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S17 Tropical Forest & Woodland Subclass

The U.S. National
Vegetation Classification
Type Concept Sentence: Tropical forests found at lowland and montane elevations including tropical dry forests, and lowland to montane humid forests (tropical rainforests) and tropical forested wetlands, where frost is essentially absent at sea level.
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Common (Translated Scientific) Name: Tropical Forest & Woodland Subclass
Colloquial Name: Tropical Forest & Woodland
Hierarchy Level: Subclass
Type Concept: Tropical Forest & Woodland varies from dry to humid forests, from sea level to montane elevations, and includes forested wetlands. Tropical dry forest (sometimes called Tropical Dry Forest & Woodland or Tropical Seasonally Dry Forest) range in canopy types, including evergreen, semi-evergreen (needle-leaved or broad-leaved), or largely or wholly deciduous. Tree growth forms predominate and may be species-rich, with micro- to mesophyll leaves, but succulent species may be present. It occurs in humid dry tropical climates with a pronounced dry season, during which some or all of the trees may lose their leaves, or leaves may be moderately small and evergreen sclerophyllous. Canopy heights decrease and canopy coverage tends to decrease as the climate dries until the forests are reduced to open, short-statured (5-15 m) woodlands.

Tropical humid forests (including moist and wet forests) occur in the humid tropics where rainfall varies from abundant and well-distributed throughout the year to somewhat seasonal. Tree growth forms predominate, are tall, often of numerous species, some with buttressed bases, often smooth bark, and evergreen meso- to macrophyll leaves. Also present may be tree ferns, large woody climbers or lianas, and both vascular and nonvascular epiphytes, often of greater diversity than the ground layer. Heights may exceed 30 m. Tropical forested wetlands include swamps and mangroves, where soils are seasonally or permanently saturated to inundated by freshwater or saltwater, with hydrophytic plants and, in the case of mangrove, distinctive hydromorphic growth forms adapted to saline conditions.
Diagnostic Characteristics: Tropical Forest & Woodland is dominated by broad-leaved, often megaphyll, evergreen trees, broad-leaved drought-deciduous or semi-deciduous trees, or small-leaved (micro- to mesophyll evergreen trees). Evergreen needle-leaved trees may occur in association with these other growth forms. Climates are consistently warm (seasonal daily temperatures with minimal variation), and annual rainfall is typically >100 cm.
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: Review of tropical monsoon forests is needed, as they can vary from dry to moist.
Similar NVC Types:
S01 Tropical Grassland, Savanna & Shrubland, note: Where tree cover exceeds 10%, stands are typically placed in 1.A ~Tropical Forest & Woodland Subclass (S17)$$. However, in tropical upland savanna regions, stands may have 40% tree cover, where trees are <8 m tall, tree regeneration is sparse to absent, and there is a substantial graminoid layer.
S06 Warm Desert & Semi-Desert Woodland, Scrub & Grassland, note: Thorn woodlands, with xeromorphic characteristics (aphyllous or very small-leaved trees, with succulents), are placed in this subclass, and rainfall is more typically between 25 and 100 cm.
S15 Temperate & Boreal Forest & Woodland, note: Broad-leaved evergreen trees may be common in warm-temperate forests, comparable to tropical dry forests (i.e., evergreen leaves are typically small), but deciduousness is caused by frost, and types are found where a hard frost occurs annually.
CSC01 Woody Agricultural Vegetation, note: 1.A ~Tropical Forest & Woodland Subclass (S17)$$ long-rotation plantations or woody restoration plantings with an irregular structure and a largely spontaneous ground layer may initially be similar to Woody Agricultural Vegetation (S22) in their early stages of development, especially if planted in rows and the understory is strongly manipulated.
S44 Shrub & Herb Wetland, note:
Physiognomy and Structure: Tropical Dry Forest (typically called Tropical Dry Forest or Tropical Seasonally Dry Forest) range in canopy types, including evergreen, semi-evergreen (needle-leaved or broad-leaved), or largely or wholly deciduous Canopy heights decrease and canopy coverage tends to decrease as the climate dries until the forests are reduced to open, short-statured (5-15 m) woodlands (Whittaker 1975). Tree growth forms predominate, with micro- to mesophyll leaves, but succulent species may be present. They occur in humid dry tropical climates, typically with a pronounced dry season, during which some or all of the trees may lose their leaves, or leaves may be moderately small and evergreen sclerophyllous. Some tropical forests have a more sustained dry period, with less seasonality.

