Climatic definitions of the world’s terrestrial biomes

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Prepared by Javier Loidi, Gonzalo Navarro-Sánchez and Denys Vynokurov

Domains, Ecozones, Biomes and Subbiomes of the Earth. Distribution of the 20 subbiomes across the world. 1a Polar tundra, 1b Tundras of the temperate mountains in cryoro belt, 1c Tundras of the tropical mountains in cryoro belt, 2a Lowland boreal Taiga, 2b Forests and shrublands of the temperate oro belt, 3a Temperate deciduous forests, 4a Lauroid evergreen forest of the lowlands, 4b Conifer coastal forests, 4c Tropical montane cloud lauroid and conifer evergreen forest, 5a Oceanic sclerophyllous-microphyllous evergreen forests and shrublands (Mediterranean), 5b Continental scrub and woodlands, 5c Patagonian shrubland, 6a Forest-steppe, 6b Grass-steppe, 7a Cold deserts and semi-deserts, 7b Temperate deserts and semi-deserts, 7c Warm deserts and semi-deserts, 8a Tropical xeric shrublands and woodlands, 8b Tropical pluviseasonal forests and woodlands, 9a Tropical rain forests.

The aim to describe the world’s vegetation on a global scale in a way that reflects the factors that determine its distribution is as old as Geobotany itself, since the early 19th century. Several attempts have been made over these 200 years, and we present our approach in this work. To achieve this goal successfully, two things are needed: a scheme of broad-scale descriptive units dependent on the main factors that shape ecosystems on such scale, and an extensive knowledge of them. The main factor shaping ecosystems distribution at this scale has been climate. We consider it feasible and useful to establish a classification of large biotic units of the world related to climatic types. The CHELSA repository provides climatic data at high resolution for the earth’s land surface areas. We have extracted 616 localities selected to represent the biotic units we have recognized. With them their bioclimatic characterization has been established by means of climatic data analysis. The biotic units have been organized in a hierarchical classification: the highest level are the domains (Cryocratic, Mesocratic, Xerocratic and Thermocratic), divided into seven ecozones, which are divided into nine biomes and these, in turn, into 20 subbiomes. Most of these biotic units are intercontinental. The mountains represent an abbreviated version of the latitudinal zonation, and the altitudinal belts are related to the corresponding units of the lowlands. For the bioclimatic units, a parallel classification is proposed to fit with that of the biotic units: four Macrobioclimates and ten bioclimates. Furthermore, ombrotypes and thermotypes are recognized to frame the climatic variation within each climatic territory due to terrain ruggedness, particularly in relation to large or medium-sized mountains. We have the following conclusions. 1) There is a homology between the latitudinal and altitudinal zoning of biotic units: the upper level in the high mountains is homologous to the polar units (altitude resembles latitude). 2) The southern hemisphere is substantially more oceanic than the northern one. This is due to the distribution of the land masses on the earth and the modifying effect they have on the flow of air and marine currents. 3) The western side of the continents shows a different zonation of biotic units compared to the eastern sides: the biotic unit of the deserts and that of the Mediterranean occur in their western sides and expand in their interior favoured by rain shadow and continentality effects.

Representation of real and virtual areas of the nine biomes across latitude and altitude in profiles of the continents. A and B are North-South profiles from the western side of the continents (A The Americas from the Pacific; B Europe and Africa from the Atlantic), and C and D are profiles from the eastern side (C The Americas from the Atlantic; D Asia and Australasia from the Pacific). E Represents a transect in the middle of the Asian continent, continuing with the profile of Africa from the Indian Ocean. Inland the colours are darker than in the air, representing only a virtual area. 1 Tundra; 2 Boreal forest; 3 Temperate deciduous forest; 4 Temperate pluvial evergreen forest, shrublands and grasslands; 5 Temperate aridiestival evergreen forests and shrublands; 6 Steppes; 7 Deserts and semi-deserts of arid regions; 8 Tropical pluviseasonal forests and shrublands; 9 Tropical rain forests.

This is a plain language summary for the paper of Loidi et al. published in Vegetation Classification and Survey (https://doi.org/10.3897/VCS.86102).