Print Report
F019 Tropical Lowland Grassland, Savanna & Shrubland Formation
Type Concept Sentence: Tropical Lowland Grassland, Savanna & Shrubland is characterized by a ground layer with a more-or-less continuous grass or graminoid layer, or mixed forb layer that may have up to 80-90% shrub cover and/or typically <40% tree cover, and <8 m tall. Shrubs are predominantly broad-leaved evergreen and deciduous, but sclerophyllous growth forms are also included. Stands are found in warm tropical continental climates, with low or pronounced rainfall seasonality, with either one or two short dry seasons, or one long dry season.
Common (Translated Scientific) Name: Tropical Lowland Grassland, Savanna & Shrubland Formation
Colloquial Name: Tropical Lowland Grassland, Savanna & Shrubland
Hierarchy Level: Formation
Type Concept: Tropical Lowland Grassland, Savanna & Shrubland is characterized by shrubs and herbs with mesomorphic growth forms (including broad-leaved, small-leaved, sclerophyllous, and palm shrubs, and forb and graminoid herbs). Annual precipitation is seasonal to monsoonal and typically varies from 50-150 cm. In the driest climates, the herbaceous cover is annual and/or sparse. Vegetation structure varies from open grasslands, with very few woody growth forms to closed-canopy shrubland. Spatially patchy vegetation structure is typical for this type, especially the savannas with clumped or irregular horizontal canopy spacing and variable height. Neotropical and paleotropical savannas are included here as well as lowland shrublands or scrub, such as the Neotropical Cerrado. Savannas represent the vast majority of the area covered by this type and they are characterized by a layer of perennial herbaceous plants, mainly C4 grasses and sedges, and C3 forbs, with varying degrees of shrubs, and with low trees (< 8 m) ranging up to 40% cover. This type is found widely throughout lowland and montane habitats of the tropical latitudes, from the equator to about 23°N and S (Whittaker 1975, Woodward 2008, Faber-Langendoen et al. 2016).
Diagnostic Characteristics: Shrubs and herbs at least 10% cover, mesomorphic trees <40% cover, and <8 m tall, and the majority of cover is composed of mesomorphic shrub (broad-leaved, sclerophyllous, and rosette shrubs) and herb (forbs and graminoids) growth forms compared to xeromorphic or cryomorphic shrub and herb growth forms. The vegetation structure has irregular horizontal canopy spacing.
Rationale for Nominal Species or Physiognomic Features: No Data Available
Classification Comments: Savanna refers to a type of vegetation where grasses form a complete ground cover but there may also be an upperstory of scattered trees, shrubs, or palms. The word savanna comes from a Carib word for a treeless plain covered with grass (i.e., a grassland). The Spanish adopted the term when they colonized the West Indies, and they introduced it to other western languages. Today, among vegetation scientists, the meaning has changed somewhat: "savanna" refers to a type of vegetation where grasses form a complete ground cover; an upperstory of scattered trees, shrubs, or palms is usual (thus tropical grasslands, with or without scattered trees, are referred to as savannas). The term is mostly reserved to describe tropical vegetation, and the popular image of tropical savanna comes from the African part of the biome, where vast grasslands dotted with umbrella-shaped deciduous trees and thorny shrubs are inhabited by herds of large grazing animals. But it can also include low-statured woody vegetation with a strong graminoid layer, such as the Neotropical cerrado, or scrubby forms of African savanna.
The term savanna has also been applied to vegetation of similar structure in temperate zones, but there the term grassland or prairie is used for non-treed grasslands, and savanna is only used when scattered trees are present (between 10 and 30%); these stands are placed in 1. ~Forest & Woodland Class (C01)$$. Some scientists use the term savanna landscape to describe a group of interrelated grassland, gallery or riparian forest, swamps, and/or marsh vegetation.
Savannas in tropical Asia are most likely "derived" and not natural savannas. This means that they are the result of human activities such as logging, burning, and the grazing of livestock, any or all of which altered tropical dry (or deciduous) forests that once grew in the area. Since they are not considered natural, the tropical savannas of India and Southeast Asia are not described in this report (Woodward 2008).
