 |
|
||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|||||||||||||||||||||||||||||||||||||||||||||||||
|
Tropical Forest and Cotton-Top Tamarin Habitat When most people think of the tropics, they think of lush rain forests and the Amazon. In reality, the tropics consist of a diverse group of ecosystems, from savanna to cloud forest, occurring between the latitudes of the Tropic of Cancer and the Tropic of Capricorn, north and south of the equator. These ecosystems are currently experiencing the highest rates of destruction in the world. We provide general information on the tropical forests of Colombia with particular emphasis on the types of forests inhabited by cotton-top tamarins. Information on coastal forests or mangroves, flooded forests, and shrublands should be obtained from other sources. Forest Ecology Rain Forest Rain forest does not only grow in the tropics, but wherever the climatic conditions are conducive. The Pacific Northwest region of the United States, for example, contains temperate rain forest. Tropical rain forest grows where the mean annual temperature is about 26° C (79° F) and annual rainfall is about 4000 mm. These conditions support high biodiversity, 50-80% of all plant species in just 7% of the Earth’s surface. The world record for species richness occurs in Amazonian Ecuador where 473 tree species were found in a 1-hectare plot of land. The largest remaining areas of tropical rain forest are in Brazil, Congo, Indonesia and Malaysia. The vegetation in tropical rain forests is typically divided into five strata:
Illustration modified from Missouri Botanical Garden
Dry forest and semi-dry forest makes up about 55% of Central American and 22% of South American forests. Large dry forests are also found in Australia, India, Africa, and Madagascar. Dry forests grow wherever the mean annual temperature is above 17°C (63°F) and annual rainfall ranges from 250 to 2000 mm. The length of the dry season varies with distance from the equator, but may be as long as 8 months. Dry forests and savannas actually occur under the same climatic conditions; the difference is due to soil fertility. Dry forests average about half the tree species of wet forests (see table below), however, they still rival forests in temperate climates. Additionally, neighboring dry and wet forests have few species in common. Comparison of dry and wet forests with respect to selected ecosystem properties.
More than 90% of dry forests have been destroyed, and less than 2% of what remains is protected. Because of the climate and forest structure, dry forest is easier to clear for agriculture, the soil is more fertile than that of rain forests, and the land is more suitable for livestock. Dry forest does not produce as much biomass as wet forest, coupled with a high demand for wood products, there is additional pressure on the ecosystem. Dry forests are relatively robust, making habitat restoration a feasible possibility, given the presence of a seed source.
Plants:
Protection of forest ecosystems is an important action, not only to protect the inhabiting plants and animals, but for the many services forests provide to humans. The obvious benefit is the wood products we use on a daily basis. Intact forests add to the economy also, with the development of ecotourism ventures. Forests protect our rivers and lakes by filtering out pollutants that would otherwise drain into the water system. Similarly, forests protect us from flooding by absorbing excess water. Many medicinal products were discovered in forests, including quinine, a malaria treatment, and taxol, a treatment against cancer. Forests are also important to counteract global climate change. Global warming occurs, in part, because of increased emissions of greenhouse gases, which are trapped in the atmosphere. The release of carbon dioxide is a natural process; the global carbon cycle is maintained by all plants, which take in CO2 for photosynthesis. The loss of forest not only means the loss of these “carbon sinks,” but actually releases more CO2 into the atmosphere as trees are cut and then burned. Forests of Colombia and Cotton-top Tamarin Habitat In 1988, and again in 2000, Norman Myers, an ecologist, described "hotspots" as priority areas for conservation, based on the degree of endemism (species that occur nowhere else) and the degree of threat (habitat loss). In cooperation with Conservation International, a non-governmental organization, the 25 most species-rich and most threatened regions were identified as hotspots. Colombia is a hotspot, possessing 45,000-55,000 plant species, second only to Brazil. Colombia has also been described as a "megadiversity" country. This initiative, also by Conservation International, demonstrated that just 12 countries have 70% of the planet's biological diversity. Colombia covers 0.77% of the Earth's land surface, but has almost 10% the plants and animals. Other megadiversity countries include Peru, Mexico, Madagascar, and Indonesia.
