On the basis of climatic and geographical conditions, the earth is usually divided into the following four broad vegetation belts:
This zone is divided into the following two types:
(1) Arctic proper:
This zone occurs around the North Pole and remains covered with ice throughout the year. This zone in fact is Tundra biome and its chief components of vegetation include some algae, annual flowering plants, mosses and lichens.
This is a less defined zone which extends from southern arctic to the northern limits of temperate zone. This region is very cold, contains abundant bogs and has vegetation including small height trees, shrubs and herbs in the months of June and July. Ground vegetation often includes some pteridophvtcs, orchids, insectivorous plants, mosses and lichens.
North Temperate Zone:
This zone extends between 30°N latitude and 55°N latitude and includes following two major zones:
(1) North temperate of the eastern zone:
This zone is further subdivided into the following four zones: (i) Western and central Europe. This zone is demarcated in north by the subarctic and in south by Alps and British Islands. Its forests are dominated by several gymnosperm us tall trees like Pinus, Picea and Abies, and angiosperm us trees like oaks, maple and chestnuts.
Ground vegetation comprises orchids, wild roses, buttercups, Viola, Salvia Dianthus, etc. At high altitudes of this zone trees are replaced by grassy vegetation with some herbaceous flowering plants, (ii) Mediterranean. This zone extends between 30’N and 40°N latitudes, south of mountain ranges in Europe and in Asia around Mediterranean sea and is characterized by warm temperate type climate.
Vegetation is chiefly composed of fruit trees, olives, nut trees, oranges, and also some foreign palms, cacti, acacias, etc. In the Asian region of Mediterranean as in Arab countries, rainfall is low, deserts are common and sparse vegetation includes species like Atriplex, Alhagi, and Polygonum and Phoenix dactylifera. (iii) Northern Africa. This zone includes the northern parts of Morocco, Algeria, Libya and Egypt. It is characterized by scanty rainfall and sparse vegetation. In cooler areas (i.e., mountains) some conifers and broad-leaved oaks are common.
In deserts (including some portion of Sahara desert) some herbs, shrubs, woody acacias and succulent xerophytes occur, (iv) Himalayas, eastern Asia and Japan Tibet, China and Japan have different type of vegetation. In China and Japan conifers like Cryptomeria, Sciadopitys, Cephalo- taxus, Ginkgo biloba and Cycas and angiosperms like Rhododendrons, Cinnamomum camphora and Begonia are common. The vegetation of Himalayas will be described later in this chapter.
(2) North temperate of the western hemisphere:
It includes the parts of United States and Canada lying mostly between north latitudes 30° to 55°. The eastern coastal regions of these countries in the temperate belt have some very characteristic plant species like tropical fern (Schizaea pusilia).
The forest communities are composed of conifers and deciduous trees. On lower altitudes some wild cherries, plums, roses and orchids are abundant. In the New England region trees of Ulmus Americana and Castania dentata are abundant. Forests of conifers are common in southern parts and on western parts of Rocky Mountains of USA. In north California grows Sequoia sempervirens, the tallest tree of world.
Ground vegetation is composed of Salicornia herbacea, Rumex maritima, Monotropa uniflora, Saxifragea, Primula, etc. In the Colorado Desert of Arizona and south-eastern California, there are several types of xerophytic plants.
This zone is divided into two sub- zones:
It comprises old world or eastern tropics and has the following two botanical regions: (1) Tropical Africa. This is a large-sized landmass of varied topography. It includes high altitudes and Sahara deserts which have little or no rainfall. In Africa, most remarkable plant is Welwitschia mirabilis; Eastern part of Central Africa has India-like vegetation of Borassus flabelliforntis, Tamarindus indica, Ficus, Aspargus, Clematis, and Phaseolus.
Cassia fistula, Erythrina, Acacia, Albizzia, Zizyphus, Bauhinia etc. (2) Tropical Asia. It includes Arabia, Pakistan, India, Burmai Ceylon, Thailand, Indonesia, Philippines and Islands of Indian Sea.
In Arabia, the rainfall is low and most of the desert species are found Coffea arabica is a native plant of Arabia. Ceylon is rich in species diversity and ferns are the chief components of its sparse natural vegetation, Malaya, Java and Sumatra are characterized by heavy rainfall and their vegetation comprises varied types of palms, some types of ferns, tall trees, lianas and insectivorous plants.
Some important plants of Java are Albizzia, Pterocarpus Tamarindus, Bombax, Cassia, Dendrocalamus, etc. The common trees of Burma and Thailand are jack fruit, orange, mango, banana, betelnut, etc.
It comprises Mexico and major part of South America. The low-rainfall areas of Mexico are rich in xerophytes. At higher cooler altitudes there is a forest of conifers like Pinus, Spruce, Quercus and Populus. On mountain peaks grasses are most common.
In wet areas of Mexico, there are mosses, palms, bamboos, orchids, etc. In South America, there are extensive forests of flood-resistant trees like Bertholletia excelsa, Maximiliana regia and also mangrove vegetation. There are also found many epiphytes.
South temperate zone:
This zone includes extreme southern region of Africa, Australia and New Zealand. In African area, the vegetation chiefly made up of ferns and gymnosperms. On the hills conifers are present. Is lower wet regions contain Salix and Phragmites and dry regions have grasses like Andropogon and trees like Acacia.
The vegetation of northern part of Australia is similar to that of south East Asia and includes trees of palms, nuts, Eucalyptus, Acacia and Casuartna. Some pteridophytes are also found in the ground vegetation. The South Australia Araucarias are common. New Zealand forests are mostly made up of conifers together with ferns, palm like Rhopalostylis, many species for Metrosideros. New Zealand has richest bryophytic flora.