More than one-tenth of the country is forested. The most extensive growths are found on the mountain slopes rising from the Caspian Sea, with stands of oak, ash, elm, cypress, and other valuable trees. On the plateau proper, areas of scrub oak appear on the best-watered mountain slopes, and villagers cultivate orchards and grow the plane tree, poplar, willow, walnut, beech, maple, and mulberry.
Having two important mountain ranges of Alborz and Zagrus cause to be introduced as one of the world's most mountainous countries that attracts many tourists and mountain climbers every year.
Iran's land surface covers 165 million hectares, more than half of which is uncultivable. A total of 11.5 million hectares is under cultivation at any time, of which 3.5 million hectares were irrigated in 1987, and the rest watered by rain. Only 10 percent of the country receives adequate rainfall for agriculture; most of this area is in western Iran. The water shortage is intensified by seasonal rainfalls. The rainy season occurs between October and March, leaving the land parched for the remainder of the year. Immense seasonal variations in flow characterize Iran's rivers.
Iran consists of rugged, mountainous rims surrounding high interior basins. The main mountain chain is the Zagros Mountains, a series of parallel ridges interspersed with plains that bisect the country from northwest to southeast. Many peaks in the Zagros exceed 3,000 meters above sea level, and in the south-central region of the country there are at least five peaks that are over 4,000 meters. As the Zagros continue into southeastern Iran, the average elevation of the peaks declines dramatically to under 1,500 meters.
Most of Iran is considered as the center of origin of many genetic resources of the world, including many of the original strains of commercially valuable plant species such as wheat, or medicinal and aromatic species. The southwest has some Afro-tropical features, while the southeast has some species from the Indo-Malayan sub-tropical realm.
The wetlands of Iran are globally significant. Large populations of migratory birds winter at these wetlands or use them on their way to and from wintering areas in Africa or the Indian Sub-continent. The marshes of the south Caspian lowlands in Iran's northwest are particularly important for over 20 species of ducks and geese while the mud flats of the Persian Gulf coast are of critical importance for shore birds, gulls and terns. A variety of marine mammals is observed in the southern waters of Iran.