The topographic variation and its associated precipitation, in part, explains the richness in fauna and flora. Colombia can be divided into four areas: Andean Highlands: The Andes Mountains divide into three distinct chains, Cordillera Occidental, Cordillera Central, and Cordillera Oriental, in the latter of which, the capital of Bogota is located. Mountain peaks are permanently covered with snow, but a moderate climate in the basins and plateaus allows almost 80% of the human population to live in the Andes. PacificLowlands: The Pacific lowlands are bordered by the Cordillera Occidental and the Pacific Ocean, and have been described as a region of jungle and swamps. Such swampy areas, though unpopular with humans, often hold an astounding array of plants and wildlife. Orinoco/Amazon: The Amazon, east of the Andes, covers three-fifths of Colombia's total area, but is only inhabited by about 2% of the human population. The northern region is described as llanos, or seasonally flooded plains, while the southern region contains tropical rain forest.
World Wildlife Fund and the World Bank completed a separate conservation assessment of Latin America in 1995. They described each ecoregion and ranked them for conservation priorities, ranging from critical to relatively intact. Ecoregions are large areas of relatively uniform climate that harbour a characteristic set of species and ecological communities. The map shows the various ecoregions present in Colombia, with most of the cotton-top tamarin range falling within Sinú Valley Dry Forest and Magdalena/Urabá Moist Forest. The conservation status of each of these regions is critical and endangered, respectively.
National Geographic's Map Machine, in collaboration with ESRI, provides us with a picture of land use in Colombia. When we align this map with an illustration of the threat posed by agriculture to the environment, we see that areas which contain pasture or grazing land are under the highest threat of further forest conversion. Whereas, the inaccessibility of the Andes region keeps the land under low threat. Environmental impact was determined using the following data: cultivation methods, types of crop rotation, use of mineral and organic fertilizers and chemicals, irrigation and drainage, and the number of livestock per unit area of pasture. Responses of the environment to the impact were taken into account during classification.
The historical range of cotton-top tamarins occurs in northwestern Colombia between the Atrato River and the Magdalena River, in the Departments of Atlantico, Sucre, Cordoba, western Bolivar, northwestern Antiquoia, and northeastern Choco, from sea level up to 1500 meters. Previous studies have primarily focused on groups of tamarins in the department of Sucre, in semi-dry forest. Proyecto Tití's current field site is located near Santa Catalina in the department of Bolivar, in a dry forest remnant on a finca, or private ranch, known as "El Ceibal." Both of these forests were found to contain about twice as many plant species as other dry forests in Colombia, and up to three times as many species when compared to some Central American and Caribbean localities. Many of the dry forest remnants, including El Ceibal, are isolated and completely surrounded by areas of cultivation and pasture, which further threatens the maintenance of biodiversity. El Ceibal contains a forested area of approximately 300 hectares. The forest is characterized by many lianas and vines growing through three well-defined layers: the canopy contains trees between 10-25 m in height; the understory contains mostly juvenile trees and thin-stemmed species; the herbaceous layer is less than 1 m tall. Most species partially or fully lose their leaves during the dry season. An inventory of the flowering plants (angiosperms) yielded 412 species in 92 families. Of these, 55 species are consumed by cotton-top tamarins, most of them for their fruit but also for their gums. Equipped with a greater understanding of the forest composition in this region of Colombia, we anticipate successful efforts for reforestation and a secure future for the cotton-top tamarin. Sources
|
|||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||
Dry Forest and Seasonally-Dry Forest
Why do tropical forests hold such high diversity?
Terborgh (1980) compared the bird communities in a tropical and temperate
forest, in the Amazon and in South Carolina, and found the Amazonian
forest included five times more species than that in the United States. He
calls this species packing, and attributes this to historical climate
change. In 1969, Haffer proposed the Refugia Hypothesis to explain the
amazing faunal diversity in the tropics. Dry periods during the
Pleistocene resulted in geographically isolated patches of forest. Such
isolation is one mechanism that can lead to speciation, the evolution of a
new species. Alternating wet and dry periods would increase the need for
animals to develop new adaptations. Others believe that the great
diversity of these "refugia" simply reflect the varying amounts of
fieldwork performed at different sites. Nevertheless, because tropical
forests are so unique in species richness and species endemism (species
that occur nowhere else in the world), they have garnered great concern
for the rate of forest destruction.
Our understanding of fragmentation and species’ requirements is
increasingly reflected in the protection of intact pieces of land, as well
as corridors that connect larger areas, allowing for species dispersal.
Caribbean
Lowlands: The Caribbean lowlands occur north of the Cordillera
Oriental to the Gulf of Urabá. Almost the entire historical range of
cotton-top tamarins falls within the lowlands. This region is also the
second most important in the country for economic activity. Approximately
98% of Caribbean tropical dry forest has disappeared.
