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F020 Tropical Lowland Humid Forest Formation
Type Concept Sentence: Tropical Lowland Humid Forest is dominated by broad-leaved evergreen trees, often with multiple complex strata and growth forms in lowland to submontane or premontane elevations with aseasonal to moderately seasonal rainfall and warm temperatures.
Common (Translated Scientific) Name: Tropical Lowland Humid Forest Formation
Colloquial Name: Tropical Lowland Humid Forest
Hierarchy Level: Formation
Type Concept: Tropical Lowland Humid Forest occurs in the humid tropics, often within 10°of the equator, where rainfall is abundant and well-distributed throughout most or much of the year, including both wet evergreen and moist semi-evergreen forest. Elevations range from lowland to submontane or premontane, with ranges from sea level to between 1000 and 1700 m depending on location. Soils are often ancient and deeply weathered, reddish and yellow clays or sands, or more recent soils found on volcanic, colluvial and alluvial deposits. Tree growth forms predominate and are tall, of numerous species, with buttressed bases (in some cases), 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 often exceed 30 m. Evergreenness varies from completely evergreen to semi-evergreen seasonal forests, in which around 25% of the main canopy may be regularly deciduous. The vegetation is often species-rich, often lacking dominants, with the majority of the tree species of very low abundance.
Diagnostic Characteristics: Tropical Lowland Humid Forest is dominated by meso- to megaphyll, broad-leaved evergreen trees (up to 25% deciduous trees), with a complex multi-layer structure, often exceeding 30 m in height. Climates are consistently warm (seasonal daily temperatures with minimal variation), and annual rainfall is relatively aseasonal and typically >100 cm, with any given month rarely <60 mm.
Rationale for Nominal Species or Physiognomic Features: No Data Available
Classification Comments: Heath forests are a striking variant within this formation, as described by Richards (1996) and Whitmore (1998). They occur on podsolized soils developed from siliceous sand, either coastal alluvium or weathered sandstones. Although typically found in a rainforest climate and retaining basic growth forms characteristic of 1.A.2 ~Tropical Lowland Humid Forest Formation (F020)$$, the nutrient-poor, acidic conditions produce a strikingly distinct physiognomy. Here are found dense, often pole-sized trees, a stronger predominance of microphylls over mesophylls, with some sclerophylly, and woody climbers that are more often slender. The most extensive heath forests are found in the upper reaches of the Rio Negro and Rio Orinoco of South America, also in Guyana (wallaba forests of Eperua falcata), coastal forests of southeastern Madagascar, Gabon, Cameroon and Ivory Coast, and in Kalimantan, Sarawak and Brunei in Borneo (referred to as kerangas), and parts of Malaya (Whitmore 1998).
Tropical montane forests may resemble heath forests to some degree (Whitmore 1998).
Tropical monsoon forests are sometimes grouped with Tropical Lowland Humid Forest as "tropical moist forest" (Whitmore 1998), but by and large, they are included with 1.A.1 ~Tropical Dry Forest & Woodland Formation (F003)$$. Further review is needed of the transition between monsoon forests and humid forests or rainforests.
Tropical montane forests may resemble heath forests to some degree (Whitmore 1998).
Tropical monsoon forests are sometimes grouped with Tropical Lowland Humid Forest as "tropical moist forest" (Whitmore 1998), but by and large, they are included with 1.A.1 ~Tropical Dry Forest & Woodland Formation (F003)$$. Further review is needed of the transition between monsoon forests and humid forests or rainforests.
Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Tropical Lowland Humid Forest is a dense, multi-layered forest, with broad-leaved evergreen trees that can exceed 45 m in height. The tree layer is minimally divided into a top stratum with giant emergent trees, over a main stratum between 25 and 35 m tall, under which a stratum of shorter trees between 10 and 25 m occurs. Ground vegetation may be sparse, commonly with small trees (treelets). Herbs may be patchy. Individual trees may be deciduous or semi-deciduous, but overall comprise <25% of the main stratum. Evergreenness varies from completely evergreen to evergreen seasonal forest (which is mainly evergreen but individual trees may lose their leaves) to semi-evergreen seasonal forest (in which up to about 25% of the main canopy may be deciduous) (Richards 1996). Whitmore (1998) notes the following features: buttresses are common, cauliflory and ramiflory are occasional to common, pinnate leaves are frequent, leaf blades of mesophyll size predominate, big woody climbers (mostly free-hanging) are frequent to abundant, bole climbers, shade and sun epiphytes are occasional to frequent, and bryophytes are rare (Table 1). These characteristics are lost as forests become drier or as elevation increases.