Tropical humid forests (including moist and wet forests) occur in the humid tropics where rainfall varies from abundant and well-distributed throughout the year to somewhat seasonal. Tree growth forms predominate, are tall, often of numerous species, some with buttressed bases, often smooth bark, and evergreen meso- to macrophyll leaves. Also present may be tree ferns, large woody climbers or lianas, and both vascular and nonvascular epiphytes, often of greater diversity than the ground layer. Heights may exceed 30 m (Whittaker 1975).

Tropical forested wetlands include swamps and mangroves, with hydrophytic plants and, in the case of mangrove, distinctive hydromorphic growth forms adapted to saline conditions.
Floristics:
Dynamics: No Data Available
Environmental Description: Climate: In general, the tropical humid forest has a fairly consistent average annual temperature, ranging from 26-27°C, and a more variable daily temperature, with changes up to 5°C. In the tropical dry forest, average annual temperatures range between 20° and 30°C, and daily temperatures change from between 26° to 28°C. At sea level, frost is essentially absent from Tropical Forest & Woodland (Holdridge 1967). Rainfall ranges from 100 to 450 cm (400-180 inches), with the rainfall becoming increasingly more seasonal in tropical dry climates, where the dry season may extend for 4-7 months (Holzman 2008).

Soil/substrate/hydrology: Soils in humid regions are often highly weathered ancient soils with high acidity and low nutrient and organic matter content; however, many tropical forests occur on rich volcanic or limestone soils. The major soil orders in the U.S. system include Oxisols, Ultisols, Inceptisols, and Entisols (Soil Survey Staff 1999) [see Brady and Weil (2002) for comparison of U.S. soil orders with Canadian and FAO systems]. Younger and richer soils are found in alluvial habitats or in areas influenced by ashes from volcanic activity (Holzman 2008).
Geographic Range: Tropical Forest & Woodland is concentrated around the equator with tropical humid forest most common between 0° and 10°N and S latitude, and tropical dry forest between 10° and 23°N and S, with latitudinal limits shaped by frost and drought. Tropical Forest & Woodland is found in three major regions: South and Central America and the Caribbean Islands; Africa (west, central, and interior) and Madagascar; and the Indo-Asian Pacific (India, Southeast Asia, Indonesia, New Guinea, Pacific Islands, and northeastern Australia).
Nations: US
States/Provinces:
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: High
Confidence Level Comments:
Grank: GNR
Greasons:
Name:Database Code:Classification Code:
Class 1 Forest & Woodland C01 1
Subclass 1.A Tropical Forest & Woodland S17 1.A
Formation 1.A.5 Mangrove F006 1.A.5
Formation 1.A.2 Tropical Lowland Humid Forest F020 1.A.2
Formation 1.A.3 Tropical Montane Humid Forest F004 1.A.3
Formation 1.A.4 Tropical Flooded & Swamp Forest F029 1.A.4
Formation 1.A.1 Tropical Dry Forest & Woodland F003 1.A.1
Concept Lineage:
Predecessors:
Obsolete Names:
Obsolete Parents:
Synonomy: = Tropical Forest & Woodland (Holzman 2008)
Concept Author(s): Hierarchy Revisions Working Group, Federal Geographic Data Committee (Faber-Langendoen et al. 2014)
Author of Description: D. Faber-Langendoen and E. Helmer
Acknowledgements:
Version Date: 02Aug2016
References:
  • Brady, N. C., and R. R. Weil. 2002. The nature and properties of soils. Thirteenth edition. Prentice Hall, Upper Saddle River, NJ.
  • 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.
  • Holdridge, L. R. 1967. Life Zone Ecology. Tropical Science Center, San Jose, Costa Rica.
  • Holzman, B. A. 2008. Tropical forest & woodland biomes. Greenwood guide to biomes of the world. S. L. Woodward, general editor. Greenwood Press, Westport, CT.
  • 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.
  • Whittaker, R. H. 1975. Communities and ecosystems. Second edition. Macmillan Publishing Co., New York. 387 pp.