The Anatolian diagonal is a theoretical dividing line which runs diagonally across central and eastern Turkey from the northeastern corner of the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ...

to the southeastern corner of the

Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Rom ...

, and roughly cuts across part of the course of the upper Euphrates River within Turkey's borders.

Biogeographical barrier

The diagonal was first proposed by the British botanist

Peter Hadland Davis Peter Hadland Davis FLS, FRSE (18 June 1918 – 5 March 1992) was a British botanist. Life Davis was born on 18 June 1918 in Weston-super-Mare. Initially he was educated at the Nash House, Burnham-on-Sea and then continued his education at Br ...

in 1971. He noticed that many species of plant that existed west of the diagonal were not present to the east, while others found to the east were not present to the west. Of 550 species analysed, 135 were "eastern" and 228 "western". However, Davis considered that there were no

physical Physical may refer to: *Physical examination In a physical examination, medical examination, or clinical examination, a medical practitioner examines a patient for any possible medical signs or symptoms of a medical condition. It generally co ...

geological Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other E ...

climatic Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorological ...

differences or change in soil type that could account for the phenomenon. Not only does the Anatolian diagonal form a barrier to floral

biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...

, but about four hundred species of plant are

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

to this diagonal and are found nowhere else. Gypsum hills

In 1989, the Turkish botanists T. Ekim and A. Güner examined the distribution of species by detailed study of the ''Flora of Turkey'', eight volumes of which had been published by then. They came to the conclusion that the diagonal did indeed exist and they found that 33% of the plant species considered were affected by the diagonal in one way or another. They then considered the reasons behind the phenomenon. There was a difference in altitude between the two sides of the diagonal, with the land to the west being lower. Another difference was the climatological regions: to the west there were arid and semi-arid forms of the

Mediterranean climate A Mediterranean climate (also called a dry summer temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...

whereas to the east there were semi-arid, sub-humid and humid forms. In the middle portion of the diagonal there was a

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywal ...

feature, but what effect that had on plant distribution was unclear. They concluded that the ecological differences between the two sides of the diagonal were of greater significance than the palaeo-geological history of the area. The

Irano-Anatolian The Irano-Anatolian region is a biodiversity hotspot designated by Conservation International's Critical Ecosystem Partnership Fund, extending across portions of Armenia, Azerbaijan, Georgia, Iraq, Iran, Turkey, and Turkmenistan. This hotspot cov ...

region is a significant

biodiversity hotspot A biodiversity hotspot is a biogeographic region with significant levels of biodiversity that is threatened by human habitation. Norman Myers wrote about the concept in two articles in ''The Environmentalist'' in 1988 and 1990, after which the c ...

in the Near East and Anatolia is the transition point between the European and Turko-Iranian

flora Flora is all the plant life present in a particular region or time, generally the naturally occurring (indigenous (ecology), indigenous) native plant, native plants. Sometimes bacteria and fungi are also referred to as flora, as in the terms '' ...

s. Turkey was beyond the southern limit of ice in the last ice age, and Anatolia may be considered to be a potential

glacial refugium A glacial refugium (''plural refugia'') is a geographic region which made possible the survival of flora and fauna in times of ice ages and allowed for post-glacial re-colonization. Different types of glacial refugia can be distinguished, namely nun ...

for species of plants and animals in Europe. In the late Pleistocene, sea levels in this region were lower than they are today by as much as and

land bridge In biogeography, a land bridge is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonize new lands. A land bridge can be created by marine regression, in which sea leve ...

s intermittently formed across the Bosphorus and the

Sea of Marmara The Sea of Marmara,; grc, Προποντίς, Προποντίδα, Propontís, Propontída also known as the Marmara Sea, is an inland sea located entirely within the borders of Turkey. It connects the Black Sea to the Aegean Sea via t ...

. After the end of the most recent ice age, plants surviving to the west of the Anatolian diagonal could spread back into Europe while those to the east could spread into Syria, Iraq and the Near East. The

Taurus Mountains The Taurus Mountains ( Turkish: ''Toros Dağları'' or ''Toroslar'') are a mountain complex in southern Turkey, separating the Mediterranean coastal region from the central Anatolian Plateau. The system extends along a curve from Lake Eğird ...

provide a cool damp climate for species that cannot survive the hot dry summer climate on either side, and this could have encouraged survival and speciation, resulting in the many endemic species found here today.

References

{{reflist, 30em Geography of Turkey Natural history of Anatolia