The Caribbean pine savannas, like other treed savannas, should be placed according to the percent coverage of the tree layer. Where grasses and shrubs overtop low trees ("brush prairie"), the stands are placed here in 2. ~Shrub & Herb Vegetation Class (C02)$$. In the tropics, the separation between the lowland shrubland and grassland and warm semi-desert thorn woodland/shrubland should be guided by the presence of succulents, small-leaved and thorny shrubs and trees, and other xeromorphic growth forms, characteristic of the latter.
Savannas that flood seasonally are common in the tropics, especially in South America (the Llanos, Beni, and Pantanal). The extensive hydrologic network combined with topographic complexities and precipitation gradients cause a complex spatial mosaic of upland and seasonally flooded types that might be challenging to classify, with waterlogged soils grading into drained soils within very short distances.
This type may extend to nearly treeline (3000 m elevation), covering the lower montane region. See description for 2.A.2. ~Tropical Montane Grassland & Shrubland Formation (F017)$$.
The term savanna has also been applied to vegetation of similar structure in temperate zones, but there the term grassland or prairie is used for non-treed grasslands, and savanna is only used when scattered trees are present (between 10 and 30%); these stands are placed in 1. ~Forest & Woodland Class (C01)$$. Some scientists use the term savanna landscape to describe a group of interrelated grassland, gallery or riparian forest, swamps, and/or marsh vegetation.
Savannas in tropical Asia are most likely "derived" and not natural savannas. This means that they are the result of human activities such as logging, burning, and the grazing of livestock, any or all of which altered tropical dry (or deciduous) forests that once grew in the area. Since they are not considered natural, the tropical savannas of India and Southeast Asia are not described in this report (Woodward 2008).
The Caribbean pine savannas, like other treed savannas, should be placed according to the percent coverage of the tree layer. Where grasses and shrubs overtop low trees ("brush prairie"), the stands are placed here in 2. ~Shrub & Herb Vegetation Class (C02)$$. In the tropics, the separation between the lowland shrubland and grassland and warm semi-desert thorn woodland/shrubland should be guided by the presence of succulents, small-leaved and thorny shrubs and trees, and other xeromorphic growth forms, characteristic of the latter.
Savannas that flood seasonally are common in the tropics, especially in South America (the Llanos, Beni, and Pantanal). The extensive hydrologic network combined with topographic complexities and precipitation gradients cause a complex spatial mosaic of upland and seasonally flooded types that might be challenging to classify, with waterlogged soils grading into drained soils within very short distances.
This type may extend to nearly treeline (3000 m elevation), covering the lower montane region. See description for 2.A.2. ~Tropical Montane Grassland & Shrubland Formation (F017)$$.
Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Stands are dominated by any mesomorphic herb or shrub growth form, with or without a layer of nonvascular growth form (i.e., lichen, moss). Mesomorphic shrubs include broad-leaved, sclerophyllous, and palm. Semi-shrubs are typically absent. Mesomorphic herbs include forbs (including flowering forbs and ferns) and graminoids. "Savanna" refers to a type of vegetation where grasses form a complete ground cover; an upperstory of scattered trees, shrubs, or palms is usual. Stands vary widely from regular shrub or herb horizontal stem spacing to irregular, typically with a moderately open shrub layer. There is <40% mesomorphic tree cover, trees are <8 m tall, and the majority of shrub and/or herb growth forms is mesomorphic, typically exceeding 10% cover (but may be as low as 1-10%). Nonvascular and dwarf-shrub growth forms may vary from 0 to 10%, and tree seedlings or saplings may be present at any level of cover, if they are below the predominant heights of the shrubs and herbs. At maturity, dominant shrubs and herbs are typically >0.3 m (sometimes over 5-10 m).