Table 1. Characters used to distinguish Tropical Lowland Humid Forest from Tropical Montane Humid Forest (after Whitmore (1998), Table 2.2).
Table 1. Characters used to distinguish Tropical Lowland Humid Forest from Tropical Montane Humid Forest (after Whitmore (1998), Table 2.2).
| Formation Criteria | Tropical Lowland Humid Forest | Tropical Montane Humid Forest |
| Canopy height | 25-45 m | 1.5-33 m |
| Emergent trees | Characteristic, to 60 (80) m tall | Often to usually absent, to 37 m tall |
| Pinnate leaves | Frequent | Rare to very rare |
| Principle leaf size class of woody plants | Mesophyll | Mesophyll or microphyll |
| Buttresses | Usually frequent and large | Uncommon, small or absent |
| Cauliflory | Frequent | Rare to absent |
| Big woody climbers | Abundant | Usually none |
| Bole climbers | Often abundant | Very few, frequent to abundant |
| Vascular epiphytes | Frequent | Frequent to abundant |
| Nonvascular epiphytes | Occasional | Occasional to abundant |
Floristics: No Data Available
Dynamics: No Data Available
Environmental Description: Climate: Tropical Lowland Humid Forest (including semi-evergreen rainforest) occurs in aseasonal, humid climates where water stress is low to absent, with no regular annual dry season (Whitmore 1998). In general, a tropical rainforest climate can be defined as one with monthly mean temperatures of at least 18°C throughout the year, and an annual rainfall of at least 170 cm (and usually above 200 cm) and either no dry season or a short one of fewer than 4 consecutive months with <10 cm rainfall (Richards 1996, Whitmore 1998).
African rainforests are primarily semi-evergreen (where deciduous trees may comprise up to 25% of the main canopy), as are Australian rainforests, and various parts of other regional rainforest blocks (Whitmore 1998).
Soil/substrate/hydrology: These forests generally occur from sea level to approximately 1200 m elevation, but the boundary between lowland and montane forests occurs at different elevations depending on the "Massenerhebung effect" (Collins 1990, Richards 1996). This is a phenomenon whereby large mountains and the central parts of large ranges are warmer at given elevations than small mountains and outlying spurs. Thus Collins (1990) mapped the boundaries in the Caribbean, Central America, Madagascar, Australia and Southeast Asia at 910 m, whereas in West Africa the boundary was set at 1200 m, in New Guinea at 1400 m and in South America at 1800 m.
Soils are often ancient and deeply weathered, with little organic darkening of the topsoil and with bright reddish or yellowish colors throughout the subsoil. Few of the original rock minerals remain in the upper horizon. Organic content may vary. Soils are often clay-like, but weathered sands also occur. Other more recent soils include those found on recent volcanic deposits, colluvial and alluvial soils (Richards 1996).
African rainforests are primarily semi-evergreen (where deciduous trees may comprise up to 25% of the main canopy), as are Australian rainforests, and various parts of other regional rainforest blocks (Whitmore 1998).
Soil/substrate/hydrology: These forests generally occur from sea level to approximately 1200 m elevation, but the boundary between lowland and montane forests occurs at different elevations depending on the "Massenerhebung effect" (Collins 1990, Richards 1996). This is a phenomenon whereby large mountains and the central parts of large ranges are warmer at given elevations than small mountains and outlying spurs. Thus Collins (1990) mapped the boundaries in the Caribbean, Central America, Madagascar, Australia and Southeast Asia at 910 m, whereas in West Africa the boundary was set at 1200 m, in New Guinea at 1400 m and in South America at 1800 m.
