To Complement Lectures and Discussions
on this Topic in SSC 701
Images and Links to Other Sites
To Complement Lectures and Discussions
on this Topic in SSC 701
Acid savannas occupy large areas of South America and Africa. In the Central
Plateau of Brazil they are known as "Cerrados" and a specific nomenclature
has been developed that is based on the density and size of trees. Cerrados
with a dense tree cover are called "Cerradão".
As tree density decreases they become "cerrado",
"campo sujo", and "campo
limpo". There are various theories on origins of the unique vegetation
( note tortuosity of tree trunks) in this ecosystem. For a review of these theories
and relationships with soil properties check out the articles by Lopes and Cox
(Agron. J. 69:828-831 (1977) & Soil Sci. Soc. Am. J. 41:742-747
(1977)). During the long dry season savannas are subject to widespread burning,
sometimes man-induced to promote growth of new forage when the rainy season
begins. Because of their relatively flat topography, large areas of the "cerrados"
have been cleared for mechanized production. An example is this
region near Dourados.
The Brazilian Agricultural Research Agency (EMBRAPA) has a research center that focuses specifically on this ecosystem. This provides you a link to EMBRAPA's home page.
The Llanos of Colombia are another example of savannas that are predominated
by acid soils. During periods of high rainfall in the wet season they may become
temporarily flooded. Contrast
this with the dry season.
Savannas, such as this one in Australia, are not associated with acid soils.
Another example is the region near Guanacaste,
along the Pacific coast of Costa Rica.
Semiarid tropics comprise large areas of Africa, India, Australia, and portions
of Mexico and Northeastern Brazil. The dry season lasts 6-9 months and the soils
are dry almost half of the year. Vegetation
includes sparse, thorny trees and shrubs, and grasses. The Sahel region in equatorial
Africa, which forms the southern border to the Sahara
Desert is subject to considerable wind erosion. Many of these sandy soils
develop surface crusts which limit
infiltration during the rains and increases runoff.
Land tenure and management in the Sahel is often administrated by village chiefs
in settings such as this in Burkina Faso. Land is allocated to heads of households,
remains in the lineage and should not be sold. Grazing animals are entrusted
to nomadic herders and are excluded from cultivated lands during the growing
season. Set aside grazing land is often communal, as are cultivated lands after
harvest. For further details, see TropSoils Bulletin No. 91-04 (1991),
Soil Management CRSP, North Carolina State University, Raleigh, NC.
The humid tropics includes a significant portion of Central America and large
areas of South America, Africa and Asia. Rainfall exceeds potential evapotranspiration
in most months and vegetation consists of evergreen
tropical rainforests. The Amazon
Basin has extensive areas wherein shifting
cultivation continues to be the main agricultural system. As cultivators
abandon cleared land for new areas, land reverts to secondary forest vegetation.
These are locally known as "capoeiras" or "purmas". In young
"capoeiras" cultivators will still harvest the plantains, which
disappear with increasing time of fallow.
Population has continued to grow in the Amazon and today there are several cities with over 1 million people, such as Belem and Manaus. Accessibility to the region has increased with construction roads through the region. This is illustrated with a satellite photo of the Manaus region, where the west-to-east flowing Amazon River meets the dark-waters of the Rio Negro flowing north-to-south. Note land clearing along the roads a) north of Manaus, b) along the peninsula between the two rivers, and c) south of Manaus. Improved transportation facilitates mining and logging activities and the development of agricultural colonization projects. Colonization projects in the State of Rondonia have resulted in large influxes of landless people from South Brazil during the last decade. The satellite photo shows the clearing which has occurred along the grid work of roads in such a project. As human activity in the region grows there is increasing concern about the loss of biodiversity, the impact of burning on global climate change, and land degradation.
Although the predictions can sometimes sound devastating, it is helpful to remember that land clearing in North Carolina began centuries ago by the same process. Compare historical pictures of our mountains with their appearance today.
Additional information on these issues is available by browsing Web sites for
the Brazilian National Research Council's Institute for Amazonian Research (INPA),
EMBRAPA's Agroforestry Research Center (CPAA),
and Brazil's National Space Institute (INPE).
The latter provides good data, based on satellite imagery, about deforestation,
demographics, agriculture and natural resources in the Brazilian Amazon.You
may also wish to check the following:
World Conservation Monitoring Centre
Alternatives
to Slash and Burn Programme
Food and Agriculture Organization of the U.N.
Steeplands comprise major areas of Asia, Central America and the Pacific Coast
of South America. These are areas above 900m elevation where temperatures can
be quite cold. Rainfall patterns are diverse across short distances due to "rain
shadow" effects. Consequently vegetation ranges from desert,
to tundra-like, to cold-tolerant
crops. They can be densely populated and have considerable agricultural
activity. Erosion can be a major problem in these areas, as noted in this
picture near Quito, Ecuador. Effective control is exemplified by the use
of terraces in Asia.
There are a variety of sites which you can view tropical weather. Some even
provide a time series of still frames that illustrate movement along the tropical
convergence zone. The following are a few you may wish to try:
INPE - South American
satellite images
Weather at Yahoo - global
coverage
The Weather Underground -
world coverage
Hawaii
Meteorology - Pacific coverage
Some you may not yet know - but there are many more
Rubber
- young plantation, established
plantation, and tapping panel
on tree trunk.
Oil
Palm - a plantation in Malaysia
and a closer look at the plant.
Cacao
- a plantation and a closer look at
the fruit. The pulp is separated
from the seed and the seed is fermented before processing into chocolate
Theobroma grandiflora - native to the Amazon and closely related
to cacao, but current commercial interest is in the pulp rather than the seed.
Known as "cupuaçu" in Brazil.
Black
Pepper - Fusarium is a big problem for this plant.
It commonly is supported by large wooden stakes. Here is a close-up of the fruit.
Paullinia
cupana - native to the Amazon and known as "guarana"
in Brazil. A bushy, vine-like plant.
Interest is in the black seed. Chemical
analyses indicates that caffeine content is higher than in coffee.
Brazil
Nut - it is hard to see but there are brown
fruits at the top of the tree canopy.
Pashion Fruit
Star Fruit
Banana
Coconut
Peach Palm - for heart-of-palm, oil, waxes, animal rations, edible
fruit.
Anona muricata - grown throughout Latin America; "guanabana"
in Spanish, "graviola" in Portuguese.
Tea
- leaf harvest on a plantation in
Kenya.
Jacaranda - one of several hardwoods that do well in the Amazon.
Coca
- in association with citrus in Bolivia;
drying harvested leaves to sell.
The Consultative Group for International Agricultural Research (CGIAR) supports a network of sixteen international agricultural research centers. Through this link to CGIAR, you can access pages for each of these centers. There is interesting information on the centers' pages about both commodities and various tropical ecosystems.
Last Modified on October 24, 1999
