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Saturday, 10 March 2007
Tropical Grassland Overview
Topic: Tropical Grassland
Tropical grasslands, also known as Savannahs, are characterized by their fire-tolerant C4 grasses in fine soils. They occur between 10-25 degrees latitude in the northern and southern hemispheres where the hot climate allows fires to run rampant during the dry season. Woody plants have a longer growth period than grasses, so grasses predominate in these fire-prone areas because they can easily grow back. Various drought-adapted, fire-resilient trees are also scattered throughout the grassland. Some adaptations grasses have include a dense, shallow root system and C4 photosynthesis. The dense, shallow roots can quickly absorb top water when it falls. In addition to this, the plant meristem is underground so it cannot be harmed by fire. C4 photosynthesis is a system the grass uses to produce energy more efficiently by physically separating the location of respiration in the leaf.

Climate: The climate is warm with seasonal rainfall. Most grasses pollinate in the wet season. This is when fire is less likely to destroy young plants. Their productivity is limited by water. There is roughly 250-1600mm precipitation annually, particularly during the wet summer months. Generally there are 3 months of low precipitation, which constitute the dry season. Some woody species may lose their leaves in the dry season to conserve water loss.

Soil: Fine soils are characteristic of grassland because it retains the water near the surface where it is readily available to grasses. Also the soil is nutrient poor, so Nitrogen producers have a competitive advantage over other plants. In the grassland there are four main types of soils: Oxisols, Alfisols, Entisols, and Vertisols. Oxisols are red soils due to their high iron content; they are finer and wetter than others. Alfisols contain higher quartz content than Oxisols, due to a combination of calcification and lateralization, and therefore they are grainier. Entisols are sandy soils which are less fertile than the rest because they have low phosphorous content. Vertisol is highly acidic and has the consistency of clay so it will crack in the dry months.

Geographic Distribution: Grasslands can form on any continent between 10-12 degrees latitude where they can be maintained by fire. In South America the largest grassland area is between southern Brazil and Paraguay. In Central America grasslands are primarily human-made. Slash-and-burn techniques tear down tropical forests. Infertile soils that once were tropical forests contribute to grasslands because with slow growth rates by trees, there is an increased probability that fire will reset the growth,thus making the fast growth rate of grasses advantageous. Southeast Asia and inland Australia also have large grassland where dry winter months make it difficult for large trees to grow. Africa has the most extensive savannah, which has been made popular by pictures of the Serengeti.

Fauna: Large grazers and browsers are the predominant feature of the grassland. Typical examples include: giraffes, elephants, zebra and kangaroo. They have extensive regional migration patterns following the grasses and rain. Of the non-migratory species, termites are a keystone element. They decompose cellulose and move nutrients throughout the soil. On a larger scale, vultures eat carrion and recycle nutrients back into the food web.




Posted by planet/bruinsavannahs at 12:01 AM PST
Updated: Thursday, 15 March 2007 12:40 AM PDT
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Friday, 9 March 2007
Affect of grazing on Tropical Grasslands
Topic: Tropical Grassland

What Is Grazing?

A grazer is a type of animal, usually nomadic, whose diet is composed of grasses shrubs, and other such plant material. Grazers include animals such as cows, goats, and sheep. As you have likely seen for yourself, grazers spend all day wandering around eating plant material?GRAZING.

<http://eclectech.co.uk> <www.cow.gr>

What Role Does Grazing Play in Tropical Grasslands?

Herbivory and grazing are integral parts of the Tropical Grassland (AKA-Savannah) biome, where grasses and woody plants such as trees and shrubs coexist, but compete with one another for space. Historically, grazing by native herbivores at moderate levels in such places as the Serengeti has helped to maintain the balance between grasses and woody plants. How you might ask? The more obvious and direct mechanisms are quite simple. By grazing on the grasses, herbivores help to keep grass populations in check so that the Savannahs don?t become completely overrun with grasses, while at the same time, trampling of small seedlings by larger, and less nimble, herbivores such as elephants help to keep tree and shrub populations at bay as well (Breckle,177).

<www.safisafari.com> <www.tourzambia.com>

Grazing also plays an important role in the hydrologic and nitrogen cycles within Savannah ecosystems. By reducing grass biomass above ground, and subsequently removing transpiring surfaces, grazing helps to conserve soil moisture. The less grass there is transpiring above ground, the less water will be lost from the soil through evapotranspiration, resulting in more water within the soil to be utilized for new plant growth. What does grazing have to do with the Nitrogen cycle in these ecosystems? The answer is in the dung! As the famous children?s book states, ?Everyone Poops,? and herbivores are no exception to the rule. Some of the Nitrogen consumed by herbivores while grazing is released back into the soil through their dung and urine, converting it from an unusable source (in the old grass), into a source that is readily available to new growth (Mcnaughton, 284).

<www.brooklyn.cuny.edu>

Many scientific studies have been conducted to investigate the relative importance of grazing within tropical grassland communities, in fact, these studies have shown that in areas where minimal grazing has occurred, plant productivity and species diversity is significantly smaller than in areas where a moderate amount of grazing has been allowed; productivity as much as doubling in regions where a moderate amount of grazing took place, proving that grazing is an important process in maintaining optimum levels of species diversity and productivity in grassland regions (McNaughton, 698).

When Does Grazing Become a Problem?