Soils are often ancient and deeply weathered, with little organic darkening of the topsoil and with bright reddish or yellowish colors throughout the subsoil. Few of the original rock minerals remain in the upper horizon. Organic content may vary. Soils are often clay-like, but weathered sands also occur. Other more recent soils include those found on recent volcanic deposits, colluvial and alluvial soils (Richards 1996).
Geographic Range: Tropical Lowland Humid Forest is concentrated around the equator, between the Tropic of Cancer (23°N latitude) and Tropic of Capricorn (23°S latitude). It is found in three major regions: South and Central America; Africa (west, central and interior) and Madagascar; and the Indo-Asian Pacific (India, Southeast Asia, Indonesia, New Guinea, Pacific Islands, and northeastern Australia). In the United States, it is found in Hawaii and in several territories, including Puerto Rico and many of its Pacific island territories.
Nations: AS,AU,FM,GU,MP,MX,PR,PW,US,WS
States/Provinces: No Data Available
Plot Analysis Summary:
http://vegbank.org/natureserve/ELEMENT_GLOBAL.2.860256
Confidence Level: High
Confidence Level Comments: No Data Available
Grank: GNR
Greasons: No Data Available
| Type | Name | Database Code | Classification Code |
|---|---|---|---|
| Class | 1 Forest & Woodland Class | C01 | 1 |
| Subclass | 1.A Tropical Forest & Woodland Subclass | S17 | 1.A |
| Formation | 1.A.2 Tropical Lowland Humid Forest Formation | F020 | 1.A.2 |
| Division | 1.A.2.Eg Caribbean-Mesoamerican Lowland Humid Forest Division | D091 | 1.A.2.Eg |
| Division | 1.A.2.Oa Polynesian Lowland Humid Forest Division | D066 | 1.A.2.Oa |
Concept Lineage: No Data Available
Predecessors: No Data Available
Obsolete Names: No Data Available
Obsolete Parents: No Data Available
Synonomy: = Lowland tropical rain forest: biome-type 1 (Whittaker 1975)
= Tropical Rain Forest (Richards 1996)
> Tropical heath forest (Whitmore 1998) [Heath forests occur on podsolized soils developed from siliceous sand, either coastal alluvium or weathered sandstones. The nutrient-poor, acidic conditions produce a strikingly different physiognomy of dense, often pole-sized trees, stronger predominance of microphylls over mesophylls, with some sclerophylly. Woody climbers are more often slender.]
> Tropical lowland evergreen rain forest (Whitmore 1998) [Whitmore separates out tropical semi-evergreen rainforest, which is here combined at the formation level.]
> Tropical semi-evergreen rain forest (Whitmore 1998) [Whitmore separates out tropical lowland evergreen rainforest, which is here combined at the formation level.]
= Tropical Rain Forest (Richards 1996)
> Tropical heath forest (Whitmore 1998) [Heath forests occur on podsolized soils developed from siliceous sand, either coastal alluvium or weathered sandstones. The nutrient-poor, acidic conditions produce a strikingly different physiognomy of dense, often pole-sized trees, stronger predominance of microphylls over mesophylls, with some sclerophylly. Woody climbers are more often slender.]
> Tropical lowland evergreen rain forest (Whitmore 1998) [Whitmore separates out tropical semi-evergreen rainforest, which is here combined at the formation level.]
> Tropical semi-evergreen rain forest (Whitmore 1998) [Whitmore separates out tropical lowland evergreen rainforest, which is here combined at the formation level.]
- Collins, M. 1990. The last rain forests: A world conservation atlas. Oxford University Press, New York.
- 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.
- Richards, P. W. 1996. The tropical rain forest: An ecological study. Second edition. Cambridge University Press, Cambridge, UK. 600 pp.
- Whitmore, T. C. 1998. An introduction to tropical rain forests. Second edition. Oxford University Press, Oxford.
- Whittaker, R. H. 1975. Communities and ecosystems. Second edition. Macmillan Publishing Co., New York. 387 pp.