Oceania: the general review.
In Pacific ocean, in its central and western parts there is the largest on globe a congestion of islands, a total area about 1,26 million the square kilometres which most part is grouped in archipelagoes. All islands unite under the name of Oceania.
Development of Ocaenia occurred in the conditions of long isolation from a continental land that defines a deep originality of its landscapes. It is shown both in a geological structure and a relief, and in high distribution of animal and vegetative organisms and poverty of specific structure of flora, fauna, especially on the most remote east islands.
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The specified reasons give the basis for allocation of Oceania in special parts of the world with domination of the oceanic landscapes, not having analogues on continents. The geological structure of islands of Oceania is in a direct communication with a structure of a bottom of Pacific ocean. Almost all islands of a coral or volcanic origin.
In the central part of Oceania (in Polynesia and east Micronesia) they represent tops of underwater volcanoes. Underwater ridges, erected powerful outpourings of basalt lavas in the end of a neogene and in quaternary the period on lines of breaks of an ancient oceanic platform of a bottom of Pacific ocean. Formation of coral islands occurred in quaternary the period in connection with ecstatic fluctuations of level of Pacific ocean and deflections of parts of its bottom.
The islands concentrated to a West side of Oceania, lay in geosynclinal belt the structures framing the central platform, and are tops of grandiose underwater ridges-front lines of constructions geosynclinal belt.
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From the external (oceanic) party these islands are framed with deep-water hollows. orogenicmovements in peripheral Pacific geosynclinal belt were actively shown in mesozoic and Alpine cycles, but have not ended and now to what frequent both strong earthquakes and active volcanism on islands testify.
Islands of the western Oceania the largest and mountainous.Among them New Zealand and New Guinea are allocated with the sizes and a high-mountainous relief, on which share 80 % of the area of a land of Oceania are necessary.
Islands are scattered in latitudes from subtropical in northern hemisphere to temperated in southern, but their big part is concentrated in subequatorial zones that defines the basic features of a course of temperatures.
Land influence affects on a climate of the closest to Australia and South East Asia islands.
For the others small daily and seasonal amplitudes of heats are characteristic. Constantly high humidity of air and a considerable quantity of precipitations. Average temperatures of the warmest months (August in northern hemisphere, February in southern) change from 25°С in the north to 16°С in the south, the coldest (February and August) from 16°С to 5°С. Sharp changes of seasonal and daily temperatures are characteristic only for mountainous islands. On New Zealand and New Guinea high-rise climatic zones come to an end with a nival climate.
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On windward mountainside evergreen damp woods grow.
On leeward mountainside the mixed woods, original oceanic savannas with rigid cereals, pandanuses, groves of coconut palm trees are prevail.
Large islands of Oceania were the centres of formation of flora. At the same time many kinds of plants migrated on islands from Australia, and mainly, from Malay archipelago and South East Asia.
The question on distribution of organisms in Oceania remains not resolved. Usually believe, that migration occurred on temporary bridges of a land. On the other hand, it is impossible to underestimate a role of winds, currents, birds and, at last, people, in an extreme antiquity making long swimmings between archipelagoes.
The greatest prevalence of flora New Zealand and the Hawaiian Islands possess. Among plants of Oceania a lot of useful to the person coconut and sago-palm trees, bananas, a mango, melon and grain trees.
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