Pine barrens, pine plains, sand plains, or pinelands occur throughout the northeastern U.S. from New Jersey to Maine (see Atlantic coastal pine barrens) as well as the Midwest, Canada and northern Eurasia. Pine barrens are plant communities that occur on dry, acidic, infertile soils, dominated by grasses, forbs, low shrubs, and small to medium-sized pines. The most extensive barrens occur in large areas of sandy glacial deposits (including outwash plains), lakebeds, and outwash terraces along rivers.
The most common trees are the Jack pine, red pine, pitch pine, blackjack oak, and scrub oak; a scattering of larger oaks is not unusual. The understory includes grasses, sedges, and forbs, many of them common in dry prairies, and rare plants such as the Sand-plain Gerardia (Agalinis acuta). Plants of the heath family, such as blueberries and bearberry, and shrubs, such as prairie willow and hazel, are common. These species have adaptations that permit them to survive or regenerate well after fire.
Barrens are dependent on fire to prevent invasion by less fire-tolerant species. In the absence of fire, barrens will proceed through successional stages from pine forest to a larger climax forest, such as oak-hickory forest.
European settlers found extensive areas of open game habitat throughout the East, commonly called "barrens". The American Indians used fire to maintain such areas as rangeland. Open barrens are now rare and imperiled globally. Suppression of wildfires has allowed larger climax forest vegetation to take over in most one-time barrens. In North America, barrens exist primarily in the American Midwest and along the East Coast.
In 1968, John McPhee published a book, titled The Pine Barrens, exploring the history, ecology and geography of the New Jersey Pine Barrens. His account is also infused with his personal memoirs. His book contributed to a reappraisal of the ecological role of pine barrens; in New Jersey and on eastern Long Island, they contribute to preserving the amount and quality of vital groundwater supplies in underground aquifers.