Images © by James L. Reveal, Norton-Brown Herbarium, University of Maryland, unless otherwise credited.

Low montane rain forest edge, Cerro Pierre, Panama (above)
Montane rain forest, Panama (below, right)

---

XV. Tropics

• A. Location: Central America, Caribbean islands, equatorial South America and western Africa, southeastern Asia from India to Malaysia, northern Australia, and many Pacific Islands. Forests cover about seven percent of the earth's surface, half of that is tropical. Restricted to southern Florida in the continental United States.
  B. Features:
  • 1. Vast number of densely spaced trees and enormous diversity of species, sites and sounds.
    2. General lack of seasonality.
    3. Precipitation about 80-160 in (200-400 cm) or more in North America
    4. Mean average temperature is 70-80° F (22-27° C) for most of the region.
    5. Frost and freezing temperates restricted to tropical mountains.
    6. High humidity, narrow temperature fluctuation, uniform day-length; growing season up to 365 days a year.
    7. Soils are geologically old and therefore generally poor in mineral nutrients.
    8. Fires common during dry season, mostly slow burning and not hot.

  C. Vegetation:

  • 1. Multiple layers in the canopy; significant biomass.
    2. Lianas or woody vines and epiphytes (plants that live on other plants) common, many can be parasitic or semi-parasitic.
    3. Usually large smooth leaves with drip points to prevent water from accumulating on the blade.
    4. Extreme diverse array of species in small area
    5. Numerous subcommunities (see XIIa and XIIb below).

  
  

  ---

  
  
  

  High tide at El Real, Panama

  ---

  
  D. Animals:

  • 1. Numerous species of mammals of diversity types: monkey, tapir, panther, sloth, etc.
    2. Many unique kinds of birds (e.g., parrots), home of numerous migratory song birds and water fowl.
    3. Incredible numbers of insects; a single tree can harbor some 30,000 different species.
    4. Relationships between ants and plants are significant evolutionarily.
    5. See this series of papers by Daniel H. Janzen on "Plant Defences against Animals: Introduction; the role of latex in The Rubber Connection; the host specificity of caterpillars on plants in the Amazon, and the Pattern of Chemical Defenses among tropical plants.

  E. History:

  • 1. Much of the tropics in place over last million years although size variable due to changes in sea level.
    2. Rates of speciation high with limited selection pressure (unlike arid areas) so that numerous, distinct but hardly distinguishable species exist to increase diversity.

  
  

  ---

  
  
  

  Soil erosion, Panama

  ---

  
  F. Exploitation:

  • 1. Cutting of forest to create large expanses of grazing land rapidly depleting tropical forests resulting in soil depletion, erosion and changes in local climates. It is estimated that approximate 80 acres a minute of rain forest are disappearing, roughly an area the size of the state of Colorado yearly.
    2. Mining and logging (for lumber and pulp) resulting in forest destruction and pollution, silting, and other water problems.
    3. Introduction of exotic species often resulting in loss of native species. It is estimated that nearly 50 species go extinct each day in the tropics, largely due to human pressures.
    4. There are some efforts, as in Australia where there is a rainforest cabinet timber industry, to study alternative modes of production so as to reduce the need to cut native forests. International support agencies are starting to look at their programs and adjusting them to consider global environmental needs.

  G. Summary:

  • a. Introduction.
    b. Origin.
    c. Environment.
    d. Biota.
    e. Population structure.
    f. Biological productivity.

XVa. Subcommunities of Lowland Tropical Regions:

• A. Rain Forests: Plains or low mountain ranges in tropical regions of the world, almost always at low elevations. Prolonged drought is rare or non-existence, and cold temperature do not occur. Complex forest structure. Numerous species with epiphytes and lianas common.
  B. Evergreen Seasonal Forests: Dry season less than three months; precipitation (about 65 in or 180 cm), dry season mostly less than 4 in (10 cm). Large scattered trees, epiphytes and lianas still common.
  C. Deciduous Seasonal Forests: Dry season about five months, two months when rainfall does not exceed 1 in (2.5 cm). Trees and shrubs in two distinct strata; trees nearly always deciduous and the shrubs evergreen. Lianas and epiphytes are rare.
  D. Tropical Savannas: Large open areas of tropical graminoids and scattered low trees and shrubs. Formed by combination of dry, nutrient poor soils with possibly some influences by climate and human activities, the latter two not well understood. Probably maintained by grazing animals (to Early Holocene) and fire. Savannas in Central America and parts of South America, more common in Africa. Considerable diversity and threat.
  E. Summary of information on savanna:
  • 1. Introduction.
    2. Origin.
    3. Environment.
    4. Biota.
    5. Population structure.
    6. Biological productivity.

