Definitions for grasslands vary. Some studies classify grasslands by vegetation while others characterize them by climate, soils, and human use of the ecosystem.
In this study, we define grasslands as terrestrial ecosystems dominated by herbaceous and shrub vegetation and maintained by fire, grazing, drought and/or freezing temperatures. According to this definition, grasslands encompass not only non-woody grasslands but also savannas, woodlands, shrublands, and tundra. This broad definition has allowed PAGE analysts to highlight many of the important goods and services provided by this ecosystem: livestock production as well as grassland biodiversity, carbon storage, and tourism and recreation.
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
- Grasslands cover some 40 percent of the earth’s surface (excluding Greenland and Antarctica).
- Grasslands are found in every region of the world; Sub-Saharan Africa and Asia have the largest total area in grassland, 14.5 and 8.9 million square kilometers respectively.
- Of 136 terrestrial ecoregions identified as outstanding examples of the world’s diverse ecosystems, 35 are grasslands, supporting some of the most important grassland biodiversity in the world today.
- The five countries with the largest grassland area are Australia, the Russian Federation, China, the United States, and Canada.
- The five countries with the highest percentage of grassland area, all in Sub-Saharan Africa, are Benin, Central African Republic, Botswana, Togo, and Somalia.
- Regional data for African herbivores show generally steady long-term population trends within the Serengeti ecosystem. Areas outside the protected area boundaries and with fewer law enforcement activities experienced decreases in densities of already-low wildlife populations. .Of nearly 600 key areas for threatened bird species in the Neotropics, 42 are grasslands; 12 percent of the threatened birds are specific to grasslands.
- Twenty-five of the 145 major watersheds of the world are made up of at least 50 percent grassland. Sub-Saharan Africa has the most extensive grassland watersheds; Europe, the least.
- Grasslands are found most commonly in semi-arid zones (28 percent of the world’s grasslands), followed by humid (23 percent), cold (20 percent), and arid zones (19 percent).
- Human populations are highest in the dry grasslands (arid, semi-arid, and dry sub-humid) of Sub-Saharan Africa followed by Asia. Human populations are lowest in the dry grasslands of Oceania.
- Temperate grasslands, savannas, and shrublands have experienced heavy conversion to agriculture, more so than other grassland types including tropical and subtropical grasslands, savannas, and woodlands.
- Global estimates of grasslands are complicated by diverse definitions of grassland, and variability in the designation of boundaries between land cover types.
- Higher-resolution satellite data, available now and expected to become more accessible within the next few years, could improve the information base. These data, however, will most likely remain expensive to obtain, especially for extensive areas.
- Expansion of our knowledge of grassland condition is hindered by disagreement on the characteristics of a healthy grassland ecosystem and the difficulty of identifying the best methods to determine ecosystem health.
- Various satellite sources primarily from the U.S. and Europe are being perfected to better detect, monitor and analyze fires over time. NASA’s website presents current (1999-2000) fire counts and additional fire information at 4km resolution in monthly intervals but these data are not yet available for general analysis. Studies using these data are required to analyze the long-term effects of frequent fires on grassland systems.