The typical grasses are bunchgrasses, some 2-4 m high. The blades are tough and contain many silica bodies. Savanna grasses use the C4 photosynthetic pathway. In addition to grasses, the herb layer of tropical savannas is often rich in sedges and forbs. Trees of the savannas, with the exception of the huge Adansonia digitata (baobab), are rarely taller than 12 m. Most are only 2-6 m tall. A thick bark often defends savanna trees against fire. Many can sprout from their roots, another survival tactic in the face of frequent burning. In Africa, where grazing by large mammals is a major factor, many woody plants are armed with thorns. These same trees and shrubs are apt to have tiny leaves and very deep taproots. Other growth forms commonly found in tropical savannas include subshrubs and annual forbs and grasses, all well-adapted to strongly seasonal environments. The subshrub dies down at the end of one rainy season and produces new woody stems at the beginning of the next. Two flowering seasons are usual in the Tropical Savanna Biome. Some plants bloom at the very beginning of the rainy season even before their leaves have fully developed. Other species bloom in the middle of the rainy season or towards its end. Ecologists recognize different types of savanna according to the spacing and frequency of trees or other woody plants (Woodward 2008). The typical grasses are bunchgrasses, some 2-4 m high. In addition to grasses, the herb layer of tropical savannas is often rich in sedges and forbs. Many of the forbs are members of the pea or legume family (Woodward 2008).
The typical grasses are bunchgrasses, some 2-4 m high. The blades are tough and contain many silica bodies. Savanna grasses use the C4 photosynthetic pathway. In addition to grasses, the herb layer of tropical savannas is often rich in sedges and forbs. Trees of the savannas, with the exception of the huge Adansonia digitata (baobab), are rarely taller than 12 m. Most are only 2-6 m tall. A thick bark often defends savanna trees against fire. Many can sprout from their roots, another survival tactic in the face of frequent burning. In Africa, where grazing by large mammals is a major factor, many woody plants are armed with thorns. These same trees and shrubs are apt to have tiny leaves and very deep taproots. Other growth forms commonly found in tropical savannas include subshrubs and annual forbs and grasses, all well-adapted to strongly seasonal environments. The subshrub dies down at the end of one rainy season and produces new woody stems at the beginning of the next. Two flowering seasons are usual in the Tropical Savanna Biome. Some plants bloom at the very beginning of the rainy season even before their leaves have fully developed. Other species bloom in the middle of the rainy season or towards its end. Ecologists recognize different types of savanna according to the spacing and frequency of trees or other woody plants (Woodward 2008). The typical grasses are bunchgrasses, some 2-4 m high. In addition to grasses, the herb layer of tropical savannas is often rich in sedges and forbs. Many of the forbs are members of the pea or legume family (Woodward 2008).
Floristics: No Data Available
Dynamics: Natural Disturbances: Fires play a critical role in tropical grasslands and, whereas drought may prevent tree establishment in part of the savanna range, fires may override climatic conditions favorable to tropical woodlands and forests in other parts of the range (Bond et al. 2005). Lightning is the most common source of natural fires, but humans have long played a role in increasing the fire frequency throughout the tropics.
Human Disturbances: Humans have had a long history in shaping tropical savannas. In tropical southeast Asia and India, savannas are most likely derived from human activities such as logging, burning, and the grazing of livestock, any or all of which altered tropical dry (or deciduous) forests that once grew in the area (Woodward 2008). Caribbean pine savannas have a more complicated history, with stands being derived from both natural and human processes.
Human Disturbances: Humans have had a long history in shaping tropical savannas. In tropical southeast Asia and India, savannas are most likely derived from human activities such as logging, burning, and the grazing of livestock, any or all of which altered tropical dry (or deciduous) forests that once grew in the area (Woodward 2008). Caribbean pine savannas have a more complicated history, with stands being derived from both natural and human processes.
Environmental Description: Climate: This formation occurs typically within an annual precipitation range of 100-150 cm, with lower and upper extremes around 40 and 200 cm, respectively. The rainfall is seasonal, with either a short (1-3 months) dry season or a long one (5-7 months). Mean annual temperature is about 22-25°C but can reach 6°C in winter at the edges of the tropical distribution range (e.g., southern limit of Cerrado in Brazil), with very occasional frosts). Even though a close correlation exists between tropical savannas and the Tropical Wet and Dry Climate (Aw in the Koeppen climate classification system), climate does not seem to be the main reason most savannas are found where they are; rather, as Woodward (2008) notes, "repeated burning, low-nutrient soils, iron-rich hardpans close to the surface, and the impacts of large grazing and browsing mammals are also factors in the presence and maintenance of many of the world''s tropical grasslands."
