic relationships to other life zones.Although the chart is presented in two dimensions, it actually represents a threedimensional figure, an important aspect not mentioned by M. Aubréville.At higher élévations the biotemperature and précipi¬ tation values are the same as those for life zones of cooler latitudinal régions Source : MNHN, Paris