The Holdridge life zones system is a global bioclimatic scheme for the classification of land areas. It was first published by Leslie Holdridge in 1947, and updated in 1967. It is a relatively simple system based on few empirical data, giving objective mapping criteria. A basic assumption of the system is that both soil

Soil type

In terms of soil texture, soil type usually refers to the different sizes of mineral particles in a particular sample. Soil is made up in part of finely ground rock particles, grouped according to size as sand, silt and clay...

 and climax vegetation

Climax vegetation

Climax vegetation is the vegetation which establishes itself on a given site for given climatic conditions in the absence of anthropic action after a long time ....

 can be mapped once climate is known.

While it was first designed for tropical and subtropical area, the system applies globally. The system has been shown to fit tropical vegetation zones, Mediterranean zones, and boreal

Boreal ecosystem

The term boreal is usually applied to ecosystems localized in subarctic and subantarctic zones, although Austral is also used for the latter....

 zones, but is less applicable to cold oceanic or cold arid climates where moisture becomes the determining factor. The system has found a major use in assessing the possible changes in natural vegetation patterns due to global warming

Global warming

Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

.

The three axis of the Barycentric subdivision

Barycentric subdivision

In geometry, the barycentric subdivision is a standard way of dividing an arbitrary convex polygon into triangles, a convex polyhedron into tetrahedra, or, in general, a convex polytope into simplices with the same dimension, by connecting the barycenters of their faces in a specific way.The name...

s are:

• precipitation
  Precipitation (meteorology)
  In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
  
   (annual, logarithmic)
• biotemperature (mean annual, logarithmic)
• potential evapotranspiration ratio (PET) to mean total annual precipitation.

Further indicators incorporated into the system are:

• humidity
  Humidity
  Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
  
   provinces
• latitudinal regions
• altitudinal belts
  Altitudinal zonation
  Altitudinal zonation in mountainous regions describes the natural layering of ecosystems that occurs at distinct altitudes due to varying environmental conditions. Temperature, humidity, soil composition, and solar radiation are important factors in determining altitudinal zones, which consequently...
  
  

Biotemperature is based on the growing season length and temperature. It is measured as the mean of all temperatures above freezing, with all temperatures below freezing adjusted to 0 °C, as plants are dormant at these temperatures. Holdridge's system uses biotemperature first, rather than the temperate latitude bias of Merriam

Clinton Hart Merriam

Clinton Hart Merriam was an American zoologist, ornithologist, entomologist and ethnographer.Known as "Hart" to his friends, Dr. Clinton Hart Merriam was born in New York City in 1855. His father, Clinton Levi Merriam, was a U.S. congressman. He studied biology and anatomy at Yale University and...

's life zones, and does not primarily consider elevation. The system is considered more appropriate to the complexities of tropical vegetation than Merriam's system.

Classes

The classes defined within the system, as used by IIASA

IIASA

The International Institute for Applied Systems Analysis is an international research organization located in Laxenburg, near Vienna, in Austria. IIASA conducts interdisciplinary scientific studies on environmental, economic, technological and social issues in the context of human dimensions of...

, are:

1. Polar desert
   Polar desert
   Polar deserts are areas with annual precipitation less than 250 millimeters and a mean temperature during the warmest month of less than 10°C and in the coldest month has a mean temperature of 56degress Polar deserts on Earth cover nearly 5 million square kilometers and are mostly hard bedrock or...
   
   
2. Subpolar dry tundra
   Tundra
   In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word tūndâr "uplands," "treeless mountain tract." There are three types of tundra: Arctic tundra, alpine...
   
   
3. Subpolar moist tundra
4. Subpolar wet tundra
5. Subpolar rain tundra
6. Boreal desert
   Desert
   A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
   
   
7. Boreal dry scrub
8. Boreal moist forest
   Forest
   A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
   
   
9. Boreal wet forest
10. Boreal rain forest
11. Cool temperate desert
12. Cool temperate desert scrub
13. Cool temperate steppe
    Steppe
    In physical geography, steppe is an ecoregion, in the montane grasslands and shrublands and temperate grasslands, savannas, and shrublands biomes, characterized by grassland plains without trees apart from those near rivers and lakes...
    
    
14. Cool temperate moist forest
15. Cool temperate wet forest
16. Cool temperate rain forest
17. Warm temperate desert
18. Warm temperate desert scrub
19. Warm temperate thorn scrub
20. Warm temperate dry forest
21. Warm temperate moist forest
22. Warm temperate wet forest
23. Warm temperate rain forest
24. Subtropical desert
25. Subtropical desert scrub
26. Subtropical thorn woodland
27. Subtropical dry forest
28. Subtropical moist forest
29. Subtropical wet forest
30. Subtropical rain forest
31. Tropical desert
32. Tropical desert scrub
33. Tropical thorn woodland
34. Tropical very dry forest
35. Tropical dry forest
36. Tropical moist forest
37. Tropical wet forest
38. Tropical rain forest

See also

• Andrew Delmar Hopkins
  Andrew Delmar Hopkins
  Andrew Delmar Hopkins was an American entomologist in the late 19th and early 20th centuries, becoming head entomologist for the U.S. Department of Agriculture in 1904. His research was primarily on bark beetle population dynamics and impacts, and he also developed the Law of Bioclimatics....
  
  
• Biome
  Biome
  Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a...
  
  
• Ecoregion
  Ecoregion
  An ecoregion , sometimes called a bioregion, is an ecologically and geographically defined area that is smaller than an ecozone and larger than an ecosystem. Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural...
  
  
• Holdridge life zones in Guatemala
  Holdridge life zones in Guatemala
  There are 14 Holdridge life zones in Guatemala:...
  
  
• Köppen climate classification
  Köppen climate classification
  The Köppen climate classification is one of the most widely used climate classification systems. It was first published by Crimea German climatologist Wladimir Köppen in 1884, with several later modifications by Köppen himself, notably in 1918 and 1936...
  
  
• Life zone
  Life zone
  The Life Zone concept was developed by C. Hart Merriam in 1889 as a means of describing areas with similar plant and animal communities. Merriam observed that the changes in these communities with an increase in latitude at a constant elevation are similar to the changes seen with an increase in...