Tropics

The tropics are the region of the Earth that lie between the Tropic of Cancer (23.5 degrees north latitude) and the Tropic of Capricorn (23.5 degrees south latitude). This region receives the most intense vertical rays of the sun and is characterized by the presence of a persistent low pressure trough, the Intertropical Convergence Zone (ITCZ). Climate in the region is characterized by high monthly average temperatures (in excess of 18 degrees C throughout the year) and high amounts of rainfall. On the northern and southern edges of the region, the subtropical high pressure brings dry conditions during the winter, and these marginal regions experience [Page 1777]a dry season of up to six months. Due to the high levels of precipitation, soils are highly leached and heavily oxidized. Oxisols are the predominant soil order, with Ultisols and Alfisols occurring on the drier margins of the zone. Due to the heavy leaching, most of the nutrients within these ecosystems are bound within the vegetation.

Due to the high levels of precipitation, the biomes of the tropics have some of the greatest net productivity and biomass of any biome on Earth. Tropical rain forest, tropical deciduous forest, and savanna are the dominant biomes of the region, with nearly every biome represented along the slopes of tall mountains such as the Andes. The tropical forests are highly structured into multiple canopy layers, providing a wide range of niches for species to occupy. Also, because the environments of the tropics were relatively stable throughout the last glacial maxima, species in this region have had sufficient time to become highly specialized and occupy very narrow niches. As a consequence, the tropics have greater biodiversity than higher latitudes, but the specialization of these species renders them sensitive to perturbations to habitat. Tropical deforestation threatens many species with extinction, and occurs in all geographic regions within the tropics. The vast majority of threatened tropical species are stenophagous insects that are often specialized to individual tree species, but larger creatures, such as many primate species within Africa, Madagascar, and Indonesia are threatened by loss of forest habitat as well.

The persistence of extractive activities that threaten tropical habitat are legacies of the colonial and postcolonial periods of development and globalization. The tropics were the site of most of the European colonies during the colonial period, with the high productivity of these regions making them attractive for various plantation crops as well as other primary products such as timber. Western thought had long regarded the tropics as being particular harsh climates. Classical Greek geographers regarded the tropics as the uninhabitable Torrid Zone. Belief in a particularly harsh climate not ideally suited for people persisted into the colonial period and found expression in Environmental Determinism, which asserted that tropical environments caused the people living there to have evolved into lazy and unproductive races, and, by contrast, European races of the temperate climates evolved to be more productive. European colonists employed these racial ideologies as a rationale for the exploitation of these people and environments. Although the colonial model of globalization and development gave way to modernizing discourses meant to bring prosperity to these tropical countries, persistent poverty and power inequalities continue to drive extractive activities in the tropics.

...