Agro-Ecological Zones Classification

Agro-ecological classification: Based on length of available growing period (LGP), which is defined as the period (in days) during the year when rainfed available soil moisture supply is greater than half potential evapotranspiration (PET). It includes the period required for evapotranspiration of up to 100 mm of available soil moisture stored in the soil profile. It excludes any time interval with daily mean temperatures less than 5° C.

- Arid: LGP less than 75 days
- Semi-arid: LGP in the range 75 - 180 days
- Subhumid: LGP in the range 180 - 270 days
- Humid: LGP greater than 270 days

Highland tropical areas and temperate regions are defined by their mean monthly temperature.

- Temperate: One or more months with monthly mean temperature, corrected to sea level, below 5° C.
- Tropical highlands: Tropical areas with daily mean temperature during the growing period 5 -20° C.

Some areas of the LGP map appear to indicate available growing period of zero. In some of these areas livestock can be kept through the use of artificial water sources, eg. boreholes, supplimenting the rainfall based LGP. Examples of such areas include the Horn of Africa, parts of southern Africa, central Australia and parts of the Sahel zone

Length of Growing Periods
(click on the map to enlarge selected areas)

Legend

| This map is a Beta version of an FAO Global AEZ product. Click here for Copyright information and further details.

Arid zones: | the areas where the growing period is less than 75 days, too short for reliable rainfed agriculture. The coefficient of variation of the annual rainfalls is high, up to 30%. Abiotic factors, specially rainfall, determine the state of the vegetation. The non-equilibrium theory applies in this environment. The main systems found in these zones are the mobile systems on communal lands. Some cases of ranching are present.
Semi-arid zones: | the growing period of plants is between 75 and 180 days. Progressively, biotic factors such human pressure and the resulting land use define the state of the natural resources. Agricultural areas compete with pastoral lands. The livestock systems are diverse : transhumant and semi-transhumant pastoralism, agro-pastoralism, as well as ranching.
Sub-humid and humid zones: | Environmental interactions of livestock with environment being more or less similar, these two zones have been analysed as a whole. Sub-humid zones: the growing period of plants is between 180 and 270 days. The limitation of stock farming is more the quality than the quantity of pasture available. The systems are also transhumant and semi-transhumant pastoralism, sedentary grassland farming and ranching. Humid zones: with the growing season exceeding 270 days, the natural vegetation is mostly the rainforest. Livestock and grasslands can compete with forest. A part of agriculture is based on tree crop plantations. Agro-pastoralism, ranching and grassland farming are practised.
Temperate and tropical highlands: | Temperate zones: one or more months with monthly mean temperature (corrected to sea level) below 5°C. It includes cold countries as the asiatic steppe areas and the alpine grasslands. Tropical highlands: tropical areas with daily mean temperature during the growing period in the range 5 - 20°C. Temperature is a seasonal limitation to plant growth more than rainfall. All systems ca be found in these zones.

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