Grazing sounds great right? It maintains the balance between grass and woody plant species that make the Tropical Grasslands unique, it helps to conserve moisture within grassland soil, and it aids in the cycling of Nitrogen and other nutrients. However, as is true with most good things, too much can be just as bad, and in some cases worse, than not enough. Though grazing has been a natural part of Savannah ecosystems for hundreds of years, and grass species have coevolved with herbivores to develop coping mechanisms for grazing, the carrying capacities of Savannah ecosystems are not unlimited. Just as studies have shown that productivity and diversity increase from low to moderate levels of grazing, the opposite has been proven from moderate to high levels of grazing. As grazing levels continue to increase past the optimum point (dependent on species of vegetation), grasses are consumed faster than they can reproduce, not only leaving space for woody vegetation to grow in, but also leaving more water and nutrients for that woody vegetation to utilize in its growth. (Vegten, 3). This process in which woody shrubs begin to take over in grassland ecosystems is known as shrub encroachment, and is becoming a more and more prevalent problem in areas where higher than optimum levels of grazing are maintained over long periods of time. In what areas has bush encroachment become a threat? Areas of prolonged, domestic, cattle grazing. We only have ourselves to blame.


Posted by planet/bruinsavannahs at 12:01 AM PST
Updated: Wednesday, 14 March 2007 2:06 AM PDT
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Thursday, 8 March 2007
Deciduous Forest Overview
Topic: Tropical Grassland

Temperate Deciduous Forests are easily recognized by their-broad leafed trees that become barren in the winter. This is due to the annual cycle of snowy winters and hot summers in this climate. Dropping leaves is an adaptation against freezing in the winter, however, these plants need a sufficiently long growth period of at least 4 months to grow back their leaves and make up for energy spent maintaining themselves in the winter. During the winter, plants may also go through the process of hardening to tolerate lower temperatures without sustaining damage. They do this by stabilizing membranes and increasing protoplasm viscosity. Therefore, these forests can also be known as hardwood forests.

Climate: The climate is influenced by the ocean. This stabilizes the temperature due to water's high the heat of vaporization. It also allows more moisture into the climate causing an extended growth season as well as heavy winter snows. The growing season lasts roughly six months between the winter frosts. There is typically 800-1400mm precipitation annually, gradually increasing closer to the equator.

Geographic Distribution: The deciduous forests transition into grassy steppe in more arid regions closer to the equator and boreal forests further from it. They generally occur in the holoarrctic region, with the exception of southern Chile, and the southern tip of New Zealand. The largest geographic areas of deciduous forest are the China/Japan region, Eastern United States and Central-Western Europe.

Soil: The deciduous forests' soil is very dark with a high organic content, called humus. It can either be the consistency of clay or sponge. The clayey type is called Ultisol. It is waterlogged and highly anaerobic due to a highly under-decomposed content. The other type is Alfisol, which has a low nutrient content because winter water remains in the soil and turns it acidic. Most nutrient cycling occurs through litterfall. Some flora, however, do not drop their leaves, but instead hold on to them in the winter to prevent herbivory from hungry browsers. These plants are called marcescents.

Fauna: Omnivores are the most noticed animal types. They survive principally by foraging, but they can store high caloric content with protein intake for surviving the winter months. Examples include bears, raccoons and jay birds. Insects, however, are the most abundant animal. They are the primary consumer of plants, particularly in the spring when sprouts are non-woody. Trees and shrubs produce defensive chemical compounds to deter foragers away from them.


Posted by planet/bruinsavannahs at 12:01 AM PST
Updated: Thursday, 15 March 2007 12:52 AM PDT
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CASE STUDY: THE CERRADO
Topic: Tropical Grassland
WHAT IS THE CERRADO?The Cerrado region in South America makes up the largest savanna on the continent as well as one of the most biologically diverse savannas in the world. This savanna, which covers an area of 740,100 square miles (1,916,900 square kilometers), has over 10,000 species of vascular plants as well 180 species of reptiles, 113 of amphibians, 837 of birds and 195 of mammals.
http://www.biodiversityhotspots.org/xp/Hotspots/cerrado/impacts.xml

HOW IS THE CERRADO USED?
Until the 1960?s the Cerrado region was relatively unused for agriculture because of its unusable soil, however when the Southeast region of Brazil began to develop into a more urban area the agriculture was forced west into the Cerrado. Since that time Brazil has tried to invigorate the agriculture in the Cerrado, at the expense of biodiversity, by expanding farming and cattle production. Today, Cerrado produces about 70% of the cattle for the country and through the help of irrigation and soil improving techniques it has become a larger production center for grains. In 2000, the Cerrado region was responsible for 35 percent of all crop production in Brazil. Currently, 58 percent of Brazil's total soy production comes from the Cerrado.(Biodiversity Hotspot) In addition to being threatened by the single-crop plantations, Cerrado is also having part of its vegetation burned for charcoal.
http://www.biodiversityhotspots.org/xp/Hotspots/cerrado/impacts.xml

HOW MUCH IS LEFT?
About 67% of the Cerrado region has been converted or modified in a major way for the sake of agriculture and cattle. However, only about 1% has been protected by conservation in parks and reserves. In addition to the growing agriculture business in the Cerrado, the colonization of the states in the intact Cerrado regions will have a great impact. It is estimated that only 23.1% of the original vegetation is still intact today.

http://www.biodiversityhotspots.org/xp/Hotspots/cerrado/impacts.xml http://www.conservation.org.br/onde/cerrado/

Biodiversity Hotspot


Posted by planet/bruinsavannahs at 12:01 AM PST
Updated: Wednesday, 14 March 2007 9:35 PM PDT
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