A Holocene climatic optimum in the Eastern Woodlands, equivalent to the Altithermal segment of the Holocene Epoch (Holocene is 10,000 years ago-present), dated on the basis of pollen studies. The Hypsithermal Climatic Interval began about 9,000 years ago and ended about 2,500 years ago. It has been divided into smaller units beginning with the Boreal. The Hypsithermal follows the Pre-Boreal and precedes the Sub-Atlantic intervals. It was a time of comparatively warm climatic conditions which resulted in the elimination of many cooler plant and animal refuges and the extinction of some species. In many parts of the world, pine forests gave way to forests dominated by oak during the Hypsithermal. Mesolithic and Neolithic cultures are contemporaneous with Hypsithermal events in both the New and Old Worlds.