1 L5: Concepts and Principles of Zoogeography

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Vegetation,the plant cover of the world, is distributed primarily according to climate, especially temperature and rainfall, modified by the nature and history of land and by other things. The distribution of the most important vegetation of the world is shown diagrammatically in Figure. The distribution is zonal, but the vegetation zones are modified, distorted, and interrupted much as the temperature and rainfall zones are.

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Sourcesconsulted (not cited in other reference lists) include E. Mine-Redhead 1954, Proc. Linnean Soc. (London), 165, p. 27, Figure 2 (vegetation map of Africa); anon.

1950, The Australian Environment, 2nd ed., Melbourne, Commonwealth Scientific and Industrial Research Organization, pp. 88-89, Figure 25 (vegetation map of Australia); anon. 1949, Proc. National Inst. Sci. India, 15, p. 358 (map of climate of India in relation to rainfall distribution); Verdoornet al.1945,Plants and Plant Science in Latin America,Waltham, Mass., Chronica Botanica Co., endpaper (vegetation map of South and Central America).

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Tropical rain forests grow around the equator in South America, Africa, and Southeast Asia. They have the highest species diversity per area in the world, containing millions of different species. Even though they cover only a small part of the earth, they house at least one half of all species. The temperature is stable year-round, around 27°C (60° Fahrenheit).

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In the tropics, the most obvious vegetation is rain forest, but it is not uniformly distributed. The largest areas of it are in Amazonian South America, the East Indies, and West Africa, but innumerable smaller strips and patches of it are very widely scattered in the tropics.

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The East Indies or Indies are the lands of South and Southeast Asia. In a more restricted sense, the Indies can be used to refer to the islands of Southeast Asia, especially the Malay Archipelago. The name "Indies" is derived from the River Indus and is used to connote parts of Asia that came under Indian cultural influence (except Vietnam which is in the Chinese cultural sphere).

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The West Indies or Caribbean Basin is a region of the North Atlantic Ocean in the Caribbean that includes the island countries and surrounding waters of three major archipelagoes: the Greater Antilles, the Lesser Antilles and the Lucayan Archipelago.

The region is known as the area running from Florida westward along the Gulf Coast, then south along the Mexican coast through Central America and then eastward across the northern coast of South America. Bermuda is also included within the region even though it is in the west-central Atlantic, due to its common cultural history created by European colonization of the region, and in most of the region by the presence of a significant group of African descent.

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Full-scale rain forest grades into other, poorer types of lowland forest, including tropical deciduous forest; and successive types oflower, wet, evergreen (but usually not coniferous) forest occur at increasing altitudes on wet tropical mountains, until (often at something like 12,000 feet altitude) the forest gives way to grass, and then (often at something like 16,000 feet) the grass gives way to rocks and snow.

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There are also large areas of scrub and savanna in many places in the tropics, including great areas of thorn scrub and seasonally dry grassland in Africa. Sparse desert vegetation covers large areas near the edges of the tropics.

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Temperate forests occur in the next latitude ring (Farther north of the tropics), in North America, northeastern Asia, and Europe. There are four well-defined seasons in this zone including winter. In general, the temperature ranges from -30 to 30°C (-22 to 86° Fahrenheit) and the forests receive 75-150 cm (30-60 inches) of precipitation per year.

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Deciduous (leaf-shedding) trees make up a large proportion of the tree composition in addition to some coniferous trees such as pines and firs. The decaying fallen leaves and moderate temperatures combine to create fertile soil. On average, there are 3-4 tree species per square km. Common tree species are oak, beech, maple, elm, birch, willow, and hickory trees. Common animalsthat live in the forest are squirrels, rabbits, birds, deer, wolves, foxes, and bears. They are adapted to both cold winters and warm summer weather.

Temperate evergreen coniferous forests are found in the northwestern Americas, South Japan, New Zealand, and Northwestern Europe. These forests are also called temperate rain forests because of the large amount of rainfall they see. All this rain creates a moist climate and a long growing season, which results in very large trees.

