The vegetation of Strandzha evolved before the formation of the Bosphorus Strait when the whole southern Black Sea coast was linked and represents the westernmost extension of the Euxine-Colchic ecoregion. Because of the proximity of three seas, the Black Sea, the Marmara Sea and the Aegean Sea, Strandzha remained unaffected by the Quaternary glaciation and retained its mild and relatively humid climate. Under those conditions the region has preserved relict species from the Neogene.