Holdridge life zones
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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[1]. A basic assumption of the system is that both soil and climax vegetation can be mapped once climate is known[2].
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 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[3].
The indicators incorporated into the system are:
- mean annual biotemperature (logarithmic)
- annual precipitation (logarithmic)
- ratio of annual potential evapotranspiration (PET) to mean total annual precipitation.
Biotemperature is based on the growing season length and temperature. It is measured as the mean of refers to 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'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.
[edit] Classes
The classes defined within the system, as used by IIASA, are:
- Polar desert
- Subpolar dry tundra
- Subpolar moist tundra
- Subpolar wet tundra
- Subpolar rain tundra
- Boreal desert
- Boreal dry scrub
- Boreal moist forest
- Boreal wet forest
- Boreal rain forest
- Cool temperate desert
- Cool temperate desert scrub
- Cool temperate steppe
- Cool temperate moist forest
- Cool temperate wet forest
- Cool temperate rain forest
- Warm temperate desert
- Warm temperate desert scrub
- Warm temperate thorn scrub
- Warm temperate dry forest
- Warm temperate moist forest
- Warm temperate wet forest
- Warm temperate rain forest
- Subtropical desert
- Subtropical desert scrub
- Subtropical thorn woodland
- Subtropical dry forest
- Subtropical moist forest
- Subtropical wet forest
- Subtropical rain forest
- Tropical desert
- Tropical desert scrub
- Tropical thorn woodland
- Tropical very dry forest
- Tropical dry forest
- Tropical moist forest
- Tropical wet forest
- Tropical rain forest
