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S01 Tropical Grassland, Savanna & Shrubland Subclass

The U.S. National
Vegetation Classification
Type Concept Sentence: Tropical Grassland, Savanna & Shrubland is dominated by mesomorphic grasses and shrubs, with or without scattered trees (but trees typically <40% cover), ranging from tropical coastal to inland lowland and montane grasslands and shrublands. Stands are found in warm tropical continental climates, typically from the equator to about 23°N and S latitude, with low or pronounced rainfall seasonality, with either one or two short dry seasons, or one long dry season, but frost virtually absent.
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Common (Translated Scientific) Name: Tropical Grassland, Savanna & Shrubland Subclass
Colloquial Name: Tropical Grassland, Savanna & Shrubland
Hierarchy Level: Subclass
Type Concept: Tropical Grassland, Savanna & Shrubland is dominated by grasses and shrubs, with or without scattered trees. Some occur in climates too dry for forest; others depend on soil conditions or fire, or both, rather than climate. The structure is a single, major grass or shrub stratum, or a mix of the two, with trees typically <10% cover, rarely with bare ground.
Diagnostic Characteristics: Tropical Grassland, Savanna & Shrubland is dominated by grasses and shrubs, with or without scattered trees (which may have up to 40% cover). Some occur in climates too dry for forest; others depend on soil conditions or fire, or both, rather than climate, but frost is typically absent throughout the growing season. The structure is a single, major grass or shrub stratum, or a mix of the two, exceeding 10% cover, rarely with bare ground (Whittaker 1975).
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: Dixon et al. (2014) and others suggest that there may be good ecological reasons to treat upland tropical tree savannas, with up to 40% tree cover, trees <8 m tall, and a substantial graminoid layer, as part of 2. Shrub & Herb Vegetation Class (C02), and we allow for that option here. By contrast, in non-tropical regions, we place tree savannas with woodland and forest.
Similar NVC Types:
S17 Tropical Forest & Woodland, note: Where tree cover exceeds 10%, stands are typically placed in 1.A. ~Tropical Forest & Woodland Subclass (S17)$$. However, in tropical upland savanna regions, stands more typically exceed 40% tree cover, trees are >8 m tall, tree regeneration is abundant, and there is no substantial graminoid layer.
S18 Temperate & Boreal Grassland & Shrubland, note: 2.A ~Tropical Grassland, Savanna & Shrubland Subclass (S01)$$ growth forms have a phenology driven by rain and drought, but not frost.
Physiognomy and Structure: Tropical Grassland, Savanna & Shrubland is dominated by grasses and shrubs, with or without scattered trees (but tree cover <40%). Some occur in climates too dry for forest; others depend on soil conditions or fire, or both, rather than climate. The structure is a single, major grass or shrub stratum, or a mix of the two, exceeding 10% cover, rarely with bare ground (Whittaker 1975). The range of variation in upland formations corresponds to Lowland versus Montane versus Coastal patterns of variation.
Floristics:
Dynamics: No Data Available
Environmental Description: 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, but in all cases frost virtually absent.
Geographic Range: This subclass is found widely throughout lowland and montane upland habitats of the tropical latitudes, from the equator to about 23°N and S.
Nations: US
States/Provinces:
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: High
Confidence Level Comments:
Grank: GNR
Greasons:
Concept Lineage:
Predecessors:
Obsolete Names:
Obsolete Parents:
Synonomy: > Tropical Savanna Biome (Woodward 2008) [Woodward includes upland lowland and montane grassland.]
Concept Author(s): Hierarchy Revisions Working Group, Federal Geographic Data Committee (Faber-Langendoen et al. 2014)
Author of Description: D. Faber-Langendoen
Acknowledgements:
Version Date: 17Oct2014
References:
  • 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.
  • Quinn, J. A. 2008. Arctic and alpine biomes. Greenwood Press, Westport, CT.
  • Whittaker, R. H. 1975. Communities and ecosystems. Second edition. Macmillan Publishing Co., New York. 387 pp.
  • Woodward, S. 2008. Grassland biomes. Greenwood Press, Westport, CT.