The rainfall, so unevenly distributed territorially, is, moreover, as unevenly distributed through the year. In most districts the principal rains are experienced in summer, the rainy season being followed by a long dry season. But on the Eastern coast the summer rains are slight, and the principal rainy season is delayed into October and November, while in Northern India and the Himalayas, also winter rains occur, irregular and of short duration. Even where a relatively large rainfall prevails, the climate is dry on account of the high temperature, hence some 30,000,000 acres of the cultivated acreage (which comprises 225,000,000 acres in all) depend on irrigation, over half of this irrigated area lying in the tropical zone. Roughly speaking, at least four climatic zones with many sub-types, may be recognized: the truly tropic, intensely hot and wet (over 75 inch rainfall), prevailing on the plains and tablelands of the lower half of the peninsula; the hot and dry (below 15 inch rainfall) climate of the Northwestern Indus plain and plateau; the moderately warm and dry to humid (30-75 inch rainfall) climate of the Ganges plain and central plateau; and the temperate to alpine, humid climate of the Himalaya mountains, with snow and ice in winter, and moderate heat in summer. In keeping with this great diversity of climate, both as to temperature and humidity, there is a great variation in the character and development of the forest cover. At least six types can be recognized, namely the evergreen forest, found along the West coast, in Burma, Andaman Islands, and the sub-Himalaya zone, which is composed of broadleaved species with a dense undergrowth of small trees and tangled lianas (vines), but few shrubs, as is characteristic of most tropical forest; the deciduous forest, mainly in the interior of Central India, with Sal, Teak and Ironwood as characteristic trees; the arid region forest, found in the Punjab, in Raiputana, and in Sindh, of varying composition, from the open shrub forests of the latter province, composed of acacias, tamarisk and mesquite, to the denser, more diversified, dry, low tree forest of the former; the alpine coniferous forest of the Himalayas and of the mountains of Afghanistan, Belutchistan, and Burma, composed of pine, deodar, juniper, with oak, walnut, boxwood, approaching our own forest types. In addition, there may be segregated the coast forest, of small extent, composed of trees which, like the mangrove, will bear salt water; the overflow forest along rivers; and river forests in the desert regions, of which latter large areas exist. The natural differences in the forest cover are emphasized by the action of man, who for many centuries has waged war against the forest, clearing it permanently or temporarily for agricultural purposes, or else merely burning it over to improve grazing facilities, or for purposes of the chase.