Evergreen conifers dominate these forests.Common speciesare cedar, cypress, pine, spruce, redwood, and fir. There are still some deciduous trees such as maples and many mosses and ferns — resulting in a Jurassic-looking forest. Common animals roaming the woods are deer, elk, bears, owls, and marmots.

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Farther north, there is first a zone in which deciduous forest and grassland tend to cover alternate, irregular blocks around the mid-latitudes; then a more nearly uniform and continuous zone of northern coniferous forest; and finally a zone of arctic tundra. Southward, the south-temperate parts of Africa, Australia, and South America have complexly mixed vegetations.

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Temperate broadleaf and mixed forests:

Four well-defined seasons in this zone including winter. In general, the temperature ranges from -30 to 30°C (-22 to 86° Fahrenheit) and the forests receive 75-150 cm (30-60 inches) of precipitation per year.

Common tree species are oak, beech, maple, elm, birch, willow, and hickory trees.

Common animals that live in the forest are squirrels, rabbits, birds, deer, wolves, foxes, and bears.

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Boreal forests, also called taiga, are found between 50 and 60 degree of latitude in the sub-Arctic zone. This area contains Siberia, Scandinavia, Alaska, and Canada. Trees are coniferous and evergreen.

There are two seasons here: a short, moist, mildly-warm summer and a long cold dry winter. Temperatures range from -40 to 20°C (-40 to 68° Fahrenheit). Precipitation is usually delivered as snow because it is so cold, 40-100 cm (15-40 inches) each year.

The ground is comprised of a very thin layer of nutrient-poor, acidic soil.

Evergreen conifers with needle leaves that can stand the cold, like pine, fir, and spruce trees, live here.Animals that live in these forests can withstand long periods of cold temperatures and usually have thick fur or other insulation — among them are moose, bears, lynx, wolf, deer, wolverines, caribou, bats, small mammals, and birds.

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Almost all tundras are located in the Northern Hemisphere. Small tundra-like areas do exist in Antarctica in the Southern Hemisphere, but because it is much colder than the Arctic, the ground is always covered with snow and ice. Conditions are not right for a true tundra to form. Average annual temperatures are -70°F (-56°C).

The ground is permanently frozen 10 inches to 3 feet (25 to 100 cm) down so that trees can't grow there. The bare and sometimes rocky ground can only support low growing plants like mosses, heaths, and lichen. In the winter it is cold and dark and in the summer, when the snow and the top layer of permafrost melt, it is very soggy and the tundra is covered with marshes, lakes, bogs and streams that breed thousands of insects and attract many migrating birds.

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The main seasons are winter and summer. Spring and fall are only short periods between winter and summer. The tundra is the world's coldest and driest biomes.

The average annual temperature is -18° F (-28° C). Nights can last for weeks when the sun barely rises during some months in the winter, and the temperature can drop to - 94° F (-70° C). During the summer the sun shines almost 24 hours a day, which is why the Arctic is also called the Land of the Midnight Sun. Summer are usually warm.

Temperatures can get up to 54° F (12° C), but it can get as cold as 37° F (3° C). Average summer temperatures range from 37° to 60°F (3° to 16°C).

The Arctic tundra is also a windy place and winds can blow between 30 to 60 miles (48 to 97 kilometers) per hour. Of the North American, Scandinavian and Russian tundras, the Scandinavian tundra is the warmest, with winter temperatures averaging 18°F (-8°C).

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The earth has existed for two or three or four billion years or more. Simple plants (algae) probably appeared on it more than a billion years ago. Simple, boneless animals probably appeared considerably more than half a billion years ago. The oldest, jawless, fish-like vertebrates appeared perhaps 400 million years ago, but it was still many million years before the first amphibians appeared on land, and many million more before vertebrates were numerous enough on land and left enough known fossils in enough parts of the world to be geographically significant.

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According to Darlington (1957)- The dating of the table is comparatively unimportant.

It does not matter very much whether the Permian was really 200 million years ago or much more or much less. What does matter is the sequence. This sequence of eras, periods, and epochs of the past is the scale on which all the geological and biological events of the time concerned are placed in relation to each other.

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