Approximately 17 million years ago, most parts of Iran were covered with humid forests and there was plenty of fresh water everywhere. However, the weather gradually became drier around 10 million years ago, transforming the landscape to a savanna and isolating forests to smaller areas.
6-7 million years ago, the north-west of Iran was home to many prehistoric mammals like Smilodonts, Hiparions and Mastodonts (the ancestors of lions, horses and elephants). Now, it holds the remains of these prehistoric mammals, with most of them located in the famous fossil zone of Maragheh in the foot of Sahand volcanic mountain.
During last million years Iran has been affected by severe climatic conditions of which ten glacial periods are the most important ones. Most of today’s deserts and high mountains came into existence produced in this period. This facilitated the process of speciation in many taxa. Many populations retreated from higher latitudes to south and opposite and also from high altitudes to lowlands and opposite.
Considering this geological history we can divide the country into 8 natural zones:
1. North-west Zone
This zone consists of Azerbaijan and adjacent territories. This area is partially volcanic with scattered high mountains. This region possesses very cold winters with heavy snow, and mild summers. The highest point is Mount Sabalan (4811 m). Many parts of this zone are filled with xerophytic and steppe mountains at low or middle altitudes.
However, there are many green meadows at higher altitudes. Some important forest patches occur in the west of West Azerbaijan at the border of Turkey and in the north of East Azerbaijan in Arasbaran Mountains. This is a part of the Caucasus Ecoregion, and the Arasbaran forests, which is a very important natural reserve, is named small Caucasus of Iran. The Region is home to many important animals (e.g. Lynx, Wild Cat, Badger, Marbled Polecat, Brown Bear, Wolf, Leopard, Red Deer, Roe Deer).
2. Alborz Mountain Zone
This zone has cold winters with moderate summers. It is much drier in southern slopes and humid in northern slopes. Spring arrives in May and the first snow appears in late August. From hill side to middle altitudes the flora is xerophytic, but from 2500m to 3500m it changes to subalpine, and in higher altitudes it turns to alpine meadows.
In northern slopes it is particularly humid with regular dense mist which has given way to very green meadows with many different butterfly species. Permanent snow can be seen from 3600m upwards. The most significant animals for this zone are: wild goat and sheep, wild boar, lynx, leopard, brown bear, stone marten, least weasel, Purcupine, fox, wolf, red deer, otter, etc. Many endemic species exist in this zone. In reptiles: Montivipera ebneri, M. latifii, M.albicornata, Lacerta defillippi, etc.
3. Hyrcanian Forest Zone
This zone is very humid, with plenty of rainfall and misty days throughout the year. This is one of the oldest forests of the northern hemisphere and a relic from the last glacial periods. The most significant animals in this region are: the Siberian Crane, different species of ducks and wetlands birds, red deer, roe deer, jungle cat, corsac fox, European pine marten, badger, Caspian seal and extinct Hyrcanian Tiger.
4. North-eastern and Eastern Zones
This zone covers the areas in the north-east including Kopet Dag and Aladag Mountains with the highest point being the Binaloud peak(3200m). This zone offers dry and cold winter and relatively warm summers, with much rain in late winter and spring.
A large part of this zone is a desert or semidesert land with scattered mountains reminiscent of Central Asian habitats. The fauna and flora of this area are deeply affected by Central Asian ones. Some significant animals in this zone are: Leopard, wild sheep (Urial), Jebeer Gazelle, goitered gazelle, Persian wild ass, striped hyaena, Pallas’s cat, sand cat, wild boar, etc.
5. Central Mountains and Kerman Zones
This zone covers a mountain chain from Tafresh in the north west to Kerman mountains in the south east. There are many high peaks of which the most important ones are Karkas (3895 m), Shirkuh (4055 m), Lalezar (4351 m), Hezar (4501 m) and Jopar (4135 m). This zone offers cold and dry winters, and less rain or snowfall in higher altitudes in late autumn and winter.
There is permanent snow at altitudes higher than 3800m. This zone is affected by both Central Asia and Mediterranean fauna and flora. There are many endemics found in this zone as it has been isolated from other zones with wide deserts from both east and west. The lowlands steppe flora includes Atraphaxis, Zygophyllum, Haloxylon, Astragalus, Artemesia, Acantholimon and Acanthophylum species. In higher areas there are mostly Astragalus and rarely
Onobrychis cornuta with scattered trees like Pistacia and Amygdalus bushes. There are not so many green meadows except for small areas and that may be found only in early spring. The animals inhabiting this zone are: cheetah, stripped hyaena, caracal, sand cat, sand fox, wild ass, goitered gazella, hubara bustard, etc.
6. South-eastern Zone
This zone covers the mountains of south east and shore lines of the Sea of Oman. This zone holds hot summers with mild winters and wet weather in late winter. The highest points are Taftan volcanic mountain (4042m) and Bazman Volcano (3503m). But most parts are dry lowland which turns to savanna in the south.
The climate of this area is affected by monsoon arriving from South Pakistan and India. The fauna and flora are also very close to those, and therefore this area is called the Iran’s little India. Vegetation includes Acacia, Prosopis, Cadaba, Zygophyllum, palm, citrus, Banana and the most significant animals are: Asian black bear, Baluchi squirrel, smooth-coated otter, honey badger, small Indian mongoose, fruit bat, Gando (mugger crocodile) etc.
7. Zagros Zone
This zone covers a vast area stretching from the northwest to the southeast with cold winters and warm summers in lowlands but mild at higher altitudes. This region offers heavy snow fall in high mountains that remain until next winter. This is one of the most important areas for speciation and evolution of many species including butterflies.
The characteristic shape of the mountain with deep and steep valleys that absorb the humidity coming from west has created vast oak forests. Each peak in Zagros can act as an isolated island with its own climatic character. Some significant animals for this zone are: brown bear, wild boar, wild goat and sheep, Lorestani Salamander (Neurorgus kaiseri) endemic to Zagros, and two more species of Salamanders, Reptiles: Iranolacerta zagrosica, L. yasujica and Vipera urarachnoides. Vegetation in the western region is generally oak forests, which in some parts of central and northern Zagros is more humid; but in the western region the normal scene is xerophytic steppes with Astragalus, Acantholimon, Artemisia and Onobrychis cornuta bushes. In high altitudes there exist mainly different kinds of cushion like species: Astragalus, Acantholimon and Onobrychis cornuta together with many other endemic plants like Dionysia, Salvia, etc.
8. South Coastal and Islands Zone
This region includes the foothills of Zagros Mountains in the north of the Persian Gulf. In the north-western part, it is much wider and forms a flat plateau in Khuzestan province. In southern parts, it is narrower with some rocky hills near the sea. In some areas there are also sandy hills like what we see in central Iran.
This zone possesses hot and damp summers and mild winters with main precipitation in winter and early spring. The main plants are Halophyte species like Salsola, Prosopis, Acacia, Zizyphus, palm and citrus trees. Some significant animals for this zone are: Striped hyaena, Indian mongoose, golden jakal, Persian fallow deer, goitered gazelle and extinct Persian lion.