More so than any other human use today, grasslands are used for the production of domestic livestock. From cattle, sheep and goat herds, to horses and water buffalo, grasslands support large numbers of domestic animals, which become the source of meat, milk, wool, and leather products for humans.
Grasslands also support large numbers of wild herbivores that depend on grasslands for breeding, migratory, and wintering habitat and share the land with domestic herds.
The following summarizes key findings of the PAGE study regarding the condition of grassland ecosystems, as well as the quality and availability of data.
Conditions and trends
- Although much of the PAGE grassland area does not coincide with mapping units that are degraded according to GLASOD extent and degree classes, nearly 49 percent are lightly to moderately degraded and at least 5 percent are considered strongly to extremely degraded.
- Satellite imagery has greatly expanded our ability to measure grassland vegetation. Promising measures for determining grassland condition are long-term trends in NDVI, NPP, and RUE.
- Trends in RUE provide a potential method of separating vegetation declines due to lack of rainfall from declines associated with degradation. Combining this index with other measures, such as livestock densities, may increase our ability to more accurately
evaluate grassland condition.
- While some grasslands support high livestock densities, association of grassland condition with specific livestock densities must be based in part on information about geographic location and management practices as well as on characteristics of the soil,
vegetation, and wildlife.
Information status and needs
- Soil condition is key to evaluating grassland condition; GLASOD provides the only global database on soil degradation. It is heavily criticized, however, for relying on qualitative data interpreted in different ways and produced at too large a scale for assessing degradation at the national level. ASSOD is an improvement over GLASOD, but its 1:5 million scale is still too coarse on which to base national policies. We need a worldwide digital database of soil degradation at 1:1 million backed up by field reconnaissance.
- To take advantage of improved satellite data for monitoring vegetation change, we need continued evaluation of NPP models, compilation of long-term trends, and further evaluation of the use of additional indicators (such as RUE) in the assessment of grassland ecosystem condition.
- Relationships among meat production, livestock densities, and rangeland condition must be assessed with caution. They require worldwide spatial data that differentiate feedlot from range-fed livestock, identify management practices, and report population levels of all livestock – domestic and wild.
Quality and availability of data
PAGE measures and indicators
Data sources and comments
| Soil degradation
|| Global Assessment of the Status of Human-Induced Soil Degradation (GLASOD), spatial, electronic data at 1:10 million; Soil Degradation Assessment for South and Southeast Asia (ASSOD) at 1:5 million (UNEP 1992 and 1997).
| Vegetation change
|| Global satellite imagery; surface reflectance data from NOAA/AVHRR that provides the Normalized Difference Vegetation Index (NDVI); various models using climate and vegetation data to analyze Net Primary Productivity (NPP); University of Maryland Geography Department’s Global Production Efficiency Model (GLOPEM); Rain-Use Efficiency (RUE) Index using data from rainfall stations to indicate regional trends
(UNEP 1997; Cramer and Field 1999; Prince et al 1998; Goetz et al 1999).
| Livestock densities
|| Spatial, electronic data on livestock populations of the world (Lerner and Matthews 1988); regional spatial coverage of Africa by country and other administrative units from the International Livestock Research Institute (ILRI) (Kruska et al.1995).