Definitions and distributions

Although the term savanna is believed to have originally come from an Arawak word describing "land which is without trees but with much grass either tall or short" (Oviedo y Valdes, 1535), by the late 1800s it was used to mean "land with both grass and trees". It now refers to land with grass and either scattered trees or an open canopy of trees.

Spanish explorers unfamiliar with the term "sabana" called the grasslands they found around the Orinoco River "llanos", as well as calling Venezuelan and Colombian grasslands by that term. "Cerrado" was used on the higher savannas of the central Brazilian plateau.

Many grassy landscapes and mixed communities of trees, shrubs, and grasses were described as savanna before the middle of the 19th century, when the concept of a tropical savanna climate became established. The Koppen classification system was strongly influenced by effects of temperature and precipitation upon tree growth, and his over-simplified assumptions resulted in a tropical savanna classification concept which resulted in it being considered as a "climatic climax" formation. The common usage meaning to describe vegetation now conflicts with a simplified yet widespread climatic concept meaning. The divergence has sometimes caused areas such as extensive savannas north and south of the Congo and Amazon Rivers to be excluded from mapped savanna categories.

"Barrens" has been used almost interchangeably with savanna in different parts of North America; ecologically related are rock outcrop plant communities although fires are often not important to outcrop communities. Sometimes midwestern savanna were described as "grassland with trees". Different authors have defined the lower limits of savanna tree coverage as 5-10% and upper limits range from 25-80% of an area.

Two factors common to all savanna environments are rainfall variations from year to year, and dry-season fires. Savannas around the world are also dominated by tropical grasses which use the C4 type of photosynthesis. In the Americas, savanna vegetation is similar from Mexico to South America and to the West Indies. In North America nearby trees are subtropical types, ranging from southwestern piñon to southeastern longleaf pine and northern chestnut oak.

Changes in fire management

Savannas are subject to regular fires and the ecosystem appears to be the result of human use of fire. For example Native Americans created the Pre-Columbian savannas of North America by periodic burning where fire-resistant plants were the dominant species. Pine barrens in scattered locations from New Jersey to coastal New England are remnants of these savannas. Aboriginal burning appears to have been responsible for the widespread occurrence of savanna in tropical Australia and New Guinea and savannas in India are a creation of human fire use. The maquis shrub savannas of the Mediterranean region were likewise created and maintained by anthropogenic fire.