Brief overview
More so than any other use today, people rely on drylands to provide forage for the production of domestic livestock. From cattle, sheep, and goat herds, to horses and camels, drylands support large numbers of domestic animals, which become the source of meat, milk, wool, and leather products for humans.
Map description (Map 5)
This map show the density of livestock, including cattle, buffalo, sheep, goats, horses, mules, donkeys, and pigs. Densities range from less than 5 tropical livestock units (TLUs) to more than 40 TLUs per square kilometer. A tropical livestock unit is the common unit for describing livestock numbers of different species; as a single value this expresses the total amount of livestock present regardless of the specific composition.
Some of the highest livestock densities in the world are in the drylands of Asia, Africa, the Middle East, and South America. Very high densities in drylands (greater than 40 TLUs per square kilometer) are found in India and Pakistan, eastern China, the Sahel, Turkey, and parts of southeastern South America. Livestock can help maintain soil fertility, increase nutrient retention and water-holding capacity, and create a better climate for micro-flora and fauna. If drylands are overgrazed, soil compaction and erosion may follow with a decrease in soil fertility, organic matter, and water-holding capacity.
Map description (Map 6)
The International Livestock Research Institute (ILRI) has prepared this global map of livestock production systems (for the developing world only). ILRI defined these 10 production systems based on whether the systems were livestock only, livestock mixed with irrigated cropland, or livestock mixed with rainfed cropland. Each system is further defined according to agro-ecological zone: arid/semi-arid; humid/subhumid; or temperate/tropical highland. The last category, “other,” includes areas where human and livestock populations are low and where native vegetation is widespread.
In comparing the livestock production systems map with the map of dryland extent, a fairly obvious pattern emerges. Livestock only, rangeland-based systems are most predominant in drylands – in Mexico, southern South America, the Sahel, southern Africa and parts of China. Some important areas of mixed irrigated and mixed rainfed production systems are found in drylands, but are much less extensive.
Soils in drylands
The capacity for drylands to produce forage for livestock is determined, in part, by soil condition. The Global Assessment of Human-Induced Soil Degradation (GLASOD) and, more recently, the Assessment of the Status of Human-Induced Soil Degradation in South and Southeast Asia (ASSOD) represent efforts to qualitatively assess soil degradation (See, “Measuring soil condition”).
GLASOD indicates substantial areas of soil degradation around the world. Globally, approximately 20 percent of the soils in drylands are degraded – 17 percent lightly to moderately degraded; over 2.5 percent strongly to extremely degraded (Table 6). Regionally, the soils in Asia and Africa are the most degraded, approximately 370 million hectares of degraded dryland in Asia; 319 in Africa. Although Asia has more total degradation in its drylands, Africa has more soils in the strong to extremely degraded classes (43.5 million hectares in Asia vs. 74.2 million hectares in Africa).
ASSOD focuses on South and Southeast Asia, including seven countries: China, India, Myanmar, Nepal, Pakistan, Sri Lanka, and Thailand. When analyzed according to aridity zone within these seven countries, more than half of the drylands (approximately 53 percent) have degraded soils, most predominantly in the arid zone. More so than the sub-humid zone, the arid and semi-arid zones include more dryland area in the strong and extremely degraded classes. (Table 7).
Vegetation in drylands
Several indicators based on satellite images and with long-term trends can be used to examine dryland vegetation. These indicators include the Normalized Difference Vegetation Index, Net Primary Productivity, and Rain- Use Efficiency.
Normalized Difference Vegetation Index (NDVI)
The Normalized Difference Vegetation Index is a remote sensing tool used to track global vegetation cover. It is derived from Advanced Very High Resolution Radiometer (AVHRR) data and related to the proportion of photosynthetically-absorbed radiation. This index describes the capacity of vegetation canopies to absorb solar radiation.Various institutions have used NDVI for an array of applications, including the USGS-IGBP Global Land Cover Characterization and the USGS-FAO Map of the World
