Читать книгу North American Agroforestry - Группа авторов - Страница 77

In large areas in the Great Plains, particularly in the more xeric short‐ and mixed‐grass prairies, grasses and forbs exist largely independently of any woody species. The same situation exists in some of the larger high‐elevation meadows in the Rockies and, pre‐settlement, the grasslands of the Central Valley of California and the Palouse Prairie of eastern Washington.

How small a grassland can be before adjacent woodlands have a significant effect is, of course, a key question in terms of agroforestry design. Long‐term—i.e., hundreds or thousands of years—these grasslands did not remain isolated, as evidenced for example by the presence of conifers throughout the Great Plains during the various glacial periods (Axelrod, 1985).