Soil/substrate/hydrology: Tropical savanna usually develops on nutrient-deficient, acidic soils (Oxisols, Ultisols) with aluminum toxicity and pronounced alternation of wet and dry conditions. Soils in humid tropical climates are exposed to high rates of leaching, and the amount of leaching is related to the age of the land surface. Thus, in Brazil and western Africa, the savannas lie on very ancient surfaces that for millions of years have been affected by high temperatures and relatively high amounts of rainfall, whereas over much of eastern and southern Africa, the savannas lie on younger, less leached surfaces, and soils are less acidic (pH = 6.2) and somewhat more fertile. Savannas that flood seasonally are common in the tropics, especially in South America (the Llanos, Beni, and Pantanal). There they occur in a complex spatial mosaic of upland and seasonally flooded types, with waterlogged soils grading into drained soils within very short distances. (Woodward 2008).
Soil/substrate/hydrology: Tropical savanna usually develops on nutrient-deficient, acidic soils (Oxisols, Ultisols) with aluminum toxicity and pronounced alternation of wet and dry conditions. Soils in humid tropical climates are exposed to high rates of leaching, and the amount of leaching is related to the age of the land surface. Thus, in Brazil and western Africa, the savannas lie on very ancient surfaces that for millions of years have been affected by high temperatures and relatively high amounts of rainfall, whereas over much of eastern and southern Africa, the savannas lie on younger, less leached surfaces, and soils are less acidic (pH = 6.2) and somewhat more fertile. Savannas that flood seasonally are common in the tropics, especially in South America (the Llanos, Beni, and Pantanal). There they occur in a complex spatial mosaic of upland and seasonally flooded types, with waterlogged soils grading into drained soils within very short distances. (Woodward 2008).
Geographic Range: This formation type, or biome, is found in northern South America, western and southwestern Amazon Basin, Guiana Shield, Brazilian Shield, Western Africa (Guinea-Congolia/Sudania regional transition zone), sub-Sahel (Sudanian regional center of endemism), the Central African Plateau (Guinea-Congolia/Zambezia regional transition zone and the Zambezian regional center), and Eastern Africa (Somali-Masai regional center of endemism), northern Australia and Indomalaysia. They are typically located poleward of the Tropical Rainforest and Tropical Dry Forest biomes and form a transition between those forests and the deserts of the subtropics. The boundary between forest and savanna is often abrupt.
Nations: AU,BR,BS,CG,CU,ET,FM,GU,KE,MP,MR,MX,MZ,NA,PR,PW,SN,SO,TZ,US,ZA
States/Provinces: No Data Available
Plot Analysis Summary:
http://vegbank.org/natureserve/ELEMENT_GLOBAL.2.860246
Confidence Level: High
Confidence Level Comments: No Data Available
Grank: GNR
Greasons: No Data Available
| Type | Name | Database Code | Classification Code |
|---|---|---|---|
| Class | 2 Shrub & Herb Vegetation Class | C02 | 2 |
| Subclass | 2.A Tropical Grassland, Savanna & Shrubland Subclass | S01 | 2.A |
| Formation | 2.A.1 Tropical Lowland Grassland, Savanna & Shrubland Formation | F019 | 2.A.1 |
| Division | 2.A.1.Ea Caribbean-Mesoamerican Lowland Grassland, Savanna & Shrubland Division | D094 | 2.A.1.Ea |
| Division | 2.A.1.Ol Polynesian Lowland Shrubland, Grassland & Savanna Division | D074 | 2.A.1.Ol |
Concept Lineage: No Data Available
Predecessors: No Data Available
Obsolete Names: No Data Available
Obsolete Parents: No Data Available
Synonomy: = Tropical Savanna Biome (Woodward 2008)
- Faber-Langendoen, D., T. Keeler-Wolf, D. Meidinger, C. Josse, A. Weakley, D. Tart, G. Navarro, B. Hoagland, S. Ponomarenko, J.-P. Saucier, G. Fults, and E. Helmer. 2015c. Classification and description of world formation types. General Technical Report RMRS-GTR-000. USDA Forest Service, Rocky Mountain Research Station, Fort Collins, CO.
- Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys. Second edition. USDA Natural Resources Conservation Service, Washington, DC.
- Woodward, S. 2008. Grassland biomes. Greenwood Press, Westport, CT.