---

Tropical Savanna, Nicaragua

---

XVb. Subcommunities of Montane Tropical Regions:

• A. Low Montane Rain Forest: Similar to rain forests but with better soil drainage only trees not as tall. Mostly below 800 ft (250 m) elevation. Epiphytes and lianas common.
  B. Montane Rain Forest: Mid-elevation. Humidity and increased amount precipitation augmented by fog or cloud. Cooler temperatures. Trees shorter, mostly less than 65 ft (20 m), with few lianas and epiphytes. Sub-canopy composed of small shrubs. In most of South and Central America the trees belong to a large number of plant families, but in Mexico, oak (Quercus) and pine (Pinus) more common.
  
  

  
  

  Montane Rain Forest (left) --- Elfin Forest, Panama (right)

  ---

  
  C. High Montane Forest. Lower precipitation. Frost can occur, freezing temperatures on volcanic peaks in Mexico and Central America and the upper reaches of the Sierra Madre Occidental and Sierra Madre Oriental. Common trees include pines and firs (Abies) along with oak. Large shrubs include scrubby alder (Alnus) and maple (Acer). Understory much more tropical.
  D. Elfin Woodlands: Highest elevations of many tropical mountain ranges. Temperature cool but not freezing. Constant cloud cover rather than periodic fog. High humidity. Stunted trees, often gnarled and twisted, with heavy branches due to the occasional strong winds; covered with a multitude of bryophytes and ferns along with numerous flowering epiphytes.
  
  

  ---

  
  
  

  Pármo, Panama

  ---

  
  E. Pármo: High mountain peaks in Central America and Caribbean Islands, common on the Andes of South America. Cool temperatures, frost common. Can be at low elevations in North America and probably formed by strong on-shore winds. Defined by a timberline in South America. Dominated by graminoids, some grasses but sedges (Cyperaceae) and pipeworts (Eriocaulaceae). Columnar, arborescent perennials belonging to sunflower family and lobelia portion of the bellflower family (Campanulaceae) common in the Andes.
  F. Alpine tundra: Top of volcanic peaks in Latin America and in the Andes. Freezing temperatures possible every month. Dominated by graminoids. Limited diversity.

Summary of biomes
Other sites of interest
Biomes of the world: Excellent summary
Biomes: Summary with excellent links
Biomes: A brief review
Extended Lecture Outline notes on biomes: A good review
Critical ecoregions from the Sierra Club
Land Use History of North America: A major review, see in particular the report on the land-use history of the Baltimore-Washington area by Timothy Foresman and his diagram on urbanization from 1792 until 1992
Glossary of ecological terms
The Polar Regions
Alaska Ecoregions
Review of temperate forests
Temperate Forest Factsheet: From World Wildlife Fund
Desert USA: Excellent links
Review of ecosystems
Living Earth
Rainforest database from Living Earth. Many of the articles are valuable sources of information
Tall Grass Prairie of Illinois
Prairie Restoration Links
Facts and statistics on biodiversity
"Effects of climate change on biological diversity in western North America: Losses and Mechanisms" by D.D. Murphy & S.B. Weiss (1992): Technical but most informative
Desert Ecosystems Resource Page Archeology of the Great Basin by Tad Beckman
Rainforest Action Network
An ethnobotanical study of the plants of eastern Peru by Ethan Russo
Rainforests, both temperate and tropical
Rainforest: A photo-essay by Natsuko Utsumi
Amazon Center for Environmental Education and Research: Dr. James A. Duke offers numerous workshops at ACEER on medicinal plants.
Conservation and Planetary Survival: An essay
Smithsonian Tropical Research Institute

Main Terrestrial Biomes page

Last revised: 17 Oct 1997 - Reveal